CH641277A5 - METHOD AND DEVICE FOR MEASURING FLOW IN A PIPE BY DETERMINING THE CORIOLIS FORCES. - Google Patents

Description

The present invention relates to a method for measuring the flow rate by measuring the Coriolis forces which are generated by the flow of material through a moving tube, and to an apparatus for carrying out the method.

Heretofore, flow meters of the type to which the present invention relates have been known as gyroscopic flow meters or Coriolis flow meters. In essence, both types of flow meters relate to the same principle. In simple terms, the Coriolis forces are based on the radial movement of masses from a first point to a rotating body to a second point. From this movement it follows that the peripheral speed of the mass changes, i.e. the mass is accelerated. The acceleration of the mass creates a force that is in the plane of rotation and perpendicular to the momentary radial movement. Such forces are responsible for the pressure in gyroscopes. Known devices for measuring the mass flow on this

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Ways include pressure sensitive strain compensators or other such mechanically pivotable devices.

Various solutions have been proposed that use the Coriolis forces to measure mass flow. So e.g. U.S. Patent Nos. 2865201 and 3312512 disclose gyroscopic flow meters that have a complete loop that is continuously rotated or swung.

Other flow meters use essentially the same forces, but prevent flow reversal by using a loop less than 180 °, as described in U.S. Patent No. 3,485,098. In both cases, the devices are so-called alternating types, i.e. the tube is vibrated about an axis and the fluid flowing through the tube first flows away from the center of rotation and then towards the center of rotation and thus generates Coriolis forces as a function of the flow velocity of the fluid through the loop.

However, since there is a means for generating the Coriolis forces, all known devices generate the same forces, but have different specific devices for measuring such forces. Although the concept is simple and straightforward, practical results in accurate flow measurement have not been achieved.

With the Roth flow meter e.g. Transducer or a gyroscopic coupling used as a display device. Roth describes the gyroscopic coupling as very complicated and the transducers are described as very flexible tubes, such as bellows. The latter Roth patent is primarily aimed at the arrangement of such flexible bellows.

Another classic solution for measuring the force proportional to mass flow relies firstly on driving or vibrating a pipe by means of a rotary movement about an axis and then on measuring the additional energy required to carry such a pipe through which a fluid flows will drive. The Coriolis forces are very small compared to the driving forces, and as a result, it is very difficult to accurately measure such small forces in connection with the large driving force.

Another measuring device is described in column 7, lines 1-23 of US Patent No. 3485098. In this device, speed sensors independent of the drive device are arranged in order to measure the speed of the movement of the pipe, which is caused by the deformation of the pipe caused by the Coriolis forces. While worthwhile information can be obtained through such measurements, the speed sensors require a measurement of a time-limited speed which is superimposed on the very large pipe vibration speeds. The gyroscopic forces must therefore be determined together with the speed measurements under limited and special conditions, as described below. The mathematical analysis confirms that the speed measurements give the best edge results.

The aim of the invention is to provide a method for measuring the flow rate of the type mentioned at the outset, with which a very precise measurement is possible with a simple and inexpensive design.

This object is achieved according to the invention with the characterizing features of claim 1.

An apparatus for performing the method is characterized according to the invention by the features of claim 2.

The attachment of the U-tube at its free leg ends to the holder, so that the other end protrudes from the holder, is advantageous because, in the case where the deformation is measured, such an attachment essentially involves the deformation resulting from the Coriolis forces is completely outside the elastic deformation in the tube and is free of mechanical swivels apart from the bending of the tube.

In order not to jeopardize the accuracy of the flow meter by measuring one of the opposing forces, the apparatus and method of the present invention is so specifically designed that the forces caused by the two unmeasured opposing forces, i.e. when speed resistance and mass acceleration are generated, are reduced. This is particularly successful where such forces accumulate, namely less than 0.2% of the torsional spring force. The attachment of the tube means that bellows and other such devices, which counteract the differences in pressure between the tube and the ambient pressure, are no longer required. The swiveling is carried out free of pressure-responsive separate swiveling devices.

Exemplary embodiments of the subject matter of the invention are explained in more detail below with reference to the accompanying drawings. Show it:

1 is a perspective view of an embodiment of a fluid flow meter according to the invention, FIG. 2 is a side view of the flow meter according to FIG. 1, which shows the oscillation at the center when there is no flow,

3 shows a side view of the flow meter according to FIG. 1, which shows the oscillation at the center in the upward direction during the flow,

4 shows a side view of the flow meter according to FIG. 1, which shows the oscillation at the center in the downward direction during the flow,

5 is a block diagram of the control circuit of the flow meter of FIG. 1;

6 is a block diagram of the display circuit of the flow meter of FIG. 1;

7 is a diagram of the display signals of the flow meter of FIG. 1 when there is no flow.

8 is a diagram of the display signals of the flow meter of FIG. 1 when there is flow through the pipe;

9 is a perspective view of another embodiment of the flow meter according to the invention, FIG. 10 is a circuit diagram of the control circuit and the display circuit of the flow meter of FIG. 9 except for the circuit for the deformation sensing,

11 is a circuit diagram of an embodiment of the deformation sensing arrangement which is suitable for generating the signal denoted by B in FIG. 10,

FIG. 12 is another circuit diagram for a purpose identical to that of FIG. 11;

Fig. 13 is another circuit diagram for a purpose similar to that of Fig. 11, and

14 is a circuit diagram of the synchronous demodulator of FIGS. 10, 12 and 13.

