NO761414L - - Google Patents

Description

"Sensor for devices for drilling boreholes".

The present invention relates to devices which serve for drilling boreholes, and which include sensing and telemetry means for periodically sensing directional parameters for a drill string in the borehole and for generating output signals which are transmitted to the surface.

In the field of well drilling, especially oil and gas well drilling, the utility of a system capable of detecting certain parameters at the bottom of a drill string and of transmitting such data to the surface during the drilling operation has long been recognized.

While some proposals and systems for borehole telemetry have included arrangements where sensor packages are periodically lowered into and raised from a wellbore, the vast majority of preferred arrangements will have their parameter sensing devices permanently located at the bottom of the well, preferably in a lower segment of the drill string, and transfer data to the surface. A number of systems have been proposed for carrying out such sensing and data transmission. One of the main types of such systems is the mud-pulse telemetry system where pulses are generated in the mud column in the drill string to transmit data to the surface.

The permanent lower hole position of the parameter sensors

however, makes the factors of reliability, accuracy and repeatability of the parameter determination all the more important. Otherwise, the driller will have no really accurate indication of the direction of the wellbore unless the parameter sensors are very accurate, or serious loss of time and costs can occur if it becomes necessary to remove the drill string out of turn.

One purpose of the present invention is to provide

new and improved sensing means for a device for drilling of

borehole and organs to control its operation, with which the aforementioned disadvantages are eliminated or significantly reduced and very accurate, reliable and repeatable measurements of directional parameters in a borehole are obtained.

According to the present invention, a sensor has been provided for periodically sensing directional parameters for a drill string in a borehole and for producing output signals which are in accordance with the measured parameters, and which are to be transmitted to the surface, and the characteristic of the sensor according to the invention is that the sensing means comprises a three-axis pendulum with means that respond to gravity and serve to determine a vertical plane and a horizontal plane, and with other means that respond to magnetism and serve to determine the setting relative to the direction of the Earth's magnetic field, a motor- drive means for moving the first and second members from first predetermined positions to second predetermined positions, each having a predetermined setting with respect to the direction of gravity and the earth's magnetic field, and a control means for controlling the operation of the motor-drive means and for measuring the total displacement of each of the first and a change bodies between the first and second positions.

According to a preferred embodiment, the first means responsive to gravity include error conversion accelerometers each having an axis sensitive to the direction of gravity, while the second means responsive to magnetism include a magnetometer with an axis sensitive to direction of the earth's magnetic field.

An outer wobble hoop, known as the reference wobble hoop, measures the reference angle between a reference mark on the drill string and the vertical plane containing the drill axis. An intermediate wobble bar, or the inclination wobble bar, measures the angle of inclination of the drill axis in relation to the vertical. An internal or magnetometer oscillating bar measures the angle between the horizontal projection of the bore axis and magnetic north in the horizontal plane. The sensor package is designed to be contained in the drill string, and the construction is thus comparable to a cylindrical shape where the diameter is limited by the diameter of the drill string, but where there is no significant limitation in terms of length.

The reference slinger consists of a tubular structure which can freely rotate coaxially with the drill string inside a stationary pipe in it. An accelerometer is arranged on the reference wobbler with its sensitive axis perpendicular to the axis of rotation of the reference wobbler. The reference angle is measured by determining the movement necessary to move the accelerometer from a "home position" to a position where the output signal from the accelerometer is zero. The reference angle is preferably measured by counting the number of steps that a stepping motor must cover from a known home position to a position where the output signal from the reference accelerometer is zero.

The inclination-sling bracket for measuring the inclination angle is arranged, inside the reference-sling bracket. The inclination swing bracket also has an accelerometer with which the angle of inclination is measured by determining the movement required to bring the accelerometer from a home position to a position where the output signal from the accelerometer is zero. The angle of inclination is preferably measured by counting the number of steps that a stepper motor must travel to move the inclination-wobbling bracket from a known home position to a position where the output signal from the accelerometer is zero.

Another wobble bar inside the reference wobble bar is arranged parallel to the inclination wobble bar and slave-connected to this. This third wobble bar, which carries the magnetometer, is carried by this further slaved wobble bar. The azimuth angle is also measured by determining the movement required to bring the magnetometer from a home position to a position where the output signal from the magnetometer. is zero. The azimuth angle is preferably measured by counting that number

steps that a stepping motor must perform to bring the magnetometer to a known zero position relative to the Earth's magnetic field.

Upon receipt of an initiation signal that is compliant

with a state of no rotation of the drill string, the operation of the control device, which had previously been inactive, is started. The controller first operates in a "home" mode where the output signal from a pulse generator is transmitted to each stepper motor to drive the wobblers and error transducers to a predetermined home position. When signals appear indicating that the home position has been reached for all fault inverters, the "home"-

mode and a "measure" mode of operation is initiated.

In "measure" mode, error signals from each error converter are examined (in accordance with the deviation from a desired zero position)

in sign and magnitude detecting circuits to determine the magnitude of the error and the direction of movement of the transducer needed to reduce the error, and the pulse generator is actuated to produce step pulses for the step motors. The net number and direction of the steps the stepper motor must perform to bring a converter to its zero position are counted and stored in a counter and constitute a measure of the angular information sought from the device. The operation of each pulse generator is terminated to stop the motor when the inverter zero position is reached. When the operation of the pulse generators and stepper motors connected to all the error converters has ended, a "done" signal is produced, whereby the information in the counter is entered into a shift register and finally transferred to the surface.

Operation in the sequence "home" mode-"measure" mode repeats until a signal is received consistent with a regained rotation state, after which operation of the control device is terminated.

In the case of several classes of data, it is completely unnecessary to take readings more often than once. every ten meters or so of the well depth. This corresponds to readings from every fifteen minutes to every hour and a half at typical drilling speeds of

about. 4 0 - 6.5 m/h. It is therefore desirable to switch off the downhole parameter sensing equipment during long periods of drilling to greatly reduce the wear and tear that would otherwise have resulted from continuous operation of the parameter sensors.

In order to determine the state of no rotation of the drill string, according to the present invention, a rotation sensor is arranged to sense the absence or presence of the rotation of a rotatable part in a surrounding magnetic field to activate a control mechanism in the absence of rotation of the part. The rotary sensor comprises a fluxgate magnetometer which serves to produce an output signal as a function of the angular position of the magnetometer with respect to the direction of the surrounding magnetic field and adapted to be placed in a drill string segment, means for producing and transmitting an input signal to the fluxgate magnetometer, having a first output signal which is a harmonic of the input signal, a first detector for receiving the first output signal, means for producing a reference signal having the frequency of the first output signal and applied to the first detector, which compares the phase difference between the first output signal and the reference signal and produces a second output signal whose frequency is in accordance with the rotational speed of the drill string, second detector means for receiving the second output signal and for generating a third output signal each time the second output signal crosses a reference level, and signal generating means for receiving the third output signal and for producing a fourth output signal when the third output signal corresponds to absence of rotation.

The present invention will be better understood and its numerous purposes and advantages will become clearer to those skilled in the art in light of the drawing, which illustrates the invention by way of examples.

Fig. 1 is a schematic overview drawing of a borehole

and a derrick and visualizes the application environment of the invention.

Fig. 2 is a view, partly in axial section, of a section of the drill string in fig. 1, and shows the parts of the drill string that accommodate the object of the invention. Fig. 3 is a perspective view, partly in section, of a detail in fig. 2. Fig. 4 is a perspective view of the flux magnetometer in the rotation sensor.

Fig. 5 is a block diagram of the rotation sensor.

Fig. 5A is a diagram of the digital filter of fig. 10B. Figs. 6A, 6B and 6C show curves for output signals in different positions of the rotation sensor in Fig. 5. Fig. 7 is an isometric view of the sensor for determining inclination, reference and azimuth angles. Fig. 8 is a representative curve for the output signal from one of the accelerometers in fig. 7. Fig. 9 is a representative curve for the output signal from the magnetometer in fig. 7. Fig. 10A and 10B constitute a block diagram of the control device. Figs. 11A, 11B and 11C are a connection core for the control device of fig. 10A and 10B. Fig. 12 is a diagram of the initiation control in fig. 10B.

Fig. 13 is a diagram of the main clock in fig. 10B.

Fig. 13A shows the output pulses from the main clock and frequency divider circuit. Fig. 14A shows a signal which the summing unit in fig. 10A supplies the sign and magnitude detector. Figs. 14B, 14C, 14D and 14E show output signals from the sign detector of FIG. 10A.

In fig. 1 shows the general environment in which the present invention is used. However, it should be understood that the general depiction in fig. 1 should only serve to show representative environments where the present invention can be used, and it is not intended to limit the application of the present invention to the particular structure in fig. 1.

The drilling apparatus in fig. 1 has a derrick 10 carrying a drill string or drill stem 12 which terminates in a drill bit 14. As is well known in the art, the string may rotate, or the drill string may be held stationary and only the drill bit rotated. The drill string 12 is composed of a number of interconnected segments, new segments being added as the depth of the well increases. The drill string hangs down from a movable block 16 suspended in a winch 18, and the entire drill string is brought into rotation by means of a square holder 20 which is guided slidingly through, but is taken into rotation by a turntable 22 at the foot of the derrick. A motor device 24 is connected to both drive the winch 18 and to turn the turntable

22. The lower part of the drill string may contain one or more segments 26 with a larger diameter than other segments of the drill string. As is well known in the art, these thicker segments may contain sensors, electronic circuits therefor and power sources, e.g. mud-driven turbines that drive generators to supply electrical energy to the sensing elements. A typical example of a system where a mud turbine, a generator and sensor elements are contained in a lower segment 26 is shown in US-PS 3,693,428.

Drilling material produced during the operation of the drill bit 14 is carried

away by means of a powerful mud flow that rises up through the free annular space 28 between the drill string and the wall 30 of the well. The mud is delivered via a pipe 32 to a filtration and decanting system, schematically shown as a tank 34. The filtered mud is then sucked away using a pump 36 equipped with a pulsation absorber 38, and delivered under pressure via the line 40 to a rotatable injection head 42 and from there to the interior of the drill string 12 to supply the drill bit 14 and the mud turbine if a mud turbine is included in the system.

The mud column in the drill string 12 also serves as a transmission medium to conduct signals regarding drilling parameters that occur along the well to the surface. This signal transmission is carried out by means of the well-known technique of mud pulse generation where pressure pulses representing the sensed parameters along the well are produced in the mud column in the drill string 12. The drilling parameters are sensed in a sensor unit 44 (see also fig. 2) in a drill collar unit 26 close to or adjacent to the drill bit. There, pressure pulses are created in the mud flow in the drill string 12, and these pressure pulses are received by a pressure transducer 4 6 and transferred from there to a signal receiver unit 48 which can record, display and/or perform calculations on the basis of the signals to provide information about different conditions down the well.

