GB1570758A - Binary code wheel digitiser - Google Patents

Description

(54) BINARY CODE WHEEL DIGIESER (71) We, LYNES, INC., a corporation organised and existing under the Laws of the State of Texas, United States of America, of 8787 Tallyho, Houston, Harris County, Texas 77017, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment :- This invention relates to binary code wheels and sensors for providing electric signals representing different digital values according to the relative angular positions of the wheel and sensors. The invention can be applied, for example, to measuring environmental conditions such as pressure, temperature, humidity, velocity, fluid displacements or movement, presence or absence of certain elements in the environment, and the like.

According to the present invention a binary code wheel comprises a body made of quartz having a metalized code pattern, the code pattern being arranged in a plurality of concentric bands with the outermost band having the least significant bit indication and the innermost band having the most significant bit indication, the concentric bands being divided into a plurality of regions of substantially transparent form indicative of one binary condition and a plurality of opaque regions indicative of the other binary condition, the code pattern being arranged in a multiphase configuration such that each bit is sensed along its own concentric band on a pre-assigned radius and is weighted with respect to its origin of pattern.

The different radii along which values are sensed may be regarded as different phases of the sensing system. In one advantageous form of two-phase digitiser, even number bits are sensed along a first radius and uneven number bits are sensed along a second radius.

One particularly advantageous field of application of the present invention is the measurement of down-hole pressure and temperature of an oil well.

There are a number of down-hole pressure and temperature measuring devices known in the art, each having certain advantages and disadvantages. Generally, the prior devices measure pressure by analogue techniques, such as current measurement, and accordingly, the accuracy of the measurement is dependent upon the length of the electrical wire from the measuring device down-hole to the remote indicator or recorder which monitors the measurement. This is so, since the length of the wire may vary from well to well due to depth of the hole and the distance of the indicator or recorder from the hole.

Also, the resistance of the electrical wire may vary due to temperature variations in the hole. Current leakage may also occur which further degrades the accuracy of the measurement. Another problem is that often small motors or the like are used with the measuring apparatus which increases the cost as well as the size of the apparatus.

Further, calibration accuracy of the known measuring devices is of prime concern due to the above-named variations which have to be compensated for.

A binary code wheel digitiser embodying the invention may be used in place of analogue elements to sense one of the conditions and, in view of its multi-phase construction, can reduce the size of the measuring apparatus while increasing its accuracy. Furthermore, by sampling the digitiser output at a frequency related to the other of the conditions to be measured there can be derived a pulse train which represents both pressure and temperature.

Because digital techniques are used, the accuracy of the measurement is not affected by the length of the wire from the hole to the recorder or indicator.

In order that the invention may be better understood, one form of pressure and temperature sensing apparatus including a digitiser embodying the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view in section of a pressure and temperature sensor in which a code wheel digitiser embodying the present invention is used; Figure 2 is a diagram of a code wheel embodying the invention; Figure 3 is a diagram illustrating another code wheel in combination with gating windows through which the code wheel is exposed to the sensors; Figure 4 is a schematic block diagram representation of a digital logic circuit for coding the sensed pressure and temperature conditions in the apparatus of Figure 1; and Figures 5A to 5P are diagrams illustrat ing waveforms present in the circuit of Figure 4.

Figure 1 illustrates pressure and temperature sensing apparatus which may be used in any number of environments for sensing the conditions thereof and in which a digitiser embodying the invention is used.

Specifically, the apparatus is directed to sensing the environmental conditions downhole in an oil well, and in this instance the sensing of the down-hole pressure and temperature. The environmental condition sensing apparatus 2 is comprised of a housing 4 which includes a Bourdon tube 6 which is secured at one end thereof in a Bourdon tube holder 8 which is secured to a Bourdon tube housing 10 by suitable fastening means (not shown). A filter 12 allows gas or the like to be sensed through an opening 14 for determining the pressure and temperature thereof. The Bourdon tube 6 is attached to a coupler 16 which has a coupling wire 18 attached thereto which in turn is attached to a code wheel shaft 20. The shaft 20 has a code wheel 22 attached thereto such that the code wheel rotates in accordance with the rotation of the Bourden tube 6, which rotation is indicative of the pressure of the gas sensed.