In all figures, the same elements are designated with the same reference numbers. Fig. 1 shows a flow meter 10, - which has a fixed holder 12 with a U-shaped tube 14 which is freely suspended on the holder. The U-tube is advantageously made of a tube-like material with an elasticity that is normally found in such materials as beryllium, copper, annealed aluminum, steel, plastic, etc.

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Although U-tube 14 is described as U-shaped, it may have legs that converge, diverge, or bevel. A continuous curve is possible. The U-tube 14 contains an inlet 15 and an outlet 16, which are connected to one another via an inlet leg 18, a web leg 19 and an outlet leg 20. The inlet leg 18 and the outlet leg 20 are parallel to one another, and the web leg 19 is arranged perpendicular to both. As mentioned above, significant deviations from the ideal design, e.g. 5 ° convergence or divergence does not result. Effective results can be obtained with rough deviations in the size of 30 or 40 °. However, since only little can be achieved in the embodiment in question, it is advantageous to arrange the two legs 18, 20 essentially parallel to one another. The tube 14 may be in the form of a partial arc, if appropriate.

However, the physical design of the U-tube 14 is not critical, although the vibration properties are important. In the exemplary embodiment of FIG. 1, which allows the deformation, it is crucial that the resonance frequency around the W-W axis is different from that around the 0-0 axis and that the resonance frequency around the W-W axis is the smallest resonance frequency.

A spring lever 22 is fastened to the legs 18 and 20 and carries a drive coil 24 and a sensor coil 23 at the end which lies next to the web leg 19. A magnet 25, which is seated in the drive coil 24 and the sensor coil 23, is held by the web leg 19. A control circuit 27, which is explained in more detail below, generates an increased force as a function of the sensor coil in order to set the U-tube 14 in oscillation at its natural frequency around the axis W-W. Although the U-tube 14 is freely suspended on the holder 12, an oscillation at the resonance frequency results in an amplitude in the bending oscillation about the axis W-W. The U-tube 14 essentially pivots about the axis W-W at the inlet 15 and at the outlet 16.

A first sensor 43 and a second sensor 44 are arranged at the intersection of web leg 19 and inlet leg 18 or outlet leg 20. The sensors 43 and 44, which are advantageously optical sensors, are actuated when the U-tube 14 passes through a nominal reference plane which is approximately at the center of the vibration. A display circuit 33, described below, is provided to display the flow measurements as a function of the time differential of the signal generated by sensors 44, 43. The function of the flow meter is better understood when looking at FIGS. 2, 3 and 4, which in simplified form illustrate the basic principle of the present invention. If the tube 14 is set in vibration without a fluid flowing through it, the inlet piece 18 and the outlet piece 20 are bent around the axis W-W, namely in the form of a pure bend, i.e. without torsion. As a result, as shown in FIG. 2, the web leg 19 maintains a constant angular position about the axis 0-0 over the complete oscillation. However, if the flow begins, the fluid flowing radially from the axis WW through the inlet piece 18 generates a first Coriolis force that is perpendicular to the direction of flow and perpendicular to the axis WW, while the flow in the outlet piece 20 generates a second Coriolis shaft that is again perpendicular to the radial flow direction, but opposite to the first Coriolis force, because the flow is directed in the opposite direction. If, as shown in FIG. 3, the web leg 19 runs through the center of the vibration, Coriolis forces generated in the inlet piece 18 and outlet piece 20 superimpose a pair of forces on the U-tube. As a result, the web leg 19 rotates angularly about the axis 0-0. This deformation is both a bending deformation and a torsional deformation essentially in the inlet piece 18 and outlet piece 20. The consequence of the frequency selection and the design of the U-tube 14 is that essentially the entire restrictive force on the Coriolis force pair is essentially an elastic spring deformation, is. This avoids the measurement of the force causing the speed inhibition and the opposite inertial force. At an essentially constant frequency and amplitude, the measurement of the angular deformation of the web leg 19 about the axis 0-0 at the nominal center of the vibration gives an accurate indication of the mass flow. This results in a significant improvement over the prior art. The determination of the web leg deformation with respect to the nominal undeformed center plane around the axis 0-0 in values of the time difference between the time of the leading leg, i.e. of the inlet leg 18 in the case of Fig. 3 passes through the center plane and the trailing leg, i.e. the outlet leg 20 in the case of FIG. 3, which passes through this plane, avoids the maintenance of constant amplitude and frequency, since changes in the amplitude are accompanied by compensating changes in the speed of the web leg 19. Only by driving the U-tube 14 at its natural frequency can the time measurements be carried out without taking into account the simultaneous amplitude regulation, as will be described in detail later. However, if the measurements are in one direction, i.e. 3, it will be necessary to maintain a precise angular alignment of the web leg 19 with respect to the nominal center plane. The requirement can even be avoided by subtracting the time measurements in the outward direction (FIG. 3) and the downward direction (FIG. 4). As those skilled in the art can easily determine, the movement in the downward direction (FIG. 4) causes the reversal in the direction of the Coriolis force pair and consequently, as shown in FIG. 4, the reversal in the deformation direction due to the Coriolis force pair.