Whereas brief reference should be made to fig. 2, this schematically shows a system in a drill string element 26 where the mud pulses are generated. The mud flows through a variable orifice 50 and is discharged to drive a turbine 52. The turbine provides power to a generator 54 which supplies electrical energy to the sensors in the sensor unit 44. The output signal from the sensor unit - in the form of electrical or hydraulic or similar signals - drives piston 56 which changes the size of a variable opening 50, the piston having a valve driver 57 which can be maneuvered hydraulically or electrically. Variations in the size of the opening 50 create pressure pulses in the mud flow, which transmit these to the surface, where they are sensed to give indications of different conditions sensed by the sensor unit 44. Mud flow is shown by the arrows.

For many classes of data or parameters to be sensed at the bottom of the well, it is completely unnecessary to sense data and take readings more often than once every ten meters of depth or thereabouts. This corresponds to readings from every fifteen minutes to every hour and a half at typical drilling speeds of approx.

40 - 6.5 m/h. It is therefore desirable to switch off the entire sensor equipment during long periods of drilling in order to reduce as much as possible the wear and tear on sensors, transmitters and other parts of the telemetry system that would otherwise have resulted from continuous operation. The invention as illustrated in Figs. 3-6, is aimed at this move, which involves turning off the parameter sensor equipment when sensing and distinguishing between periods of rotation and absence of rotation of the drill string. The invention requires a rotation sensor to detect rotation of the drill string and interrupt the delivery of electrical energy to the well parameter sensors when the drill string is rotated, and conversely to allow the delivery of energy to the well parameter sensors when the drill string is not rotated. A magnetic detection means which senses the earth's magnetic flux is used as a rotation sensor to detect the presence or absence of rotation of the drill string. This rotary sensor contains no moving parts and therefore, unlike other motion sensors, which may contain moving elements, provides high reliability regardless of whether it is exposed to mechanical shocks and vibrations.

In fig. 2 and 3 show some details of the drill string segment 26 which houses the rotation sensor 58 according to the present invention. As both the rotation sensor and one or more other sensors in the sensor unit 4.4 are magnetically sensitive, the special drill string segment 26A which accommodates the rotation sensor according to the invention and the other sensor elements, be a non-magnetic section of the drill string, preferably made of stainless steel or mo.nell. The rotation sensor 58

can be included in the sensor unit 44 or be made as a separate package, and for the sake of simplicity it is shown as part of the sensor unit 44 in fig. 3. The sensor unit 44 is further built into a non-magnetic pressure vessel 60 which serves to protect and insulate the sensor unit against pressure occurring down in the well.

In fig. 4, the rotation sensor 58 is shown as a toroidal flux gate magnetometer which is used to determine the direction of the earth's magnetic field. Although many other types of flux detectors can theoretically be used, the ring core flux gate magnetometer is used because of its low energy consumption and its solid physical structure. The operation of the toroidal fluxgate magnetometer is based on the non-linear or asymmetric characteristics of the magnetically saturable transformers used in the sensing element.

As seen in fig. 4, the device has an annular core 62 suitably wound (winding details not shown), an input or primary winding 64 and an output, secondary or sense winding 66. The core 62 is made of a material having a square B-H housing - Terese curve, e.g. permalloy. The characteristic of this device is such that the output signal from the secondary windings, i.e. the voltage induced in the secondary windings when the core is saturated by suitable alternating current energization of the primary winding in the absence of an external magnetic field, will be symmetrical, i.e. containing only various harmonics of the fundamental oscillation of the driving current . In the presence of an external magnetic field, e.g. the earth's magnetic field, the output voltage from the secondary winding will, however, become asymmetric, since second-order and other equal harmonics of the primary frequency appear on the output from the secondary winding. This asymmetry is in size and direction in relation to the signal field and can be detected by several known techniques. Reviews of such fluxgate magnetometers can be found in an article by Gordon and Brown, IEEE Transactions on Magnetics, Volume Mag-8, No. 1, March 1972, an article by Geyger, Electronics, June 1, 1962, and an article by R. Munoz, AA-3.3,

1966, National Telemetering Conference Proceedings, all of which provide a more detailed description of the structure and theory of operation of the magnetometer.

For the application of the present invention, the input signal to the primary winding 64 will saturate the core 62 twice for each period of the primary winding input signal. The time when the core becomes saturated is related to the surrounding external magnetic field which is superimposed on the drive field in the core. That is that saturation of the core varies as a function of the strength and direction of the earth's magnetic field, which is shown schematically by the flux lines in fig. 4.

The sensor 58 is physically placed on a shaft 68 which is held in a drill string segment 26A and lies in or parallel to its axis of rotation. When the drill string is rotated, the rotation sensor 58 is also rotated in the surrounding earth magnetic field. When the rotary sensor 58 is rotated, the combined effect of the input signal to the primary winding 64 and the surrounding earth magnetic field will result in a varying phase shift of the second harmonic output signal on the secondary winding 66.

In fig. 5 shows a block diagram for processing the output signal from the rotation sensor. The input signal to the primary winding 64 comes from an oscillator 61, its oscillation frequency being halved by the frequency divider 63, and the resulting signal is transferred to the amplifier 65 and then to the primary winding 64. The output signal from the secondary winding 66, which by means of a capacitor 67 is tuned to the second harmonic of the input signal to the primary winding, is transmitted to a buffer amplifier 69 and then to a phase sensor 70A in a detector 70. The detector 70 also includes a low-pass filter 70B and an amplifier 70A. The output signal from the oscillator 61 (with the same frequency as the second harmonic output signal from the secondary winding) is likewise transmitted to the phase sensor.70A. The phase angle of the second harmonic output signal from the secondary winding 66 is a function of the rotational speed of the magnetometer 58 and thus varies as a function of the changes in the magnetometer's rotational speed. The output signal from the secondary winding 66 is compared with the output signal from the oscillator 61 in the phase sensor 70A, where the phase difference between the two signals is sensed and transferred to the low-pass filter 70B. The output signal from the filter 70B (when the drill string rotates) is an alternating voltage signal which varies in frequency as a function of the degree of change of the phase angle of the second harmonic output signal from the secondary winding 66, i.e. the output signal from the filter 70B varies in frequency as a function of the changes in the rotational speed of the drill string . The output signal from the filter 70B is amplified in the amplifier 70C and then transmitted to a zero crossing detector 72 which emits an output pulse each time the alternating current signal from the detector 70 passes zero. The pulses produced by the zero crossing detector 72 (which is also a

function of the rotation speed of the drill string), is transmitted to a digital filter 74 which provides output signals corresponding to the states of rotation or no rotation.

As shown in fig. 5A, the filter 74 includes a frequency-dividing counter 75, an S-R type flip-flop 76, J-K type flip-flops 77 and 78 and an AND gate 79 connected as shown. The output pulses from the zero crossing detector 72 are transmitted to the input C of the divider counter 75. Assuming that the drill string normally rotates, - the pulses transmitted to the counter 75 cause it to exceed its maximum value before it is reset by a clock pulse CPN (which can be an arbitrarily chosen whole measure of a clock pulse commensurable with a predetermined minimum rotation speed), whereby the Q output of the counter 75 assumes a high level. The Q output signal from counter 75 is connected to the S input

to the flip-flop 76 so that the high level of the Q output signal from

the counter 75 sets the flip-flop 76, whereby the Q output signal from the flip-flop 76 assumes a high level and the Q output signal assumes a low level. The Q output of flip-flop 76 is connected to the J input of • flip-flop 77. Flip-flop 77 is initially set to the output position by a reset pulse CLEAR which can be diverted from any convenient location when power to the control device is turned on. The J input signal to the flip-flop 77 is examined at the leading edge of each pulse CPN which is transferred to the C input of the flip-flop 77, whereby the J input signal is transferred to the Q output. When the drill string is normally rotating, the counter 75 will continuously exceed its maximum value and is then reset by the clock pulses CPN, the flip-flop 76 is continuously set by the Q output signal from the counter 76 and reset by the upper level of the clock pulses CPN, and the J input signal to flip-flop 77 is at a low level whenever it is probed at the leading edge of the CPN pulse at the C input of flip-flop 77. Thus, the Q output from flip-flop 77 is also at a low level when the drill string is normally rotating, and a first output level indicating rotation, is transmitted from filter 74 (see level X, Fig. 6C).

In fig. 6, the various signals discussed above are shown schematically. The abscissa represents for each curve the time, and the ordinate for each curve represents the signal amplitude. Fig. 6A shows the second harmonic<*> output signal from the detector 70, Fig. 6B shows the pulse output from the zero crossing detector 72, and FIG. 6C shows the output signals from the digital filter 74. From time T. to T_ in all the curves, the drill string rotates at a constant speed. As the drill string decelerates and approaches the no-turn condition (after time T^), the frequency of the output AC voltage signal from detector 70 decreases and thus leads to a lower frequency output signal from zero-crossing detector 72.

When the drill string stops turning or the rpm drops to a very low level on the way to a no-turn state, the pulses will stop. the zero crossing detector 72 drops below a predetermined minimum frequency corresponding to a predetermined low rotational speed of the drill string. Since the angular velocity of the drill string must pass decreasing levels on the way from normal to zero rotation, a predetermined low rotation rate can

(of the order of 3 rpm or less) be used as a sig-

nal for no rotation, as the rotation is about to cease and will have ceased within the time required to initiate operation of desired sensors that operate when the rotation has ceased.

When the rotation ceases or drops below the predetermined low speed, which signals the imminent condition of no rotation, the counter 75 will not exceed its maximum value until it is reset by the clock pulse CPN. The Q output signal from the counter 75 thus remains at a

low level and the flip-flop 76 will not be set. Because the rocker 76

is not set, the Q output signal from the flip-flop 76 will be at a high level, and likewise the J input signal to the flip-flop 77. The leading edge of the clock pulse CPN then sets the flip-flop 77, whereby the Q output signal from the flip-flop 77 will be at a high level (see level Y in Fig. 6), indicating the condition of no rotation. When the output signal from the zero-crossing detector 72 with the predetermined minimum frequency is thus maintained for a given time period from T2 to T3 (eg 10 s), the digital filter output signal (ie the Q level of the flip-flop 77) as shown in fig. 6C, be shifted to another level, indicating a state of no rotation (see level Y in Fig. 6C). This second output level, corresponding to a state of no rotation, is then used as a control signal for activation or energy supply of the other sensor elements in the sensor unit 44. - Before the generation of this control signal, the other sensor elements in the unit 44 have no energy supply. The control signal (ie the second output level from the digital filter 74) is used as a signal to arm or transfer the energy from the generator 54 to the valve driver 57 and to the other sensor elements, e.g. by the action of flip-flops or arming gates to enable energy to be delivered to other sensing elements in the sensing unit 44, or in any other desired manner for this purpose.