The code wheel shaft 20 turns in bearings 26 formed in a code wheel housing 24. A pair of arms 28 and 30 are attached to the Bourdon tube housing 10 by set screws 32 and 34. Attached to the arms 28 and 30 intermediate the Bourdon tube housing and the code wheel 22 is an emitter board 36 which has radiant energy transmitters 38 situated at spaced increments therein. The code wheel has a Gray code pattern plated thereon forming concentric bands, which code when read is indicative of the amount of rotation of the Bourdon tube 6, and therefore is indicative of the pressure sensed by the tube. The radiant energy transmitters 38 are each aligned with a given one of the concentric bands, such that the light from a given transmitter is passed or blocked by a given band dependent upon the code appearing directly above the given transmitter. This will be described in more detail shortly in relation to Figures 2 and 3. Attached to the arms 28 and 30 above the code wheel 22 is a sensor board 43 which has a number of radiant energy sensors 40 positioned therein each being in radial alignment with given ones of the transmitters 38. A gating window 44 is attached to the sensor board 42 by screws 46 and 48. The gating window has a number of apertures therein each of which is in radial alignment with given ones of transmitters and sensors, such that any light passed by the code wheel is passed through the respective apertures in the gating window to the sensors. Each aperture in the gating window has a width which is substantially equal to the width of a least significant bit (LSB) code indication on the code wheel.

A header 50 is sealably mounted in the top-most portion of the housing 4, and has passed therethrough a plurality of lines as indicated at 52, which lines for example may be representative of a power input line, as well as a digital information output line.

The power line is connected to a control board 54 as well as a logic board 56 with a connection 58 between the boards 54 and 56 being representative of control and power lines. The control board 54 has a number of elements such as 60 attached thereto which may take different forms dependent upon the power design chosen by a particular engineer. Likewise, the logic board 56 has a number of logic elements 62 attached thereto which may form the logic elements comprising the digital coding system. A plurality of conductors 64 are connected between the control board 54 and the sensor board 42, for applying power to the sensor board as well as to the emitter board. A plurality of conductors 66 are attached between the logic board 56 and the sensor board 42 for connecting the output of the sensors to the logic board such that the logic network may act upon the signals sensed to provide a digital output signal indicative of the pressure and temperature sensed down hole. The temperature sensing apparatus may be located anvwhere within the Bourdon tube housing 4 for sensing the temperature therein and is connected to the logic board for reasons to be explained shortly.

Refer now to Figure 2 which is a detailed diagram of the code wheel. The code wheel is made of quartz having optical quality.

One face of the code wheel is metallised according to the Gray code used. Regions of the wheel which are to represent a logic zero condition are made opaque by the metallising technique as indicated by the shaded areas, whereas the regions which are to be indicative of a logic one condition are left transparent as indicated by the unshaded areas. The code pattern is deposited by metallisation of the surface, in such a way that the sequential increase in coded numbers (for example Gray coded numbers) is in a counterclockwise direction.

The weight of the bits is in increasing numbers from 1 to 9, with the first or least significant bit (LSB) being situated on the outermost band 70, with the ninth bit being situated at the innermost band 72. The intermediate bands are clearly recognisable from the figure 7. The code wheel shown is for a two phase configuration, that is the even number bits are sensed along a given radius, whereas the uneven bits are sensed along a second radius for example 1800 removed from the one radius. This will be more clearly seen in relation to Figure 3. It is to be appreciated however that the invention may be practiced utilising any multiple-phase code wheel digitiser, i.e. any code wheel digitiser in which sensors are along a plurality of radii. For example if a three phase code wheel is utilised the sensors may be placed along three radii which are spaced 1200 apart. It is to be understood however that the degree of spacing is the designer's choice with the only constraint being that the sensors do not touch one another. For rotation of the wheel the zero starting point for the even numbered bits is indicated by the line 74 and the end region for the even numbered bits is indicated by the line 76. The zero starting point for the odd numbered bits is indicated by the line 78 and the end point for the odd numbered bits is indicated by the line 80. It is to be appreciated that any number of code wheels different than the one illustrated may be utilised in the practice of the present invention.