A U-tube with certain frequency properties, which are based only on the mechanical design, is only vibrated around the W-W axis. A flow through the U-tube 14 causes a resilient deformation in the U-tube 14, which results from the angular movement of the web leg 19 about the axis 0-0 initially in a first direction during a phase of the oscillation and then in the opposite direction during the other oscillation phase results. Although the flow measurements by direct deformation measurement, i.e.

by scanning exposure of the web leg at the center of vibration with e.g. an analog scale, which is attached next to the end sections, and a pointer, which is held by the web leg 19, a preferred measuring method is based on the determination of the time difference between the moment when the leading and the trailing edge of the web leg 19 die Passes through the midpoint plane. This eliminates the need to control the amplitude. Furthermore, irregularities resulting from the poor alignment of the U-tube 14 with respect to the center point plane are eliminated from the measurement results by measuring the deformations caused by the upward vibration and the downward vibration.

. As shown in FIG. 5, the control circuit 27 forms a simple device for scanning the Si5 generated by the movement of the magnet 25 in the sensor coil 23

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gnals. A detector 39 compares the voltage generated by the sensor coil 23 with a reference voltage 37.

It follows from this that the gain of the drive coil amplifier 41 is a function of the speed of the magnet 25 in the sensor coil 23. The amplitude of the vibration of the U-tube 14 is thus easy to control. Since the U-tube 14 and the spring lever 22 oscillate at their resonance frequencies, frequency control is not necessary.

Additional information is also available from the circuit of FIG. 5. The output signal of the drive coil amplifier 41 is a sinusoidal signal at the resonance frequency of the U-tube 14. That resonance frequency is determined by the spring constant and the mass of the vibration system and that the spring constant is fixed and the mass changes only when the density of the flowing fluid changes, it can be seen that any change in the frequency is a function of the change in density of the the pipe is flowing fluid. Thus, since the period of the oscillation can be determined, it is a simple matter to count the frequency of a fixed oscillator during a period to determine a density factor. The density factor can e.g. converted to the fluid density by a record in which the time period is not a linear density function but only a determinable function thereof. If a direct display is desired, a microprocessor can be easily programmed to convert the density factor directly into the fluid density.

The operation of the display circuit will now be described with reference to the circuit shown in FIG. 6 and the associated diagram of FIGS. 7 and 8. The display circuit 33 is connected to the sensors 43 and 44. The sensors 43 and 44 generate signals when marks 45 and 46, which are attached to the web leg 19, pass the corresponding sensor in the center plane A-A. Sensor 43 is connected to inverter 48 via inverter 47, while sensor 44 is connected to inverter 50 via inverter 49. Due to the double inversion, there is a positive signal on line 52 which is fed to the set terminal of a flip-flop 54. There is also a positive signal on line 56 which is fed to the reset terminal of flip-flop 54. The flip-flop 54 is accordingly set due to the output of a positive signal from the sensor 44 and reset due to the subsequent output of a positive signal from the sensor 43. The inverted signal from the inverter 47 is fed to the set terminal of a flip-flop 60 via a line 48, while the output signal from the inverter 49 is fed to the reset terminal of a flip-flop 60 via a line 62. Thus, the flip-flop 60 is set due to the output of a negative signal from the sensor 43 and reset due to the subsequent output of a negative signal from the sensor 44. The output of the flip-flop 54 is connected to an AND gate 64 via a line 63. The AND gates 64 and 66 are both connected to the output of an oscillator 67. Accordingly, because of the output signal from flip-flop 54, the signal from oscillator 67 is output through AND gate 64 to line 68 and thus reaches the down-counting side of an up / down counter 70. Because of the output of a signal from the flip -Flop 60, the output signal from the oscillator 67 is output via the AND gate 66 to the line 69, which is connected to the ascending side of the up / down counter 70. In operation, the display circuit 33 thus outputs a counting signal with the oscillator frequency to the up / down counter 70, for the period during which the sensor 44 before the sensor 43 is actuated

is actuated during the downward movement of the U-tube 14. An up-counting signal is supplied to the up / down counter 70 during the period in which the sensor 43 is operated before the sensor 44 is actuated during the upward movement of the O-tube 14.

FIG. 7 shows waveforms which show the state in which the U-tube 14 vibrates without flowing through it, but in which the marks 44 and 46 are not exactly aligned with the plane A-A. Thus, as shown in the diagram, the sensors 44 initially switch earlier with respect to the ideal time represented by the vertical lines on the upstroke and switch later on the downstroke due to bad alignment of the mark 46. On the other hand, the sensor 43 switches and switches later in the upstroke earlier in the downstroke. However, if the output signals from flip-flops 54 and 56 are examined and further taken into account, then these flip-flops output either counting or up-counting signals to the up / down counter 70, it can be seen that this is the case when spreading out of FIGS Sensors 43 and 44 in operation flip-flop 54 produces an output signal during the upward stroke, while in view of the unchanged alignment of the marks 45,46, the flip-flop 60 generates a similar output signal during the downward stroke. Accordingly, over a complete cycle, the up / down counter is first counted down by a finite number by the output signal from flip-flop 54 via gate 64 and then counted up by an equal amount by the output signal from the flip-flop via gate 66. The resulting count in the up / down counter 70 is therefore zero, which represents the fact that there is influence.