Fig. 7 shows how the sensor elements in the sensor unit 44

is arranged and operated according to the invention. This concerns the sensor units for sensing various parameters that occur along the well, and which are to be sensed after rotation has ceased, and periodically transferred to the surface to provide a measure and an indication of certain directional parameters at the bottom of the well.

The parameters to be measured and determined according to the invention are directional parameters for the drill pipe, in particular a drill pipe that runs at an angle either from the original starting point or from an intermediate point in the well. As is known from the existing art (see, for example, US-PS 3,657,637), the parameters for inclination angle, azimuth angle and reference angle must be known in order to have complete information about the position and direction of the drill string. For the sake of overview, the following definitions of the different angles are presented: 1. Inclination angle (I) is the angle of inclination for the drilling axis in relation to a vertical line (V) in the vertical plane of the drilling axis. In fig. 7, the bore axis is denoted by X<1>X and

I = XOV.

2. Azimuth (A) is magnetic azimuth. It is defined as an angle between two planes, namely the vertical plane containing the horizontal projection of the bore axis, and the vertical plane containing the horizontal projection of the local earth magnetic field. In fig. 7, the angle A is that shown in connection with the toroidal fluxgate magnetometer. 3. The reference angle R is likewise an angle between two planes, namely a first plane containing the drilling axis and a line (usually called the scribe line) on the drill string parallel to the drilling axis, and a second plane containing the drilling axis and its vertical projection. The reference angle R is shown at the top of the unit in fig. 7.

Generally speaking, the sensor device of fig. 7:

1. A mechanical device with three axes to determine:

a) a vertical plane using gravity as a reference, b) a horizontal plane using gravity as a reference, and c) the north direction using the earth's magnetic field as a reference.

2. A motor-drive device for moving parts of mecha-

nism to desired positions about the axis.

3. Error converters to determine deviations from the desired positions about the axis and to provide feedback to the motor-drive device. 4. Control and measuring devices to measure the total motion signal when its sensitive axis is parallel to gravity (see Fig. 8, where the ordinate is the accelerometer output signal and the abscissa is the angle between the accelerometer's sensitive axis and the direction of gravity). A particularly accurate and desirable type of such a device is known to those skilled in the art as a force-balancing accelerometer, which is available in various versions. The output signal from the accelerometer 116 is transmitted via a motor operation control. 120

in the control section 121 to a step servo motor 122 which rotates the frame 100 until the accelerometer 116 reaches a zero position.

The accelerometer 116 is used to determine the reference angle R and will therefore be referred to as the reference accelerometer. In consideration of the previously stated definition of the reference angle R, a reference line must first be created parallel to the axis 102, and this reference line must be fixed in relation to the drill string or drill collar segment 26A. The reference line is identified as a scribe line 124 and is placed arbitrarily parallel to the axis 102. The angle R is thus equal to the angle between the scribe line 124 and the vertical plane containing the bore axis 102, i.e. the angle R is the angle between the scribe line and the "high side" of the hole as this expression is understood in drilling terminology. In the present invention, the printer line 124 can thus be represented by a light path.

In order to determine the angle R according to the present invention, the motor 122 on a signal from the control unit 121 will first drive the frame 100 and the accelerometer 116 to a "start" or "home" position where there are known angular relationships to the printer line 124. This home position is appropriate selected as coincident with the printer line 124 itself, and the achievement of this coincidence is determined photoelectrically using a light source 126 and a photocell 128. The light source 126 and the photocell 128

are shown mounted directly or indirectly on the support 114, but it should be understood that they can be mounted in any fixed manner relative to the drill string segment 26A. The light path 130 from the source 126 to the photocell 128 is defined in the plane by the printer line 124 and the axis of rotation 102 (the path 130 is thus equivalent to the printer line 124). Two rotatable disks 132 and 134 are located in the light path 130. Each of these disks has an opening 136 or 138, and the light beam 130 is interrupted except when the openings 136 and 138 are simultaneously aligned with the light beam for

to allow light to reach the photocell 128. The disk 132 is arranged directly on the shaft 106 (and is thus directly mounted on the first sway bar) and the disk 134 is mounted separately on a shaft 140 (the support for this is not shown for the sake of clarity) and is driven directly by a geared connection with the disk 132. The disk 132 allows the light to pass once for each revolution of the frame 100 and is dimensioned to allow the light to pass over an arc of approximately 12°. The disk 134 makes one revolution for every 30° of rotation of the frame 100 and is dimensioned to allow the light to pass over less than 1 degree of arc. The light from the light source 126 can thus only reach the photocell 128 once for each complete revolution of the frame 100, and then only in a band that is less than 1° wide. When the home position is reached, a first plane is defined by the printer line 124 (or light beam 130) and the axis 102.

When operation of the sensor device is initiated by a control signal from the digital filter 74, a signal is transmitted from the motor operation control 120 to the stepping motor 122, which has a driving connection with the shaft 106 via the gear exchange 142, and the motor 122 drives the frame 100 in a first direction of rotation (assumed to be counter-clockwise) until the light hits the photocell 128. The output signal from the photocell 128 is transferred to the control unit 121 to terminate the operation of the motor 122. This establishes the starting or home position for the reference accelerometer 116 for measuring the reference angle. Assuming that the accelerometer 116 is now in any position other than its zero position, the accelerometer, which can be considered as an error converter, will issue an output signal to the engine operation control unit 120 in the control section 121. The engine operation control unit 120 will then enter into operation to supply drive pulses to the motor 122 to cause rotation of the frame or sway bar 100 (clockwise or counter-clockwise) until the sensitive axis of the accelerometer 116 has reached a horizontal position, i.e. perpendicular to gravity, after which the output signal from the accelerometer 116 reaches a zero value and brings the operating control unit 120 to end the rotation of the wobble bracket 100. The sensitive axis of the accelerometer 116 defines in this zero position a vertical plane (another plane) which includes the axis 102. This second plane and the first plane, which is defined by the printer line and the axis 102,

are the planes between which the reference angle R is measured. Consequently, will

the net number and sign (corresponding to the direction of rotation) of equally long steps required to bring the step meter 122 to drive the accelerometer 116 from its home position to a zero position, and thus the net number of pulses delivered from the motor control unit 120, be a measure of the reference angle R. The pulse-shaped output signal from the motor control unit 120 is also transmitted to a binary up-down counter 144. The number of pulses counted by the counter 144 constitutes data or information corresponding to the reference angle R, and this data is finally transmitted to the surface of the well using mud-pulse techniques, so that the angle R is known at the surface of the well.

Another error-transforming accelerometer 148 is stationary mounted on another wobble bar having the form of a shaft 150 (with axis of rotation 151) which is rotatably supported on the first wobble bar 100 by bearings 152. This second accelerometer will occasionally be referred to as the inclination accelerometer . The sensitive axis of the inclination accelerometer 148 is arranged orthogonally with respect to it. sensitive axis of the reference accelerometer 116. The inclination accelerometer 148 establishes a vertical plane perpendicular to the plane established by the reference accelerometer 116, and it serves in cooperation with the reference accelerometer 116 to define a horizontal plane and to determine the inclination angle I of the drill axis 102 .

During operation of the inclination accelerometer 148, this is first brought to a starting or home position, which is an arbitrarily pre-selected and known position of the accelerometer and the shaft 150 with respect to the frame 100. The home position of the accelerometer is detected by means of an optical system similar to with the system used to detect the home position of the accelerometer 116. This optical system includes a light source 154, a photocell 156, a light path 158 and rotatable disks 160, 162 and 164 having openings 166, 168 and 170 respectively. The disk 164 is fixed mounted on a shaft 171, and the disc 160 has drive connection with a stepper servo motor 174 via a gear exchange as shown. The three discs are also drivably connected to each other by a gear exchange as shown. The gear exchange is dimensioned so that the disks run at slightly different rotational speeds in relation to the rotation of the wobble bracket 150. A preferred arrangement is that the disk 160 performs a full revolution for every 10° of rotation of the wobble bracket 150, while the disks 162 and 164 each -makes a complete revolution for each 9°<*>s and 8°"s of rotation of the wobble hoop 150, respectively. The openings 166, 168 and 170 line up only once for every 360° of rotation of the wobble hoop 150, always conforming will appear along the light path 158 once for every full 360° revolution of the wobble hoop 150, to allow the light beam to reach the photocell 156.

The use of three disks 160, 162 and 164 with slightly different revolutions is due to the fact that it is impractical to attach one of the disks directly to the wobble bracket 150 for the inclination measuring device. Had a. of the disks had been attached directly to the wobble bracket 150, a two-disk system could have been used as in the case of the reference angle system, where one of the disks is attached directly to the wobble bracket 100.

When operation of the tilt accelerometer is desired, its motor drive controller 172 supplies a signal to the stepper motor 174 to drive the motor in a first direction. Thus, the discs 160, 162 and 164 and the shaft 171 are rotated, and the shaft 171 drives via a spindle and gear 174 the wobble bracket 150 to rotate it about its axis in a first direction (presumably counter-clockwise). When the three openings 166, 168 and 170 reach the coincident position which allows the light beam to be transmitted to the photocell 156, the home position of the accelerometer 148 is reached, and the output signal from the photocell 156 is transmitted to the control section 121 to terminate the operation of the motor 174. The accelerometer 148 is located thus in a known position in relation to the frame or the sway bar 100.

Assuming the accelerometer 148 to be in an arbitrary position other than the position where the sensitive axis is perpendicular to the direction of gravity, the accelerometer 148 will act as an error converter, and error signals will be transmitted to the engine operation control unit 172 in the control section 121. the operating control unit 172 acts to generate output pulses which are delivered to a stepper motor 174 to drive this stepper for dirt in the direction that reduces the error signal. The swing arm 150 and the accelerometer 148 are thus driven in a series of steps until the sensitive axis of the accelerometer 148 becomes perpendicular to the direction of gravity, i.e. until the sensitive axis becomes a horizontal line, which defines another vertical plane established by the reference accelerometer. When the accelerometer 148 is in the zero position, further operation of the stepping motor is terminated.