For example, code wheels may be utilised wherein less than 360" of the wheel is utilised, for example as little as 1200 of the wheel may be utilised and coded.

The code wheel in Figure 2 was for a nine bit system. Figure 3 illustrates a twophase code wheel 82 for a system in which only five bits are utilised. This gives a clearer representation of the positioning of a stationary gating window 84 in relation to the wheel. Apertures 86, 88 and 90 are situated in radial alignment with the odd bit concentric bands 1, 3 and 5 along a first radius 92. Windows 94 and 96 are positioned in tradial alignment with the concentric bands indicative of even numbered bits 2 and 4 along a second radius 98 which is displaced 1800 from the radius 92. The placement of alternate gating windows on different radii results in a smaller diameter of the code wheel since the respective concentric bands may be made smaller in diameter since the sensors operative with the respective gating windows need not be placed as close to one another as is the case if a one phase system is used, that is a system where consecutive gating windows are in radial alignment along a single radius. This is of primary concern when the code wheel is used in an environment where space is a primary consideration. It is well known that in apparatus for sensing downhole pressure and temperature and the like, that the apparatus must be small in size to effect the sensing operation. It follows therefore that the reduction in size of any element in the apparatin, such as the code wheel, is of prime importance.

Refer now to Figure 4 which is a schematic and block diagram representation of a digital logic circuit which is used to provide a digital output word indicative of the two environmental conditions sensed, namely the pressure and the temperature.

The symbols 5a! to 5p found on Figure 4 are indicative of the circuit points at which the waveshapes as illustrated by Figures SA to 5P respectively are manifested in the circuit of Figure 4. The waveshapes illustrate the operation of the circuit for one pressure sensed at two different temperatures. That is, the left-most portion of the diagrams illustrate the timing for the one pressure at a temperature T1, and the rightmost portion of the diagrams illustrate the timing for the one, i.e. the same, pressure at a temperature T2. The Bourdon tube 6 is connected to the code wheel by way of the wire 18 and the coupler 16 as was previously described. The radiant energy transmitters 38, which in practice may take the form of gallium arsenide light-emitting diodes, are illustrated in schematic form and are connected in series to a source of operating potential 100. The outputs of the respective diodes are illustrated schematically by way of resistors 102 in alignment with the respective code indicating con centric bands along the code wheel with the uppermost diode being aligned with the outermost or least significant bit band on the code wheel, with the lowermost or most significant bit band being aligned with the most significant bit concentric band on the code wheel. The metallized or masked regions are indicated by the shaded regions such as 104 in the diagram. It is seen therefore that the code wheel is positioned in a nine bit configuration indicative of a sensed pressure wherein the code is 101010010. The light sensors 40 are illus- trated in schematic form and may for example be light responsive transistors as indicated or photodiodes or the like, all of which are readily available as off the shelf items. The collectors of the transistors forming the respective light sensors are connected in parallel to a source of operating potential 106. Each of the emitter electrodes of the respective transistors are connected in parallel to circuit ground by way of resistors 108. It is seen that when a given light sensor senses light, the transistors become conductive and an output signal is developed across its associated resistor which is indicative of a binary one signal condition, that is the sensing of light. Conversely, if light is not sensed a signal is not developed which is indicative of a binary zero condition. The respective outputs of the light sensors are connected to respective first inputs of AND gates 110-126.

These respective gates are sampled at successive time intervals to determine the sensing conditions of their associated light sensors 40. The description of the control or timing network for controlling the sampling of these gates follows.

A temperature sensing device 128 is housed in the Bourdon tube housing for sensing the temperature therein and is connected to a temperature responsive oscillator 130 which provides timing signals or pulses at its output which have a duration or width which is determined by the temperature sensed. Stated in another way, the temperature sensed controls the frequency of the signal provided at the output of the oscillator 130. It follows that for a temperature T1 the output of the oscillator is at a first frequency F1 and for a different temperature T2 the output of the oscillator is at a second frequency F2. The signal output from the oscillator 130 is provided to the input of a waveshaper and divideby-N counter 132 which provides a pulse train of a squarewave nature at its output, with the duration of the respective pulses and the frequency thereof being determined by the frequency output of the oscillator 130. This pulse train (Fig. 5A) is provided as a signal input to a program counter 134, an AM) gate 136, and a first input 138 of a sampling pulse generator 140. The program counter is well known in the art and may take any one of many different physical forms. In any event it counts the input pulses from the counter 132. Connected to respective output terminals of the program counter 134 is an AND gate 142 which is connected to provide an output enable pulse for a predetermined time interval, that is a predetermined count time of the program counter. The signal output from the gate 142 (Fig. SB) is applied to inputs of the gate 136 and an inverting device 144, with the output of the device 144, being connected to the second input 146 of the sampling pulse generator 140.