On the other hand, when flowing, as shown in Fig. 8, the sensor 43 is actuated earlier than in Fig. 7, due to the deformation of the web leg 19 by the Coriolis force pair resulting from the fluid flow, as described above. The sensor 44 is operated later for the same reason. Thus, during the upward stroke, the flip-flop 54 is actuated for a substantially longer time than in the state shown in FIG. 7, since the misalignment of the marks 45 and 46 for the deformation of the web leg 19 is caused by the pair of Coriolis forces in the upward movement , is added. On the other hand, because of the downward movement, i.e. the generation of the smear of the signal from the sensors 43 and 44, the Coriolis force pair reversed and thus causes the sensor 43 to be switched off earlier and the sensor 44 to be switched off later. The flip-flop 60 is thus actuated for a reduced period of time. It can be seen from the relative actuation times of the two flip-flops that the count-down period from the up / down counter 70 is considerably longer than the count-up period that results from the actuation of the flip-flop 60. The resulting increased count on the counting side of the up / down counter 70 is an accurate indication of the flow over an oscillation period. The count in the up / down counter 70 after a given number of vibrations is directly proportional to the flow in the U-tube 14 during this period. The number of oscillations can e.g. can be determined by counting the number of operations of the flip-flop 54 on the counter 71, which is connected by line 72 to the output of the flip-flop 54. Thus, because of the appearance of “N” output signals from the flip-flop 54, the counter 71 is actuated and the sequencer 74 is then actuated. The sequencer 74 is connected to the oscillator 67 and, with the frequency from the oscillator 67, firstly blocks a blocking decoder 77 via the line 78 and then resets the up counter 70 via the line 75. The display 80 thus shows the accumulated count until the sequencer 74 is actuated again after an “N” output from the flip-flop 54

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from the up / down counter 70 at the polling time, and hence it indicates the flow rate for the period of "N" vibrations.

The total flow for a selected reset period results from the fact that the output from the up-down counter is fed to a digital counter 82, which is also connected to a quartz oscillator 84. Thus, the counts from the up / down counter 70 are integrated in terms of time. I.e. the fixed stable frequency from oscillator 84 and the integral applied to decoder 85 which is then connected to the display to measure the total flow during the period from the last actuation of reset 88, e.g. a switch connected to the digital counter to indicate.

As described above, the density factor can also be determined independently of the flow measurement by actuating the flip-flop 90 with a clock frequency of the output from the flip-flop 54 via the line 92. The output signal of the flip-flop 90 is fed to an AND gate 94 which, when actuated by the flip-flop 90, outputs the count from the quartz oscillator 84 to a counter blocking circuit 96. With the available time information in values of the counter readings from the quartz oscillator 84 and with the indication of the oscillation period from the flip-flop 90, the counter reading in the counter blocking circuit is thus a function of the density of the fluid in the U-tube 14, and thus the display is on the display device 98 the density factor described above. Since the density factor is not a linear function of the period of oscillation of the U-tube 14, the display on the display device 98 must be processed further, either manually by a diagram or by a microprocessor.

In summary, it is noted that with the flow meter 10 described, if desired, the instantaneous flow rate, the flow rate accumulated over a given period, the density relative to the fluid, and the flow rate, e.g. by dividing the flow rate by the density. According to tests, this is achieved with an accuracy of 0.1 or 0.2% and measures e.g. the gas flow at very low flow rates with very good accuracy. It is not necessary to regulate the amplitude of the frequency of the flow meter 10, e.g. measures the time between the output of one sensor to the output of the other sensor.

Another embodiment of the subject matter of the invention is shown in FIG. The flow meter 100 contains a holder 102 and a U-shaped tube 104 which is fastened in a fixed and freely pivotable manner. The U-shaped tube 104 has an inlet 105 and an outlet 106, which are connected to the inlet leg 108 and outlet leg 109. The legs 108 and 109 are arranged so that they can be pivoted at points 112 and 114 along an axis W'-W 'in order to oscillate the U-shaped tube 104 about the axis W'-W'. This can be facilitated by thinning the wall of the U-shaped tube 104 at the pivot points 112 and 114. However, such pivot points are continuous areas of the U-shaped tube 104 and can be unchanged tubes. The legs 108 and 109 are connected by a web leg 116, so that a complete U-shaped tube 104 is formed.