In that the zero setting of the reference accelerometer 116 defines a first horizontal line (the sensitive axis of the accelerometer 116), and that the zero setting of the inclination accelerometer 148 defines another, likewise horizontal line (the sensitive axis of the accelerometer 148) which is orthogonal with respect to the first, these two orthogonal horizontal lines together define a horizontal plane, since a plane can be defined by two orthogonal lines or by a line and a direction. As this relationship is utilized in the present invention,

the horizontal line defined by the sensitive axis of one of the two accelerometers will define the direction of a plane that includes the horizontal line of the other accelerometer. Thus, however, the two sensitive 4 axes of the accelerometers 116 and 148 combine to define a horizontal plane.

The line of intersection between the first vertical plane (created at the sensitive axis of the accelerometer 116) and the second vertical plane (created at the sensitive axis of the accelerometer 148) becomes a vertical line that intersects the bore axis 102, and thus defines the angle of inclination I.

As in connection with the measurement of the reference angle R, the output pulses from the motor drive controller 172 are transmitted to a binary up-down counter 176. The net number of steps for the stepping motor 174 and thus the net number of pulses transmitted to the counter 176 and required to drive the accelerometer 148 to a zero position from the home position, is directly related to and is a measure of the inclination angle I of the drill axis 102 in relation to the vertical. The pulses counted by the counter 176 are finally transferred to the surface by the mud pulse-pulse-telemetry technique so that the angle of inclination I is known at the surface.

The sensor device also includes an azimuth sensor in the form of a ring core fluxgate magnetometer 178. The magnetometer 178 is of the same type as the magnetometer 58 which was described and discussed above in connection with fig. 4 for the rotation sensor. There is therefore no need for a detailed description of the properties of or the structure of the magnetometer 178. The magnetometer 178 is fixed on a shaft 180 which forms a rotating pendulum bracket in the sensor device. the shaft 183 for the shaft 180, and the bearing 182 is fixed to a rotatable shaft 184. The shaft 184 is parallel to the shaft 150 and rotatably arranged on the frame 100 by means of bearings 186 and is rotated about its axis by the shaft 171 via a worm gear 188. Thus the shaft 184 is slave-connected to the wobble bracket 150, which acts as a guide for it. The ring core of the magnetometer 178 is arranged perpendicular to the shaft 183 of the wobble bracket 180, and its axis is arranged perpendicular to the sensitive axis of the inclination accelerometer 148. When the reference accelerometer 116 and the inclination accelerometer 148 thus reach their horizontal or zero positions, the sway bar 180 is in a vertical position, and the ring core of the magnetometer 178 is in a horizontal plane.

The swing bracket 180 is turned about its axis via a pair of conical gears 190 and a worm drive 192. The worm wheel in the worm drive 192 and one of the conical gears 190 are connected to each other by a sleeve 191 rotatably arranged on the shaft 184. The worm drive is in turn driven by a shaft 194 which is connected to an azimuth servo motor 196. A photoelectric detection device similar to that described above with respect to the inclination sensor device is arranged to operate as shown between the azimuth servo motor 196 and the shaft 194. When this optical system is similar to that described above for the inclination sensor, further mention of it is unnecessary, and the components of this optical azimuth device are provided with numerical references corresponding to those in the optical inclination device, with the addition of the sign The optical device connected to the azimuth sensor, is also used to determine the starting or home position for the azimuth sensor 178.

The azimuth sensor is used to determine the north direction by sensing the local horizontal component of the earth's magnetic field. In a similar way to the reference and inclination sensors, the azimuth sensor is first driven to a start or home position which is a predetermined and known position, with the axis 183 perpendicular to the axis 102 of the drill string and with the sensitive axis of the magnetometer orthogonal to the axis 102 of the drill string as well as with the north-seeking axis of the magnetometer (the north-seeking axis is perpendicular to the sensitive axis) pointing in the direction of the drill bit (i.e. down - -in- the wellbore).

position by a signal emitted by the engine-drive control unit 198

and is transmitted to the azimuth servo motor 196 to turn the rocker arm 180 about its axis in a counter-clockwise direction until the home position is reached. The achievement of the home position is of course determined by the light beam 158<*>hitting the photocell 156', after which the output signal from this is transmitted to the control section 121 to end this first operation of the motor 196.

If the magnetometer 178 is assumed to be in an arbitrary position different from its zero position, an error signal is generated which results in operating signals from the motor drive control unit 198 to the stepper motor 196 to reduce the error signal generated by the magnetometer. The magnetometer 178 acts as an error converter, as the phase angle for the second harmonic in the output signal will increase and decrease depending on the direction of the sensitive axis in relation to the earth's magnetic field. The characteristic of this converter is that this phase angle change varies as a function of the sensitive axis orientation in relation to the earth's magnetic field, the variations being present as a maximum or minimum output signal when the sensitive axis coincides with the earth's magnetic field, and falls to zero when the sensitive axis is perpendicular to the earth's magnetic field. This relationship is shown in fig. 9. The magnetometer 178 acts as an error converter, in that the output signal will drop to zero when the magnetometer is moved to a position where the sensitive axis is perpendicular to the earth's magnetic field.

The error signal produced by the magnetometer 178, i.e. the output signal produced when the magnetometer is in a position different from the zero position, is transmitted to the motor drive unit 198 in the control section.121. On receipt of these error signals from the magnetometer 178, the motor drive unit 198 produces output pulses which are supplied to the stepping motor 196 to drive it step by step, so that the magnetometer 178 is turned to its position with a zero output signal, i.e. the zero position. The magnetometer 178 and its wobble bar 180 are thus operated in a series of steps until the sensitive axis of the magnetometer 178 is perpendicular to the direction of the earth's magnetic field, and further operation of the stepper motor is terminated.

The algebraic sum of the output pulses from the motor 198 and the motor drive control unit 172 is transferred via an OR gate device 199 to a binary up-down counter 200 in the control section 121. The OR gate device 199 consists of an OR gate 199a for sign signals and a OR gate 199b for digit signals. The net figure and sign of the aforementioned algebraic sum of pulses transmitted to the counter 200, and which is necessary to drive the magnetometer to the zero position from the home position, is a direct measure of the direction of the well axis with respect to magnetic north, i.e. the angle A. The pulses from the motors 198 and 172 must be added algebraically because the wobble bar 183 is both driven by its own motor 196 and also rotated one step for each step by the motor 174, the shaft 171 driving the accelerometer 148 to its zero position due to the drive connection between the shafts 171 and 184 gear pair 190. The pulses that are counted by the counter 200 are finally transferred to the surface by mud pulse telemetry technique so that the azimuth angle A is known at the surface.

The sensor device described above thus consists of three sway bars that are servo-controlled by means of two error-converting accelerometers and an error-converting magnetometer. The accelerometers are used to create horizontal and vertical planes by searching for positions with zero gravity along two orthogonal axes, and the magnetometer is used to determine the direction magnetic north in the horizontal plane. The device measures the reference angle R, the inclination angle I and the azimuth angle A, these three forms of angular information being sufficient to define the position and direction of the drill string at the bottom of the well.

It should of course be understood that for each of the three sensors, namely the accelerometer 116, the accelerometer 148 and the magnetometer 178, electrical input signals are needed, so that these sensors can act as error converters to produce output signals which are transmitted to their respective motor drive control units. These electrical input signals can be supplied in any known and desired manner (including slip rings) from a generator 65, and in fig. 7, they are only shown schematically as VQ.

A particular advantage of the sensor device according to the present invention is that it eliminates the need for separate angle converters and the associated mechanical and reliability problems that such angle converters typically exhibit. Instead of such angle converters, angle measurements according to the present invention are only carried out by counting the net number of steps at the step motor or the net number of pulses transferred to the step motor for the execution of the individual steps. The drive transmissions from stepper motors are very precise, so each step of a stepper motor results in a known angular displacement of its associated wobble bar. Thus angle measurement is reduced to a simple process of algebraic counting of pulses delivered to or steps performed by the stepping motor.

The entire sensor mechanism in fig. 7 can be immersed in a thick liquid silicone oil which completely fills the sensor housing 44. The oil serves both to protect the sensor mechanism from being damaged by vibrations and shocks and to lubricate bearings and transmissions, while also acting as a heat transfer medium for the motors.

To protect the sensitive precision gear sets that drive the wobble rings 150 and 180 in the shaft 184 from the effects of differences in thermal expansion, the worms in the transmission links 174, 188 and 192 are isolated by means of expansion bellows 202 and symmetrically supported in hangers 204 made in one piece. Thus, shafts 171 and 194 are in reality shaft sections which

are joined together by means of the expansion bellows 202, which reliably transmit the turning movement of the axles, while they absorb any thermal expansion of the axles in both directions, so there will be no displacement of the contact points between cooperating wheels in the transmission joints.

If cables are used for the electrical input and/or output signals for the accelerometers, it is necessary to use safety limit switches. Thus, a mechanical stop device 206 will be arranged in connection with the sway bar 150

which extends from the wobble bar 100 and is positioned so that it is touched by a finger 208 secured to the wobble bar 150. The finger 208 and the stop means 206 in combination limit the rotation of the wobble bar 150 to less than 360° in which

any direction and thus prevents damage to the electrical cables. Similar measures could also be used for the other sway bars if the circumstances warrant this.

Reference should now be made to figures 10 and 11, which respectively show a block diagram and a connection diagram of the control device according to the invention. Fig. 10 is a block diagram of the entire control device, which includes the rotation sensor circuit of Fig. 5 and the motor operation control units 120, 172 and 198 for the measuring circuit for the reference angle, the measuring circuit for the inclination angle and the measuring circuit for the azimuth angle, respectively. The motor operation controllers 120 and 172 are similar, while the motor controller 198 differs only in that some of the components at the beginning of the circuit are different because the azimuth error signals are derived from the magnetometer 178, while the reference and inclination signals are derived from the error-transforming accelerometers 116 and 148. The form on

fig. 11 shows one of the two identical engine operation control units 120 and 127, and the deviating structure that occurs in the engine operation control unit 198 will be pointed out in the following.

In fig. 10, the rotation sensor is seen, which includes the magnetometer 58, the detector 70 (composed of the phase detector 70A, the low-pass filter 70B and the amplifier 70C), the zero level detector 72 and the digital filter 74 (composed of the clock 76, the comparator 78 and the rocker 77, see fig. 5A).

As described above in connection with fig. 5 and 6, the sensing of the condition of no rotation (or a predetermined low rotation rate) of the drill string will result in the toggle 77 being set. The rising edge of the Q output signal from the flip-flop 77 is transferred to an initiating control circuit 210 to conditionally adapt and start the operation of the control unit 121. The initiating control unit 210 (see Fig. 12) is built up of two single-pulse multivibrators 212 and 214. The rising edge of the Q output signal from the flip-flop 77 triggers the multivibrator 212 to produce a pulse of duration 1 ms at the Q output of the multivibrator 212.