The output from the AND gate 136 (Fig.

SL) is the pulse output from the counter 132 during the enable time interval as determined by the signal output from the gate 142. The output from the gate 136 is connected to second inputs of the gates 110 to 126 for providing a gating signal such that the output from the respective gates provide a signal output having a duration equal to the duration of a pulse from the counter 132 whenever the gates 110 to 126 are enabled as determined by the respective inputs from the sampling pulse generator 140 and the sensors 40. The sampling pulse generator 140 may take many different logic forms and for example may take the form of a counter and associated gates. In relation to Figures SC- 5K it is seen that the gates 110 to 126 are successively enabled for sensing the binary condition of the respective radiant energy sensors which are connected thereto for sensing the down-hole pressure. The sampling pulse at bit time 9 (Fig. 5K) which is applied to the input of gate 126 is also applied to the input of an OR gate 148 in a reset circuit 150 for providing a reset signal on a line 152 for resetting the program counter 134 and the sampling pulse generator 140 for initiating each consecutive cycle of operation.

The respective outputs of the gates 110 to 126 are connected to respective inputs of an OR gate 154. In accordance with known operation of an OR gate the signal appearing at the output thereof (Fig. 5M) is representative of the successively sensed binary conditions of the respective gates 110 to 126. The pulse output indications from the gate 154 as illustrated by Figure SM are indicative of sensed binary one conditions, and it follows that the intervals in the binary word where there is no pulse the binary word where there is no pulse is indicative of a binary zero condition. The output of the OR gate 154 is connected to the base electrode of an NPN transistor 156 and to the input of an inverter 158. The output signal from the inverter 158 is a train of pulses which are indicative of the time intervals at which a binary zero indication is sensed, and these signals are connected to an input of an AND gate 160 which has a second input connected to the ouput of the AND gate 136. It follows therefore that the signal appearing at the output of the AND gate 160 (Fig. SN) is a series of pulses, which pulses are indicative of the time interval at which binary zero indications are sensed as controlled by the timing of the gate 136.

The output of the AND gate 160 is connected to the base electrode of an NPN transistor 162. The emitter electrodes of the transistors 156 and 162 are connected to circuit ground, and the collector electrodes thereof are connected to an output terminal 164 by way of resistors 166 and 168 respectively. The latter resistors are also connected to a source of regulated voltage 170 which controls the reference output current appearing at the terminal 164. The resistor 166 is chosen to have an impedance which is larger than the impedance of the resistor 168 such that it may be readily seen when a given one of the transistors is conducting. In an interval of time when neither of the transistors is conductive the output current appearing at the terminal 164 is at a predetermined reference level as indicated at 172. When the transistor 156 becomes conductive which is indicative of a binary one condition for a given interval of time a given amount of current flows through the resistor 166 and a current pulse of a first amplitude indicative of a binary one indication is manifested at the terminal 164 as indicated by the pulse 174. When the transistor 162 is conductive which is indicative of a binary zero condition a greater amount of current is drawn since the resistor 168 is smaller than the resistor 166 and a current pulse as indicated at 176 is manifested at the output terminal 164. It follows that the sequence of bits is indicative of the pressure sensed whereas the duration or width of the bits, that is the frequency of the message is indicative of the temperature sensed.

The effect of the temperature sensed on the output word is more readily seen in relation to Figures 5A to SP. Figure SA illustrates the output from the counter 132 at temperatures T1 and T22, and it is seen that the duration of the pulses is less at temperature T1 than the duration of the pulses at temperature T2. Stated another way, it is seen that the frequency of the pulses at temperature T2 are higher than the frequency of the pulses at temperature T2. Since the operation of the remaining counters and gate in the logic network are controlled by the output of the counter 132 it is readily apparent from the remaining waveshapes illustrated that the duration or frequency of the output word changes while the bit sequence remains the same for a given sensed pressure as indicated by Figure 5P which is a return-to-base current waveform.