In contrast to the flow meter 10 in FIG. 1, the U-shaped tube 104 can advantageously have a lower bending resistance around the Coriolis force deformation axis and then around the vibration axis W'-W ', since the Coriolis force deformation is brought to zero. At web 116 are

Holders 119 are attached which hold magnets 118 which cooperate with a drive coil 120 to vibrate the U-shaped tube 104. Advantageously, the drive coil 120 is arranged on a self-supporting leaf spring 122 which is pivotally attached next to the axis W'-W 'and has a natural frequency which is essentially the same as that of the U-shaped tube 104 with the fluid in question . Of course, the attachment of the magnet and the drive coil can be interchanged, e.g. between pipe 104 and leaf spring 122. The leaf spring 122 can also be completely omitted if the holder 102 is a considerable mass compared to the mass of the pipe 104 and the fluid flowing through it. In most cases, however, it is preferred to oscillate the U-shaped tube 104 and the leaf spring with a common frequency phase out of phase by 180 ° in order to balance the forces within the flow meter 100 and to avoid vibration of the base plate.

The web 116 carries magnets 125 and 126 which extend downwards. The magnet 125 is arranged within a sensor coil 128, which is attached to the holder, while the magnet 126 is arranged within a sensor coil 129, which is also mounted on the holder 102. The magnet 125 projects into a drive coil 121, which is arranged symmetrically to the sensor coil -128, while the magnet 126 projects into a drive coil 132, which is also arranged symmetrically to the sensor coil 129. Deflection scanning devices 133 and 134, which are shown in a simple form in FIG. 9, but are shown in detail in FIGS. 11 to 13, are arranged next to the intersections of the legs 108 and 109 and the web 116.

The sensor coils 128 and 129 are connected in series in such a way that the movement of the magnets 125 and 126 into the sensor coils 128 and 129 generates a sinusoidal signal A with an amplitude that is proportional to the speed of the U-shaped tube 104 . This signal, the value of which is proportional to the speed of the magnets 125 and 126 and consequently a function of the oscillation amplitude of the U-shaped tube 104, is fed to an AC voltage amplifier 135 and a diode 136 which passes only the positive part of the sinusoidal signal to charge a capacitor 137. As a result, the input signal from diode 136 and capacitor 137 to a differential amplifier 138 is determined by the value of the sinusoidal signal. The differential amplifier 138 compares this input signal with a reference voltage VRi. If the capacitor voltage exceeds the reference voltage VRi, the amplifier 138 outputs a stronger signal. The output signal from AC amplifier 135, which is of course a sinusoidal signal in phase with the oscillation of U-shaped tube 104 and has a value determined by amplifier control through differential amplifier 138, carries coil 120 to the desired one Maintain vibration on the U-shaped tube 104. The signal A is also applied to a bridge, which is formed from resistors 140, 141 and 142 and a photo resistor 143. Resistor 144 is connected in a feedback loop between resistors 140 and 142. Resistors 140, 142 and 144 are e.g. connected to the positive input of differential amplifier 145. A variable light source 147, such as an LED 147, is connected to an output of a servo amplifier 150 via a resistor 148. A servo comparator 152 is a well known tool in servo systems, such as that found in Feedback Control Systems, Analysis and Synthesis, by D'Azo and Hopuis, ver5

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publicly described by McGraw Hill, 1966. This servo comparator 152 forms the feedback loop between an input of the servo amplifier 150 and an output of the servo amplifier 150. A signal B, which is a DC voltage signal that is proportional to the small unbalanced deformation of the U-shaped tube 104 and as follows with reference to FIG 11, 12 and 13 is generated, is applied via a resistor 153 to an input of the servo amplifier. The output signal of the servo amplifier 150 is compared with a reference voltage VR2 and fed to the LED 147 via the resistor 148. The light intensity of the LED 147 is controlled by the value of the signal B. The resistance value of the photoresistor 143 decreases with increasing light intensity of the LED 147 and as a result the signal present at the positive input of the differential amplifier 145 is reduced with respect to that signal present via the resistors 140 and 142 at the negative input of the differential amplifier 145. The output of differential amplifier 145 is thus 180 ° out of phase with signal A because the signal at the positive input is decreased while the signal at the negative input retains its value. In summary, the signal is reduced, the LED 147 goes dark and the photoresistor increases its resistance. This causes the output of differential amplifier 145, which is in phase with signal A, to be increased. The output of the differential amplifier 145 is connected to the drive coils 131 and 132 which, as described above, are mounted on the holder 102 and are connected in series and out of phase. The current through the drive coils 131 and 132 generates torque by attracting the magnet 125 and repelling the magnet 126, both of which are attached to the land 116. This torque across the web 116 compensates for the deformation of the web 116 which results from the Coriolis forces generated by the flow through the U-shaped tube 104.

The resistors 155, 156 or 157 can be connected to the drive coils 131 and 132 by means of a switch 159. These form a selectable load in order to set the scale factor and to apply a larger and smaller torque to the web 116. The output signal from the drive coils 131 and 132 connected in series is applied as an input signal to an input of a synchronous demodulator 162, which will be described in detail with reference to FIG. 14. The output signal of the synchronous demodulator 162 is a DC voltage signal which is proportional to the flow rate and consequently forms a measure of the flow rate. A DC voltmeter (not shown) can be connected to the output of the synchronous demodulator 162 to provide a visual reading of the flow rate through the U-shaped tube 104. The DC signal can also be used directly in a control loop with other system elements.