This output pulse at the Q output of the multivibrator 212 is a ready pulse (READY.P) which, as will be described below, is transmitted to the reset side of several organs in the control system to ensure that the entire control system 121

is prepared for a start command. The Q output from the multivibrator 212 is connected to the input of the multivibrator 214 so that the multivibrator 214 is triggered at the trailing edge of the pulse from the multivibrator 212 to produce a pulse with a duration of 1 ms, which serves as a start command (STARTP) for the device. Like that

will also be described in the following, the start command is transmitted to various components of the control system to initiate its operation.

In addition to the start pulse that is transmitted to various components of the system, a master clock also supplies 216 timing pulses or timing signals to the control system. As shown in fig. 13, the master clock 216 includes a free-running astable multivibrator 218, whose output signals are transmitted to a frequency-dividing counter 220 which divides the frequency of the multivibrator output signal to provide reference timing pulses for transmission to various components of the system. Fig. 13A shows the multivibrator output signal or.. frequency (f) and output pulses CP1-CP10 from master clock 216 which are transmitted to various components of the system for timing purposes.

The control device will now be described in connection with the determination of the reference angle R. It should be understood that the same description can be used for the inclination angle I and,

with exceptions that will otherwise be stated, also in connection with the azimuth angle A. The description will be presented with common reference to fig. 10 and 11. The terms "high", "up" and "logic 1", which denote states of the system components, shall be understood to be equivalent in the same way as the terms "low", "down" and "logic 0".

HOME- MODE- OPERATION

When the initiating control circuit 210 is triggered, the clearance pulse (CLARERP) will be transmitted to several components in the start/stop/run circuit of the pulse generator and control unit 222. The pulse generator and control unit 222 includes a start circuit

224 (fig. 11B) - which has a home subcircuit 226 and a measure subcircuit 228 - a run circuit 230, a finish circuit 232 and a stop circuit 234 (fig. 11C).

Reference is first made to the starting circuit 224 in fig. 11. A clearance pulse (CLARERP) from the initiating control unit 210

(Fig. 10B) is transferred to an OR gate 236 (Fig. 11B) and passes through the OR gate to a D-type flip-flop 238 to reset it. The rocker 238 may also sometimes be referred to as the "home" rocker because it is important in determining the "home" position to which the reference accelerometer 116 is first driven, as described above. The start pulse (STARTP) from the control unit 210 is then transferred to an OR gate 240 (Fig. 11B) and passes through the OR gate 240 to the flip-flop 238, and is transferred

also to another OR gate 244. The start pulse is inverted on arrival at the flip-flop 238, and the trailing edge. of the start pulse will therefore set flip-flop 238, as a D-type flip-flop requires a rising signal to set. When the flip-flop 238 is set, the Q output will assume a high level and constitute a signal which will be designated in part as HOME MEF. The set state of the toggle 238 constitutes the home mode. The Q function (HOME MEF) of the rocker 238 is delivered to various locations in the device. First, the HOME MEF signal is supplied to a one-pulse multivibrator 242 in the home circuit 226, but it does not trigger the multivibrator 242 until the trailing edge of the home signal occurs, which occurs later in the operation of the device when the accelerometer 116 is brought to its home position. The pulse HOME is also supplied to a magnitude-detecting circuit 246 in a sign- and magnitude-sensing detector 245, and more particularly to an OR gate 247 in a magnitude-detecting circuit 246 (Fig. 11A). This HOME MEF signal takes precedence over any other signal to the OR circuit 247 and is passed to an AND gate 249 to form one of two inputs to it. When the second input signal arrives at the AND gate 249 together with the HOME signal, pulses will be generated to drive the reference accelerometer to its home position.

The second input signal to the AND gate 249 is supplied from the drive circuit 230 (Fig. 11C) which has received an input signal from the OR gate 244 (Fig. 11B). The input signal from the OR gate 244 is due to the pulse STARTP which passes through the gate 244, and appears at the output of the gate 244 as a drive signal (RUN), which is then transferred to the S input of a JK-type flip-flop 248 in the drive circuit 230. The flip-flop 248 (partially referred to as the "run" flip-flop) was previously reset by the clearance pulse CLARERP from the initiating control unit 210, so that the RUN signal at the S-terminal of the flip-flop 248 without condition adaptation sets . the flip-flop 248 so that the Q output signal will be at a high level and will be transferred to the AND gate 249 as the second input signal thereto. When the necessary two input signals to the AND gate 249 are present, an output signal is supplied from the AND gate 249 to the D input of a D-type flip-flop 250 in the pulse generator circuit 252. The C input of the flip-flop 250 receives clock pulses CP1 from the main clock 216, and the rocker 250 are set

(D input signal transferred to Q) when the signal on the D input is at logic level "1" (input signal from port 24 9)

in the presence of the clock pulses CP1. Thus the rocker is set to 250

with a frequency determined by the clock pulses CP1 when the input D is at logic level "1". At each setting of the flip-flop 250, the Q output signal is transferred to an AND gate 254 in the pulse generator 2 52, where it is gate-controlled with another signal CP3 from the main clock 216. The two input signals to the AND gate 254 result in a pulse-shaped output signal from it. This pulse-shaped output signal is transmitted to various places in the device, including the motor sequence circuit 256 of the drive motor 122. The output signal from the AND gate 254, and thus the output signal from the pulse generator 252 is thus a train of step pulses transmitted to the motor sequence circuit..

The HOME MEF signal (which occurs when the Q output from flip-flop 238 (FIG. 11B) is high) is also transferred to the S input of a JK-type flip-flop 258 in the sign and magnitude detector 245. The HOME MEF signal on the S input of flip-flop 258 sets this so that the Q output signal becomes high. The high Q output signal from the flip-flop 258 is also transmitted to the motor sequencer circuit 256, where it constitutes and serves as a sign and direction message to cause motor rotation in a predetermined direction (presumably counter-clockwise) to drive the reference accelerometer 116 to its home position.

From the foregoing, it can be seen that two separate signals are transmitted to the motor sequence circuit 256. One of these signals is the step pulses from the pulse generator 252, and the other is the sign and direction signals from the flip-flop 258 in the sign and magnitude detector 24 5.

The motor sequencer 256 is a two-bit up/down counter 260. It receives the step pulses from the pulse generator 252 and sign information from the flip-flop 258 in the sign/magnitude detector 245 and converts these input signals into a four-phase signal. That is the motor frequency circuit is a phase generator for a four-phase motor. The four phase signal is transmitted on separate lines to a motor drive amplifier 262 which has various amplifiers and level converters for converting the four phase signals from the sequence circuit 256

to a suitable power level for operation of the four-phase stepper motor 122. Before the individual phases are supplied to separate amplifiers'i

the drive motor amplifier 262, each phase is separately transferred to an AND gate 261, whose other or activating input signal is the Q output signal from the flip-flop 77 of the digital filter 74

(Fig. 10B). Thus, the drive motor 122 will not be put into operation unless there is both a signal for no rotation from the digital filter 74 and pulses from the pulse generator 252. In the presence of both signals to each AND port 261, the reference accelerometer is driven towards its home position and the attention should be drawn to the fact that the direction of rotation towards the home position is always the same (assumed to be anti-clockwise), as the sign or direction information from the rocker 258 is always at the same level home mode operation.

The motor 122 runs until the home detector 128 receives light from the light source 126. Light falling on the home detector 128 is amplified and converted to logic levels in an amplifier and rectangle shaper circuit 264 (FIG. 11C), the output of which is transferred to the other input of an AND gate 266 in the stop circuit 234. The first input signal to the AND gate 266 is already present in the form of HJEMMEF signals from the flip-flop 238 in the start circuit 224. The output signal from the AND gate 266 assumes a high level during the transfer of the signal from the amplifier and rectangle shaper circuit 264, and this output signal is transferred to and passes through an OR gate 268 which causes the output signal from the OR gate 268 to assume a high level. This resulting signal from the OR gate 268 is transferred to an AND gate 270 in the drive circuit 230, where the gate is controlled with the clock signal CP9. The output signal from AND gate 270 is inverted and transferred to the C input of JK-type flip-flop 248 to reset it at the trailing edge of signal CP9 and thereby cause the Q output signal from flip-flop 248 to assume a low level. This resetting of the flip-flop 248 removes one of the two input signals to the AND gate 249 of the magnitude detection circuit 246, whereby the D input signal to the flip-flop 250 is removed so that it is reset and no more pulses are generated from the pulse generator 252, whereby the motor 122 stops because the predetermined home position has been reached.

The home mode operation described above takes place simultaneously for all three axes, i.e. for reference, inclination and azimuth. Each of the motor control circuits 120, 172 and 198 has a drive flip-flop 248. The Q output signal from each drive flip-flop 248 is connected to an AND gate 272 with three inputs in a common "done" circuit 232. When one of the three drive flip-flops 248 is reset, its Q output will assume a high level. When the Q output signal from each of the three flip-flops 248 is at a high level, the output signal from the AND gate 272 will assume a high level to constitute a done signal indicating that the accelerometers 116 and 148

and the magnetometer 178 have all been moved to their respective home positions. This completion signal at the output from gate 272 is transmitted as one of the input signals to an AND gate 274 in the home sub-circuit 226 in the start circuit 224 (Fig. 11B). The other input signal to the AND gate 274 is provided by the HJEMMEF signal, and when both signals occur, a signal thus passes through the AND gate 274 and is transmitted to the AND gate 236. The signal passes through the AND gate 236 and is applied to the R input of rocker switch 238 to reset this. When the flip-flop 238 is reset, its Q output assumes a logic "0" and causes the one-pulse multivibrator 24 2 to be active for 1 ms, ie, the multivibrator 24 2 is triggered on the trailing edge of the HJEMMEF signal. The output pulse with a duration of 1 ms from the multivibrator 242 is supplied to an up/down counter 144 to reset it so that the counter 144 is now made ready to receive measuring pulses. The pulse-shaped

• output signal from the multivibrator 24 2 also causes a pulse to pass through the OR gate 244, whereby the DRIVE pulse again occurs at the output of the gate 244 and is transmitted to reset the flip-flop 248 in the drive circuit 230 (Fig. 11C) in the same way as flip 248 was set during home mode operation. When the flip-flop 248 is set, the Q output signal will assume a high value and again be transferred to the AND gate 249 of the magnitude detector circuit 246 to condition the AND gate 249 (Fig. 11A). However, it should be noted that the HOME MEF signal is removed in this mode of operation, and thus no signal passes through the AND gate 249 until the OR gate 247 receives an input signal from some part of the circuit in the sign and magnitude detector 245 The transmission of the done signal from gate 272 thus terminates the HOME signal in each of the motor control circuits 120, 172 and 198, whereby the pulse generator output signal is temporarily suspended to await further activation even though the Q output signal from the drive flip-flop 248 is at high level and is

transmitted as one of the input signals to the AND gate 24 9. Home mode operation is thus completed.