WHAT WE CLAIM IS:- 1. A binary code wheel comprising: a body made of quartz having a metalized code pattern, the code pattern being arranged in a plurality of concentric bands with the outermost band having the least significant bit indication and the innermost band having the most significant bit indication, the concentric bands being divided into a plurality of regions of substantially transparent form indicative of one binary condition and a plurality of opaque regions indicative of the other binary condition, the code pattern being arranged in a multiphase configuration such that each bit is sensed along its own concentric band on a pre-assigned radius and is weighted with respect to its origin of pattern.

2. A binary code wheel according to claim 1 comprising a two-phase configuration, even number bits being sensed along their respective bands and weighted with respect to their origin of pattern on a given radius, and odd number bits being sensed along their bands and weighted with respect to a second origin set on a second radius.

3. A binary code wheel as defined in claim 1 or 2, wherein the code pattern on the code wheel is a Gray code pattern.

4. A binary code wheel, substantially as here in described with reference to figure 2 or Fig. 3 of the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   The output of the AND gate 160 is connected to the base electrode of an NPN transistor 162. The emitter electrodes of the transistors 156 and 162 are connected to circuit ground, and the collector electrodes thereof are connected to an output terminal 164 by way of resistors 166 and 168 respectively. The latter resistors are also connected to a source of regulated voltage

   170 which controls the reference output current appearing at the terminal 164. The resistor 166 is chosen to have an impedance which is larger than the impedance of the resistor 168 such that it may be readily seen when a given one of the transistors is conducting. In an interval of time when neither of the transistors is conductive the output current appearing at the terminal 164 is at a predetermined reference level as indicated at 172. When the transistor 156 becomes conductive which is indicative of a binary one condition for a given interval of time a given amount of current flows through the resistor 166 and a current pulse of a first amplitude indicative of a binary one indication is manifested at the terminal 164 as indicated by the pulse 174. When the transistor 162 is conductive which is indicative of a binary zero condition a greater amount of current is drawn since the resistor 168 is smaller than the resistor 166 and a current pulse as indicated at 176 is manifested at the output terminal 164. It follows that the sequence of bits is indicative of the pressure sensed whereas the duration or width of the bits, that is the frequency of the message is indicative of the temperature sensed.

   The effect of the temperature sensed on the output word is more readily seen in relation to Figures 5A to SP. Figure SA illustrates the output from the counter 132 at temperatures T1 and T22, and it is seen that the duration of the pulses is less at temperature T1 than the duration of the pulses at temperature T2. Stated another way, it is seen that the frequency of the pulses at temperature T2 are higher than the frequency of the pulses at temperature T2. Since the operation of the remaining counters and gate in the logic network are controlled by the output of the counter 132 it is readily apparent from the remaining waveshapes illustrated that the duration or frequency of the output word changes while the bit sequence remains the same for a given sensed pressure as indicated by Figure 5P which is a return-to-base current waveform.

   WHAT WE CLAIM IS:- 1. A binary code wheel comprising: a body made of quartz having a metalized code pattern, the code pattern being arranged in a plurality of concentric bands with the outermost band having the least significant bit indication and the innermost band having the most significant bit indication, the concentric bands being divided into a plurality of regions of substantially transparent form indicative of one binary condition and a plurality of opaque regions indicative of the other binary condition, the code pattern being arranged in a multiphase configuration such that each bit is sensed along its own concentric band on a pre-assigned radius and is weighted with respect to its origin of pattern.
2. 2. A binary code wheel according to claim 1 comprising a two-phase configuration, even number bits being sensed along their respective bands and weighted with respect to their origin of pattern on a given radius, and odd number bits being sensed along their bands and weighted with respect to a second origin set on a second radius.
3. 3. A binary code wheel as defined in claim 1 or 2, wherein the code pattern on the code wheel is a Gray code pattern.
4. 4. A binary code wheel, substantially as here in described with reference to figure 2 or Fig. 3 of the accompanying drawing.