As shown in Fig. 11, the deflection sensors 133 and 134 can e.g. have a left mark 164 and a right mark 165 protruding from tube 104. A fixed left mark 166 and a fixed right mark 167 are attached to the base plate 102. Accordingly, when the web 116 swings, the marks 164 and 165 interrupt the light beam from the light source 169 and 170 to the photosensors 181 and 182, respectively. The point at which the marks 164 and 166 or 165 and 167 interrupt the light beam is approximately at the center of vibration of the web 116. However, a set of marks can be offset from the other place with respect to the vibration node. It is found

that with the angular deformation of the web 116 with respect to the holder 102, which is based on the Coriolis forces generated by the flow through the tube 104, a change in the time delay occurs between the overlap of the marks 164 and 166 or the marks 165 and 167. The time difference and the sign depend, with a fixed vibration range of the web 116, on the generated Coriolis forces in the direction of the vibration. The photoresistor 181 is connected directly to the reset terminal of the flip-flop 185 and connected to the reset terminal of the flip-flop 186 via an inverter 188. The photoresistor 182 is connected directly to the set side of the flip-flop 185 and via an inverter 189 to the set terminal of the flip-flop 186. Differentiation capacitors 191 and 192 are connected upstream of the reset inputs of flip-flops 185 and 186. Differentiation capacitors 193 and 194 are connected upstream of the set terminals of the flip-flops 185 and 186. If the marks 164 and 166 slide over one another, the photo resistor 181 thus generates a positive signal which resets the flip-flop 185. If the marks 165 and 167 slide one above the other, the photoresistor 182 also generates a positive signal in order to set the flip-flop 185. As a result, the flip-flop 185 is actuated in the period when the marks are superimposed. When the marks 164 and 166 or 165 and 167 are pulled apart, the photoresistors 181 and 182 generate a smear or a negative signal which actuates the flip-flop 186 via the inverters 188 and 189. As a result, the flip-flop is operated in the period when the marks are apart. The output signals from flip-flops 185 and 186 are applied to the inputs of a differential counter 198 via resistors 195 and 196, respectively. A capacitor 200 is connected from the positive input to the output thereof via the integrator. A capacitor 201 is connected between the negative input of the integrator and the earth.

The output signal B from the integrator 198 thus depends on the periods during which the flip-flops 185 and 186 are actuated. In the case where the land 116 only swings, without deformation, the time difference between sliding over and pulling the marks apart will be substantially constant and the input signals to the integrator 198 will be substantially identical so that no signal B will be generated. On the other hand, if Coriolis forces are generated, the web is deformed clockwise to one shock of the vibrations and counterclockwise to the other shock. Thus, the stacking of the marks on one side takes place earlier on one side and later on the other side, while the other brands are later on the first side and earlier on the other side. The flip-flops 185 and 186 are therefore not actuated for the same time, and the integrator 198 generates a suitable DC signal B with a positive or negative sign, which depends on the phase of the deformation of the leg with respect to the up or down shock.

Another arrangement is shown in Fig. 12 to achieve the same result. Strain gauges 204 and 205 are arranged in addition to the intersection points of the leg 108 and the web 116 or the leg 109 or the web 116. The strain gauges 204 and 205, which can be regarded as variable resistors, are connected together with the resistors 207 and 208 to form a bridge circuit which is connected to an AC differential amplifier 210. In the case of a pure oscillation of the U-shaped tube 104, the resistance value of the strain gauges 204 and 205 changes in the same way, whereby essentially identical input signals are applied to the amplifier 210. In case of deformation caused by the Coriolis forces

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the resistance of one strain gauge 204 and 205 is increased while the other is decreased, causing different input signals to amplifier 210. The amplifier 210 outputs an output signal in the form of an AC voltage signal which is proportional in value and sign to the different stresses acting on the strain gauges 204 and 205.

The output signal from the amplifier 210 is fed to a synchronous demodulator 211 which, in conjunction with the signal A, emits a DC voltage signal which is proportional in value and sign to the deformation of the egg-shaped tube 104, which is attributable to the Coriolis forces acting on it. The synchronous demodulator 211 is similar to the synchronous demodulator 162 described above and is explained in more detail below with reference to FIG. 14.

A similar arrangement for generating the signal B is shown in FIG. In this case, however, a pivot member 215 is fastened in the middle to the web 116 and carries a rod 217 which acts as an inertial mass and which is freely rotatable about the pivot member 215 and is in equilibrium. Crystals 219 and 220 are arranged between the rod 217 and the rod 116. Thus, if the web 116 is subject to simple vibration, the rod 217 only follows the vibration without tending to rotate about the pivot member 215. In the event of deformation of the U-shaped tube 104, however, the leg tends to rotate with respect to the rod 217. This causes forces in opposite directions on the crystals

219 and 220 applied, and thus because of the piezoelectric effect signals from the crystals 219 and

220 delivered. The output signals from the crystals 219 and 220 are output to an AC differential amplifier 222. The AC voltage differential amplifier 222 is connected downstream of a synchronous demodulator 224 in order to generate, in conjunction with the signal A, a DC voltage signal B with a value and a sign which are proportional to the deformation of the U-shaped tube 104. Note that a voltage source and strain gauges can be used in place of crystals 219 and 220.