MEASUREMENT - MODE - OPERATION

The pulse from the single-pulse multivibrator 24 2 is also inverted and applied to the C input of a D-type flip-flop 276, which is set at the trailing edge of this pulse. The Q output from the flip-flop 276

then assumes a high level, which constitutes a measurement signal and is transmitted i.a. as the first input signal to an AND gate 278 in the stop circuit 234 (Fig. 11C). The gates 278 and 266 and 268 of the stop circuit 234

are connected to form an AND/OR gate device. The measurement signal is also transferred to the D input of a D-type flip-flop 310 to set it. The device is now set for operation in a measurement mode as determined by error signals from the accelerometer 116.

It is now assumed that the reference accelerometer 116 is located

in an arbitrary position different from the zero position, an error signal will be produced which is transmitted to the amplifier 280

(Fig. 11A). As shown in fig. 8, this signal is a current with a form of a cosine function of the angle between the sensitive axis of the accelerometer and the direction of the gravitational force. The amplifier 280 is a power amplifier of the LM107 type, and the amplifier coupling

can be found described in the Linear Applications Handbook, 1973, by M. K. Vånder Kooi,. National Semiconductor Application Note AN20-5, February 1969, fig. 13. In this amplifier circuit, the current is amplified and transformed into a voltage for further use in the device.

The amplified signal from the amplifier circuit 280 is then supplied to a filter circuit 282 for removing high frequency components that may have entered the signal from the stepping motor and vibrations in the surroundings. The filter is a two-pole filter with a cut-off frequency of 3 Hz and with an amplifier of the type LM107, and can be found described in the Linear Applications Handbook, 1973, by M. K. Vånder Kooi, National Semiconductor, Inc. Note AN5-10, April 19 68 , fig. 25.

The filtered signal from the filter circuit 282 is supplied and integrated in an integrator circuit 284. The amplifier in the integrator circuit 284 is of the type LM107, the switches S1 and are semiconductor switches, e.g. RCA CD4016, and for further details regarding such integrator circuits reference may be made to Operational Amplifiers, Design and Applications, by Tobey, Graeme and Hunlsman, fig. 6.15, McGraw-Hill, 1971. The integrator operates to magnify the error from the accelerometer 116 as a function of time to investigate and process small errors. The integrator is reset by feeding the output signal from the pulse generator 252 back to the semiconductor switches and S~ to reset the integrator to zero by alternately closing and opening the switches and S 2 with sig-

nal from the pulse generator each time the stepping motor 122 takes a step, one switch being opened when the other is closed.

The filtered signal from the filter 282 and the integrated signal from the integrator 284 are both supplied to a summing circuit 286, where they are added algebraically. Even if the error signal from the filter 282 is small, the integrated error signal will thus be available for processing in the rest of the device. For further information on the summing circuit, reference is made to National Semiconductor, Inc. Note A and 20-3, February 1969, fig. 3 (Linear Applications Handbook, 1973 published by M. K. Vånder Kooi). The output signal from the summing circuit 286 is then applied to the sign and magnitude detector circuit 245 to be examined for both sign and magnitude. The magnitude corresponds to the degree or magnitude of the deviation between the measured position of the reference accelerometer and the zero position, and the sign corresponds to the direction of rotation required to move the reference accelerometer to the zero position.

The sign and magnitude detector circuit 245 has a first comparison circuit 288A and a second comparison circuit 288B. Comparator circuit 288A has a voltage divider 290 composed of resistors RIA and R2A, connected as shown to an amplifier 292, and comparator circuit 288B has a similar voltage divider 294 composed of resistors R1B and R2B, connected as shown to an amplifier 296. Amplifiers 292 and 296 are both power-differential amplifiers. The output signal from the summing circuit 286 is applied to the amplifier 292, and the same output signal is also applied to the amplifier 296. The voltage divider 290 creates a first reference voltage, reference A, for the differential amplifier 292, and the voltage divider 294 creates a second reference voltage, reference B, for the differential amplifier 296. The comparison circuit works to compare the output signal from the summing amplifier 286 with the reference voltages. As will be seen from fig. 14A, 14B and 14C, the output signal (UT A) from the amplifier 292 will be negative when the output signal from the summing circuit 286 is more negative than the reference voltage A. Similarly, the output signal (UT B) from the amplifier 296 will be positive when the output signal from the summing amplifier 286 is more negative than the voltage level of the reference B. As a result of this operation of the comparison circuits 288A and 288B, signals UT A and UT B appear, as shown in FIG. 14B and 14C.

The output signals from the comparison circuits 288A and 288B are supplied respectively to an inverting buffer 298 and a non-inverting buffer 300. The buffers serve to change the level that the voltages from the comparison circuits have to a voltage level compatible with the flip-flop 258 to which the buffer output signals are applied. The signal UT A (shown in Fig. 14D) is supplied to the J terminal of the flip-flop 258, while the signal UT B is supplied to the K terminal of the same flip-flop. The output signal from the buffers 298 and 300 is also supplied to the OR gate 247, as this is located in the size detector circuit 246. Thus, the signals UT B and UT A (see Fig. 14E) are supplied to the OR circuit 247.

Reference is again made to the flip-flop 258. The time control pulses CP1 are transferred from the main clock 216 to the C input, whereby the signals UT A on the J input and UT B on the K input that are present when a time control pulse CP1 is received will be supplied to the flip-flop. From the signal diagrams 14B-14E, it can thus be seen that the rocker 258

in the presence of off clock pulses CP1 will be set (Q output high) when UT A is negative (UT A positive), and will be reset (Q output low) when UT B is positive. Considering that the Q output signal from the flip-flop 258 is applied to the motor sequencer circuit 256 to control the direction of rotation of the motor 122 depending on the level of the Q output signal from the flip-flop 258, it can be seen that the motor 122 will be driven either clockwise or counterclockwise depending on the output signals from comparator circuits 288A and 288B. Thus, the reference accelerometer 116 is driven in the correct direction to reduce its emitted error signal and is brought to its zero position.

The OUT A signal (inverted to OUT A) and the OUT B signal applied to the OR circuit 247 in the magnitude detector circuit 246 serve to determine the magnitude of the signal from the accelerometer 116. As illustrated by the signal diagrams 14A-14E, the signal from the summing circuit 286 , when UT B or UT A is at a high level, be outside the limits indicated in fig. 14A, i.e. below the reference A and above the reference B. Thus, the area below the reference A and above the reference B in fig. 14A define a zero band, and when the error exceeds this zero band, i.e. comes above the reference A or below the reference B, a signal will be passed through the OR gate 247 and supplied to the AND gate 24 9 as the second input signal thereto. The first input signal to the AND gate 249 is already present in the form of the high Q output signal from the drive flip-flop 248 (Fig. 11C). Thus, in the manner described above, a signal will be passed through the AND gate 249 to set the flip-flop 250, the flip-flop being set when the D input signal is at logic "1" in the presence of clock pulses CP1. As described earlier in connection with the home mode operation, the set Q output of the flip-flop 250 is then gate controlled with clock pulses CP3 in the AND gate 254, whereby the motor sequence circuit 256 is supplied with step pulses for gate control with the high Q output signal from the flip-flop 77 at the gate 261 to drive the motor 122. The motor 122 will continue to rotate as long as it receives step pulses from the pulse generator 252, i.e. until the accelerometer 116 is brought to its zero position, where the output signal from the summing circuit 282 corresponds to the zero signal as described above.

The output signals from the flip-flop 258 in the sign and magnitude detector circuit 245 and the pulse-shaped output signals from the pulse generator. 252 are also both applied to the up/down counter 144 (FIG. 11B) for algebraic summation to determine the net number of step pulses applied to the motor 122 to drive the accelerometer 116 to its zero position.

As will be seen, the signal diagrams of fig. 14A-14E shown by way of illustration only. They provide an approximate picture of a condition where the accelerometer 116 would actually swing or oscillate back and forth about its zero position. For other conditions with occurring errors, there will be an UT A or UT B signal, but this would not occur at regular time points.

As described above, the drive flip-flop 248 (Fig. 11C) was reset by the transfer of a signal from the stop circuit 234 to the drive circuit gate 270 in the presence of clock pulse CP9 at the gate 270. As also previously described, the signal from the stop circuit 234 occurred when where at the same time a signal from the home detector 128 (through the amplifier and rectangle shaper circuit 264) and the HJEMMEF signal from the flip-flop 238 were supplied to the gate. In the measurement mode, the signal HJEMMEF is brought to an end, and the signal from the stop circuit 234, which serves to reset the drive flip-flop 248 , must therefore be produced in another way. In the measuring mode, the flip-flop 276 in the measuring circuit 228 is set so that the signal MEASURE is supplied as a first input signal to the AND gate 278 in the stop circuit 234. When there is also another input signal to the AND gate 278, a signal will be transmitted through the AND- gate 278 and through the OR gate 268 to be supplied to the AND gate 270, whereby the drive flip-flop 248 will be reset when a clock pulse CP9 occurs at the same time. This second input signal to the AND gate 278 is supplied from a counter 302 which emits a signal to the AND gate 278 when it has exceeded its capacity.

There are two ways to introduce pulses into the counter 302. First, the Q output signal from the flip-flop 258 will change between high and "low" if a sign change occurs in the sign and magnitude detector circuit. The Q output of the flip-flop 258 is connected as one of the inputs to an AND gate 304, the other input of which is connected to the Q output of a flip-flop 306. The flip-flop 306 has been reset by the drive pulse, so that its Q output is at high level, and there will thus pass a signal through the AND gate 304 every time the Q output signal from the flip-flop 258 assumes a high level in accordance with a sign change. The output signal from the gate 304 passes through an OR gate 308 and is supplied to the counter 302. When the counter 302 exceeds its capacity, a signal is delivered from the counter 302 to the AND gate 278 which coincides with the TARGET signal to the gate 278, whereby it releases a signal to the OR gate 268 and hence to gate 270. The signal which is thus supplied to gate 270 will, in the presence of the clock pulses CP9, reset flip-flop 248, whereby the Q input signal from flip-flop 248 to gate 249 in the size detector circuit is removed. Removal of the input signal to gate 249 terminates the operation of pulse generator 252, thereby breaking the step coupling of motor 122. Thus, the step coupling of the motor 122 can be interrupted

in a "sign forced" stop mode when the sign of the error signal from the accelerometer 116 changes a set number of times. This would of course occur when the accelerometer 116 has reached its zero position and swings back and forth about it.