14, the demodulators 162, 211 and 224 will be described in detail. As shown, the input signal is supplied in the form of an AC signal on a line 225 to a primary winding 227 of a transformer. The commonly grounded secondary windings 228 are wound in opposite directions, as indicated by the polarity. Thus, the output signals output at the opposite ends of the secondary winding 228 are 180 ° out of phase. Switching elements in the form of field effect transistors 230 and 231 are switched on in the outputs of the secondary windings 228. A comparator 233, to which the signal A is present, outputs positive or negative signals depending on the ratio of the signal A to the reference voltage VR3. The output signal of the comparator 233 is thus a square wave signal with positi641 277

ven or negative sign and is applied to an inverter 235, which inverts the signal. Part of the square wave signal turns transistor 230 on and blocks transistor 231, and the other part turns transistor 231 on and blocks transistor 230. As a result, part of the input signal 225 that is in phase with signal A becomes an RC Circuit 237, which is formed by a resistor 238 and a capacitor 239, is supplied. This RC circuit 237 outputs a DC voltage signal which is proportional to the root mean square of the input signal to the filter 237. This DC output signal forms the display as described above, i.e. a DC signal that is proportional to the flow through the U-shaped tube 104.

The flow meter 100 described above uses deflection sensors 133 and 134 to sense the value and sign of a slight sluggish deflection of the U-shaped tube 104 due to the action of Coriolis forces and to provide a DC signal with a sign and a value, which is proportional to this deflection. The DC voltage signal, signal B, is essentially a feedback signal which regulates the compensating force which is generated by the drive coils 131 and 132 in order to generate a counterforce and thus prevent a noticeable deformation outside the deformation sensed at the beginning. The sensor coils 128 and 129 also output a signal A, namely a signal that is in phase with the Coriolis forces, in order thus to precisely control the drive coils 131 and 132, to precisely synchronize the output signal of the AC amplifier 135 in a U-shaped manner vibrate formed tube 104 and accurately demodulate the synchronous signal from drive coils 131 and 132 to produce a DC output signal proportional to the flow rate.

Although the two preferred devices for measuring Coriolis forces are described in detail above, e.g. there are other, less suitable means of allowing the tube to deflect elastically and measuring the deflection, or equalizing the forces to eliminate the deflection and measuring the compensating forces. When using a permanently mounted U-shaped tube that is essentially free of pressure-sensitive connection points or swivel devices,

the pipe can be easily vibrated or deflected, and thus the flow can be determined over a wide range. The U-pipe is composed of corner pieces and pipe pieces that are soldered or brazed or welded together. These soft or hard soldered or welded connection points are not sensitive to the pressure of the flowing material.

In contrast, those connection points are sensitive to pressure by means of rubber sleeves or bellows. The properties of the U-tube are influenced by such connecting points, so that an accurate measurement of the Coriolis force is not possible due to the measurement of the deflection.

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Claims (29)