The flip-flop 248 can also be reset to interrupt the step coupling of the motor 122 if no pulses are generated by the pulse generator 252 for a fixed time interval. This condition, which can be termed a "time-forced" stop mode, is carried out by means of the D-type flip-flop 306 (described above) and flip-flop 310 of type D. The TARGET signal from flip-flop 276 is applied to the D input of flip-flop 310 to condition it. Also, a timing stop signal CPN (a derivative of the master clock output signal) is applied to the C input of the flip-flop 310 to time it, and the R terminal of the flip-flop 310 is connected to receive the output pulses from the pulse generator 252. The flip-flop 310 will be set every each time a "zero" to "one" transfer is received on clock input terminal C, and be reset each time a pulse is received on terminal R from pulse generator 252. Companion flip-flop 306 is reset once at the beginning of the measure mode by the run signal supplied to the R terminal. The C terminal of flip-flop 306 is also connected to receive the CPN signal from the master clock, and flip-flop 306 will be set at the leading edge of the signal CPN if the conditional D input of flip-flop 306 is high, a condition which occurs if the flip-flop 310 is set when the flip-flop 306 receives the leading edge of the signal CPN. When the flip-flop 306 is set, it supplies one of the input signals to an AND gate 312, the other input signal of which is constituted by pulses CP1

from the main clock. The pulses CP1 are thus passed through gate 312 and through gate 308 to counter 302. A train of pulses is thus fed to counter 302 to cause it to exceed its capacity, whereby a signal is passed through gate 278 and through gate 268 to be delivered to gate 270. The signal thus supplied to gate 270 coincides with the clock input signal CP9 to reset the flip-flop 248, whereby the gate 249 is brought into the blocking state and the output signal from the pulse generator 252 is interrupted. Thus, the stepping coupling of the motor 122 is terminated because the accelerometer 116 is in its zero position.

The Q output of the flip-flop 248 is connected to the gate 272 of the "done" circuit 23 2. When the flip-flop 248 is reset on termination

of the operation of the motor 122, the Q signal will be applied to the gate

272. When the Q signals are similarly applied to port 272 from all three axes (ie the corresponding "drive" flip-flops) and all three flip-flops

are reset to terminate operation of their respective motors, a "done" signal will be sent through gate 272 and output to gate 274 of home section circuit 226 and also to a third input terminal at AND gate 314 of measure section circuit 228. One of the three terminals of the AND gate 314 also receives the TARGET signal, so that the gate receives two of the three input signals needed to let a signal through. A first pass through

flip-flop 316 of the JK type in measuring circuit 228 has previously been set by the signal CLARERP, so the Q output signal from flip-flop 316 is at a high level. The Q output from the flip-flop 316 is connected as the third input to the gate 314, whereby the "done" signal from the gate 272 will pass through the gate 314 if this is the first time the done signal occurs since the reception of the start pulse STARTP. The signal released through the AND gate 314 passes through the OR gate 318 and is supplied to the R input of the flip-flop 276

to reset this and thus interrupt the TARGET signal. When flip-flop 276 is reset, the trailing edge of the TARGET signal triggers a monostable charge multivibrator 320 so that it produces a pulse of duration 1 ms, denoted LOADP. The LOADP signal is supplied to a shift register 331 to prepare the stowage inputs of the shift register in operation, whereby the information stored in each of the up/down counters 144, 176 and 200 is transferred in parallel to the shift register. The pulse LOADP is also applied to flip-flop 316 to reset it and is also passed through OR gate 240 to set flip-flop 238. The LOADP pulse passing through OR gate 240 is also applied to OR gate 244 to produce a . other drive pulse. This run pulse again sets the run flip-flop 248 to bring the device back into the home mode as described earlier.

Thus, the control device will repeatedly

run cycles of home-mode and measure-mode operation until operation of the control device ends when rotation of the drill string resumes. The repeated cycle of home mode and measurement mode operation will be as described above, except that the rocker 276

will not be reset on the subsequent run-through of the system at the "done" signal from gate 272, as the pulse LOADP will have reset flip-flop 316 to produce a logic

"0" on the Q output from gate 316 to thereby remove one of the necessary input signals to gate 314. In these subsequent

ing run-throughs of the system, the flip-flop 216 will be reset only on receipt of a done signal (DONE P) which comes from a shift pulse generator 330 and is applied to the OR gate 318. Operation of the shift pulse generator is initiated by the LOADP pulse.

The first grind-through flip-flop 316 is necessary in the device because the shift pulse generator 330 does not become active until the first system cycle is completed. A one-off time pulse is therefore needed to run the system through again, so that a new set of measurements can be taken while the first information entered into the shift register at the first LOADP signal is transferred to the surface. This shift pulse generator, which is only a frequency divider for frequency division of the main clock pulses, generates pulses that serve to move the information out of the shift register 331 to the valve driver 57 which acts on the piston 56. The FERDIFP signal is generated each time after every n number of pulses from the pulse generator, corresponding to the storage capacity of the shift register 331.

As stated previously, the above description applied to the motor drive control 120, and the same description will also apply to the corresponding unit 172. The motor drive control unit 198 differs only in that the amplifier 280 and the filter 282 have been replaced with a unit similar to the detector 70 (including the phase detector 70A, filter 70B and amplifier 70C) to receive and process the output signal from the magnetometer 178. The output signal from the detector 70 in the engine operation control unit 198 is fed to the associated integrator, and the entire rest of the unit 198 is matched to and operated in the same manner as the engine operation control unit 120. A different set of clock pulses is supplied and used in each of the three motor control units 120, 172 and 198 so that these are driven in turn in their measurement mode to be driven simultaneously, which could result in crosstalk or interference in signals from the three units. That is that the reference motor 122 is brought forward one step, after which the inclination motor 174 is brought forward one step, and then the azimuth motor 196 a corresponding step, and that this sequence of steps is repeated until all three sensors have reached their zero positions.

Each LOADP pulse is also applied to the S input of the flip-flop 78 (see Fig. 5A) to set it, whereby the Q output signal from the flip-flop 78 assumes a high value and constitutes one of the necessary input signals for the AND gate 79. The other input signal for the AND gate 79 is the inverted Q output signal from the flip-flop 76. Thus, the AND gate 79 will release a signal when the flip-flop 76

is set (corresponding to a restored turning condition) and the LOADP signal is generated. This signal is passed through

at AND gate 79, brings the AND input to flip-flop 77 high, whereby a rising edge of the clock pulse CPN will reset flip-flop 77 so that the Q output thereof assumes a low value (level X in Fig. 6C) to report a return to the turning mode. The repetition of this low state of the Q output signal from the flip-flop 77 then interrupts the operation of the stepper motors 122, 174 and 196 by removing one of the input signals to the AND gate 261 of each motor driver circuit 256 and also by activating the piston driver 57.

The above-described run-through of home and measurement modes

will then continue for each of the reference, inclination and azimuth magnetometers 1116, 148 and 178 respectively until the rotary sensor logic senses drill string movement or the energy supply is removed from the system in the absence of generator power, which e.g. can occur when the mud flow is stopped.

Although preferred embodiments have been shown and described, it should be understood that various modifications and replacements can be made to these without deviating from the idea and scope of the invention. The description of the present invention shall thus serve to illuminate it and is not to be understood as limiting.

Claims (36)

1. Sensing device for periodically sensing directional parameters for a drill string in a borehole, and for generating output signals that are in accordance with the measured parameters, and which are to be transmitted to the surface, characterized in that the sensing device comprises a three-axis oscillating hoop with first organs that respond to gravity to determine a vertical plane and a horizontal plane and with other organs that respond to magnetism to determine the setting relative to the direction of the earth's magnetic field, a motor-drive device to move the first and second members from first predetermined positions to second predetermined positions, each of the other positions having a predetermined setting with respect to the direction of gravity and the direction of the earth's magnetic field respectively, a control device for controlling the operation of the motor-drive device and for measuring the total movement of each of the first and second bodies between the first and second positions. 2. Sensing device as specified in claim 1, characterized in that the three-axis wobble hoop is mounted in a segment of the drill string and comprises a first wobble hoop which is rotatable about the axis of the drill string segment or an axis parallel to this, a second wobble hoop which is rotatable about a axis perpendicular to the rotation axis of the first wobble bar, and a third wobble bar which is rotatable about an axis perpendicular to the rotation axis of the second wobble bar. 3. Sensing device as stated in claim 2, characterized in that the second wobble hoop is rotatably arranged in the first wobble hoop and that the third wobble hoop is rotatably arranged on a shaft which in turn is rotatably arranged in the first wobble hoop, the rotation axis of the third wobble hoop is perpendicular to the axis of rotation of the shaft, while the last-mentioned axis of rotation is parallel to the axis of rotation of the other sway bar. 4. Sensing device as set forth in one of claims 1-3, characterized in that the first organs that react to the force of gravity comprise a first error-transformation accelerometer arranged on the first wobble bar and a second error-transformation accelerometer arranged on the second wobble bar, each of the misalignment accelerometers have a sensitive axis with respect to the direction of gravity, and that the misalignment accelerometers are arranged in such a way that the sensitive axis of the first accelerometer is perpendicular to the axis of the drill string in the second position, and that the sensitive axis of the second accelerometer is perpendicular to the sensitive axis of the first accelerometer in the second position of each accelerometer. 5. Sensing device as set forth in one of claims 1-3, characterized in that the other devices that respond to magnetism are a flux gate magnetometer arranged on the third wobble bar and made with a sensitive axis with respect to the direction of the earth's magnetic field, the magnetometer is arranged in such a way that its sensitive axis is perpendicular to the direction of the earth's magnetic field in the second position of the magnetometer. 6. Sensor as specified in claim 1, 4 or 5, characterized in that the movement of the first accelerometer corresponds to a reference angle formed between a first plane containing the axis of the drill string and a known reference on the drill string, and another plane containing the drill axis and a vertical projection of this, that the displacement of the second accelerometer corresponds to the angle of inclination of the axis of the drill string with respect to the vertical in a common plane, and where the movement of the magnetometer corresponds to the azimuth angle between a vertical plane containing the horizontal projection of the axis of the drill string, and the vertical plane containing the horizontal projection of the direction of the local earth magnetic field. 7. Sensory organ as specified in one of the preceding claims, characterized in that each of the organs that react to gravity and magnetism has a light source attached to it, a photoelectric receiver and light control means for transmitting light from the light source to the photoelectric receiver when the respective means responsive to gravity or magnetism are in their first predetermined position. 8. Sensing device as specified in claim 7, characterized in that the light control device includes a perforated disc which is arranged between the light source and the light receiver, and which is drivably connected to the drive motor device connected to the respective organs which react to gravity and magnetism. 9. Sensing device as specified in claim 1, 3 or 8, characterized in that the drive motor device includes a first stepper motor which is arranged on the drill string and is drivably connected to the first wobble bracket, another stepper motor which is arranged on the first wobble hoop and is drivably connected to the second wobble hoop and the rotatable shaft, and a third stepping motor which is arranged on the first wobble hoop and is drivably connected to the third wobble hoop. 10. Sensing device as stated in one of claims 1-9, characterized in that the control device comprises activation means for operating each stepper motor to bring each of the means that reacts to gravity or magnetism to the first predetermined position, a first stop means that serves to receiving a position signal when each gravity or magnetism responsive member has reached its first predetermined position and to produce a stop signal to interrupt the operation of the associated actuating means, terminating means serving to receive first signals when each gravity responsive member or magnetism, is in its first predetermined position and to generate a first termination signal when all means responsive to gravity or magnetism are in their first predetermined positions, signal detecting means serving to receive signals from each of said means g to generate an output signal, org sense which responds to the output signal from the signal detection means and the occurrence of the termination signal, and which serves for reactivation. of the actuating means to actuate the positioning means to move each of the gravity or magnetism responsive members from its first position to the second position, other stop means to determine when each gravity or magnetism responsive member has reached its second position and to produce another stop signal to terminate the operation of the associated operating organs, and measuring organs for measuring the elapsed movement of each of the organs that react to gravity or magnetism, from its first position to its second position and to produce information in accordance with the measurements. 11. Sensing device as stated in claim 10, characterized in that the activation devices include pulse-generating devices for generating pulses that serve to drive the positioning devices, and that each of the first and second stop devices includes a gate that serves to interrupt the operation of the pulse- generative organ. 12. Sensor as stated in claim 10, characterized in that it further includes means for generating an initiation signal which serves to facilitate a first operating mode of the control device, means for generating first mode operating signals which serves to drive the control device in a first operating mode , and means responsive to simultaneous occurrence of the initiation signal and the operation signal for the first mode of operation, to initiate operation of the activation means. 13. Sensing device as stated in one of claims 10-12, characterized in that the first stop means comprise means which react to the simultaneous occurrence of the initiation signal and the positioning signal supplied to the first stop means, in order to terminate the operation of the activation means. 14. Sensing device as set forth in one of claims 10-13, characterized in that each of the devices that react to gravity or magnetism includes devices for producing an error signal in accordance with their deviation from a desired position, and that the signal detection devices include devices for sensing of the size of the error signal, and means for sensing the sign of the error signal. 15. Sensing device as set forth in one of claims 12-14, characterized in that it further comprises devices for generating operating signals for another mode, and that the signal detection devices include devices for generating a sign signal which serves to move each of the devices that react on gravity or magnetism, in the direction where the error signal is reduced, and means for producing a magnitude signal which serves to activate the activation means when the operating signals for another mode appear at the same time. 16. Sensing device as stated in claim 15, characterized in that it further comprises a first port which serves to receive the size signal and the operating signal for the second mode, the first port producing an input signal upon simultaneous occurrence of the size signal and the operating signals for the second mode which serves to operate the activation means, while the operation of the activation means ceases in the absence of one of the aforementioned signals. 17. Sensing device as stated in one of claims 14-16, characterized in that the stopping device includes devices which react to a predetermined number of changes in the sensing of the sign signals, in order to interrupt the operation of the activation devices when the operating signal for the second mode is removed from said gate. 18. Sensing device as stated in one of claims 14-16, characterized in that the second stop device comprises devices that respond to the absence of error signals from the devices that respond to gravity or magnetism during a predetermined time period, in order to terminate the operation of the activation devices upon removal of the operating signal for the second mode from said port. 19. Sensing device as specified in claim 10, characterized in that the termination devices receive a different signal when each device that reacts to gravity or magnetism is at its different position, and produces a different termination signal when all devices that react to gravity or magnetism are located themselves in their other positions. 20. Sensing device as set forth in claim 19, characterized in that it comprises devices that respond to the appearance of the second termination signal, for repetitively running through the control device to bring each of the devices that respond to gravity or magnetism to its first predetermined position and then to the other position. 21. Sensing device as specified in claim 10, characterized in that it further includes storage devices which serve to receive measurement information from the measurement devices and to store this information for later use. 22. Sensing device as specified in claims 20 and 21, characterized in that it comprises devices that react to the occurrence of the second termination signal, for the transmission of information from the measuring devices to the storage device. 23. Sensing organ as specified in claim 10, characterized in that the operating organs are a pulse generator and that the measuring organ is a counter for counting the net number of pulses emitted from each pulse generator, and which serves to drive each positioning organ. 24. Sensing device as specified in one of claims 10-14, characterized in that it further includes one integrator which serves to receive error signals from the associated devices which react to gravity or magnetism, the integrator being reset by the output signal from the activation device. 25. Sensor as specified in claim 24, characterized in that it further comprises summation means for summation of the output signal from the integrator and the error signal and supply of the summed signal to associated signal detection means. 26. Sensing device as stated in one of the preceding claims, characterized in that it comprises devices for generating pressure pulses in accordance with the measurement information in a mud stream in the drill string, the pressure pulses being transmitted via the mud stream to the surface. 27. A rotary sensor for sensing the absence or presence of the rotary movement of a rotatable part in an ambient magnetic field and for activating a control mechanism in the absence of the part's rotation, characterized in that the rotary sensor comprises a flux gate magnetometer for generating an output signal as a function of the angular relationship between the magnetometer and the direction of the surrounding magnetic field, ie the fluxgate magnetometer is arranged to be mounted in a drill string segment, means for generating and for transmitting an input signal to the fluxgate magnetometer, the magnetometer having a first output signal which is an even-numbered harmonic of said input signal, a first detector which serves to receive the first input signal, means for generating a reference signal with the same frequency as the first output signal, as the reference signal is supplied to the first detector, and as the detector compares the phase difference between the first output signal and the reference signal and produces another output signal with a frequency that is consistent with the rotational speed of the drill string, second detector means for receiving the second output signal and for producing a third output signal whenever the second output signal crosses a reference level, and signal producing means for receiving the third output signal and for producing a fourth output signal when the third output signal is in accordance with the absence of turning motion. 28. Organ as stated in claim 27, characterized in that the flux gate magnetometer is a ring core magnetometer. 29. Organ as stated in claim 27, characterized in that the first output signal is the second harmonic of the input signal. 30. Organ as stated in claim 27 or 29, characterized in that the reference is a signal which has a frequency equal to twice the frequency of the input signal to the magnetometer and has the same phase as this. 31. Organ as stated in claim 27, characterized in that the second detector is a zero crossing detector for producing pulse-shaped signals. 32. Organ as specified in one of claims 27-31, characterized in that the signal-producing organs comprise a counter for counting the pulses in the third output signal, the counter being reset at predetermined intervals, and logic organs connected in such a way that they receive the output signal from the counter for to produce the fourth output signal in dependence of the state of the counter in the predetermined time interval. 33. Rotation sensor as specified in one of claims 27-32, characterized in that it is designed to sense the absence of the rotation movement of a drill string in the earth's magnetic field. 34. Method for measuring directional parameters for a drill string with sensing means as stated in one of claims 1-9, characterized by the steps that one drive motor connected to the first wobble bracket is put into operation to lead the first means that react to gravity to a first predetermined position and then to another position having a predetermined setting with respect to the gravitational force, as determined by first setting signals, that when the first organs responsive to gravity are in their first predetermined position, a first is detected and produced home signal, that the movement of the first bodies to the first position ends on receipt of. the first home signal, that the first gravity-responsive organs are moved to the second position after the first predetermined position is reached, that the net movement of the first gravity-responsive organs is measured from the first predetermined position to the second position by the means for determining a first directional parameter of the drill string, that a second drive motor connected to the second rocker arm is actuated to drive the other means responsive to gravity to a first predetermined position and then to a second position having a predetermined setting with consideration of the gravitational force, as determined by the other setting signals, and that when the other organs that respond to gravity are in their first predetermined position, a first home signal is detected and produced, that the movement of the other organs that respond to gravity , until the first position ends on receipt of the first home sign al, that the other organs that respond to gravity are moved to their second position after the first predetermined position is reached, that the net movement of the other organs that respond to gravity is measured from the first predetermined position to the second position in order to determining another directional parameter of the drill string, that a drive motor connected to the third wobble bar is operated to move the means responsive to magnetism to a first predetermined position and then to a second position having a predetermined setting with respect to the earth's magnetic field as determined by third setting signals , that when the organs that respond to magnetism are in their first predetermined position, a first home signal is detected and produced, that the movement of the organs that respond to magnetism, the first position ends upon receiving the first home signal, that the organs that respond to magnetism is carried to its second position after the first the predetermined position is reached, and that net movement of the means responsive to magnetism from the first predetermined position to the second position is measured to determine a third directional parameter of the drill string. 35. Method for controlling the operation of sensing means for boreholes-drilling means having a plurality of movable sensors which serve to produce borehole parameter signals, and positioning means associated with each parameter sensor for posi- sioning of the parameter sensors for measuring parameters for a borehole, characterized by the following step that each positioning means is operated to position each parameter sensor in a first predetermined position, that a first stop signal is generated which serves to terminate the operation of each positioning means upon receipt of a positioning signal from the associated parameter sensor when the associated parameter sensor has reached its first predetermined position, that a first termination signal is produced when all the parameter sensors are in their first predetermined positions, that signals from each parameter sensor are detected and a output signal, that the positioning means are brought into operation again to move each parameter sensor from its first position to another position in response to the output signal from the associated parameter sensor when the termination signal is present, that it is determined when each parameter sensor has reached its second position and another stop signal is generated which serves to end the operation of the associated activation means, and that the movement of each parameter sensor from its first position to its second position is measured, while at the same time producing information consistent with the movements. 36. Method for sensing the absence of a drill string's rotating movement in the earth's magnetic field and for activating parameter sensing devices in the absence of the drill string's rotation, characterized in that the method includes the following step, that flux gate magnetometer devices are rotated in the earth's magnetic field to produce an output signal which a function of the angular relationship between the magnetometer element and the direction of the earth's magnetic field, that an input signal is supplied to the fluxgate magnetometer element, the fluxgate magnetometer element having a first output signal which is an even-numbered harmonic of the input signal, that a reference signal is produced with the same frequency as the first output signal, that the phase difference between the first output signal and reference signal is compared, while another output signal is produced with a frequency corresponding to the rotation speed of the drill string, so that a third output signal is produced every time the second output signal crosses a reference level and that a fourth output signal is provided when the third output signal is consistent with the absence of rotary motion.