641 277 2nd PATENT CLAIMS 1. A method for measuring the flow rate by measuring the Coriolis forces which are generated by the flow of material through a moving tube, characterized in that the material flows through a U-shaped tube free of pressure-sensitive connection points, which at its free leg ends on a holder (12) is rigidly fixed so that the U-tube is caused to oscillate about an oscillation axis (WW, W'-W ') that passes through the inlet and outlet ends, due to the material flowing through the oscillating U-tube Coriolis forces are generated and that the Coriolis forces that tend to deform the U-tube about a bending axis (0-0) that is perpendicular to the vibration axis of the U-tube and in the plane of the U-tube are measured, wherein the U-tube has different resonance frequencies with respect to the vibration and bending axis (WW, 0-0), and the value of the Coriolis forces depends on the amount of material flowing through the U-tube is. 2. Device for performing the method according to claim 1, characterized by a holder (12, 102), a U-shaped tube (14, 104) which is free of pressure-sensitive connection points and which is attached to its free leg ends on the holder and with its other end from The holder protrudes in such a way that the U-tube can oscillate with respect to the axis of oscillation (WW; W'-W '), which runs through the connection points of the free leg ends with the holder, and with respect to the bending axis (0-0), which bending axis ( 0-0) is the axis of symmetry of the U-tube and extends transversely to the axis of vibration, the U-tube having different resonance frequencies with respect to the axis of vibration and bending, by an excitation device (23, 24, 25; 118, 120, 122) to the U -Pipe (14, 104) to vibrate the axis of oscillation (WW; W'-W ') and by feelers (43, 44; 128, 129) to measure the value of the Coriolis forces. 3. The method according to claim 1, characterized in that the value of the Coriolis forces by determining the time delay between the passage of the one leg of the U-tube through a plane which essentially passes through the center of vibration and the passage of the other leg of the U- Tube is measured through this plane. 4. The method according to claim 1, characterized in that the value of the Coriolis forces which deform the U-tube (104) around the bending axis is determined by measuring the angular deflection of the U-tube around the bending axis. 5. The method according to claim 4, characterized in that the U-tube and the material located therein is vibrated with its resonance frequency and with a constant amplitude. 6. The method according to claim 5, characterized in that the deflection angle by measuring the time difference between the passage of a part of the U-tube through a plane at the center of the oscillation, which plane contains the axis of vibration (W'-W), and the passage of a symmetrically opposite second part of the U-tube is determined by this plane. 7. The method according to claim 1, characterized in that the value of the Coriolis forces is measured by sensing the beginning deformation of the U-tube around the bending axis, that a force which counteracts the Coriolis force is generated as a function of the sensed beginning deformation, to limit the deformation to an initial deformation and to measure the value of the counterforce to determine the flow rate. 8. The method according to claim 1, characterized in that a spring lever with a resonance frequency, which is identical to that of the U-tube, is arranged next to the free leg ends on the U-tube and oscillates out of phase with the U-tube. 9. The method according to claim 8, characterized in that the tube and the spring lever by generating a force between a magnet (25) which is fixed to the tube (14) or on the spring lever (22), and a drive coil (24) on the spring lever (22) or on the tube (14) is set to vibrate. 10. The method according to claim 7, characterized in that the beginning deformation by measuring the time difference between the passage of a part of the U-tube through a plane that contains the center of the vibration, and the passage of a symmetrically opposite part of the U-tube this level is scanned. 11. The method according to claim 7, characterized in that the deformation is sensed by strain gauges which are attached to the U-tube at locations symmetrical with respect to the bending axis. 12. The method according to claim 7, characterized in that the deformation of the tube is sensed by quartz crystals, which between the tube and an inertia-generating rod which is pivotally attached to the tube on the bending axis, the quartz crystals being symmetrical with respect to the bending axis of the Pipe are arranged. 13. The apparatus according to claim 2, characterized in that the resonance frequency of the vibration of the U-tube (14,104) around the vibration axis (WW; W'-W ') is lower than the resonance frequency of the vibration of the U-tube around the bending axis (0 -0). M.Device according to claim 2, characterized in that the excitation device (23,24,25) a magnet (25) which is mounted on the U-tube (14) or on a fixed structure next to the U-tube, a sensor coil ( 23) and a drive coil (24), which are mounted on the fixed structure or on the tube (14), and have a current source (27), in response to a signal determined by the movement of the magnet (25) with respect to the sensor coil (23) to supply an electric current to the drive coil (24). 15. The apparatus according to claim 2, characterized in that a spring lever (22) is provided, the resonance frequency is equal to that of the U-tube (14). 16. The apparatus according to claim 15, characterized in that on the spring lever (22) or U-tube (14), a sensor coil (23) and a drive coil (24) are arranged, and that a magnet (25) next to the sensor coil ( 23) and the drive coil (24) is arranged on the spring lever or U-tube, the magnet (25), the sensor coil (23) and the drive coil (24) in conjunction with an amplifier (41) and peak value detector (39 ) form the drive in order to set the U-tube (14) and the spring lever (22) out of phase with one another about the oscillation axis (WW). 17. The apparatus according to claim 2, characterized in that the first and second sensors (43,44) next to the U-tube (14) on the symmetrical with respect to the bending axis (0-0) and in the center plane of the U-tube (14) lying positions, each sensor (43,44) is intended to emit a signal when the adjacent section of the U-tube passes the center plane of vibration and that a timer (33) for measuring the time delay between those by the sensors (43,44) is provided to determine the / flow rate as a directly proportional function of the time delay. 18. The apparatus according to claim 17, characterized in 5 10th 15 20th 25th 30th 35 40 45 50 55 60 OD 3rd 641 277 net that the timer (33) is designed to subtract the time delay during the vibration of the U-tube in one direction from the time delay of the vibration of the U-tube in the other direction. 19. The device according to claim 17, characterized in that the output of the first and second sensors (43, 44) is in each case electrically connected to a series-connected inverter pair (47, 48 and 49, 50), that the outputs of the first inverters ( 47, 48) are each connected to the set and reset inputs of a first flip-flop (60) and the outputs of the second inverter (49, 50) are each connected to the set and reset inputs of a second flip-flop (54) that the Output of the first flip-flop (60) is connected to the input of a first gate (66) and the output of the second flip-flop (54) to the input of a second gate (64) that the other inputs of the first and second gates are each connected to an oscillator (67), and that the output of the first gate (66) to a clock input of an up / down counter (70) and the output of the second gate to the other input of the up / down counter (70 ) is connected, the up / down counter (70) depending is activated by the time difference between the activation of the first and second sensors (43, 44), and the count in ascending order when the U-tube vibrates in one direction and the count in the descending order when the U- Tube in the opposite direction. 20. The apparatus according to claim 19, characterized in that a display device (80) for transmitting the output signals of the up / down counter (70) to a display register (80), which transmission when a number of vibrations of the U-tube as a display the flow rate is passed through it, and a signal generator (74) is provided for resetting the up / down counter (70) after the transmission of the output signal of the counter to the display register. 21. The apparatus according to claim 19, characterized in that the output of the up / down counter (70) is connected to a digital counter (82), that the digital counter (82) is designed to a time base from an oscillator oscillating at a fixed frequency derive, and that the output of the digital counter (82) is connected to a display device (87) for displaying the total flow rate. 22. The apparatus according to claim 17, characterized in that a frequency counter (96) for measuring the vibrations of the U-tube (14) and for displaying the oscillation period as a function of the density of the fluid flowing through the U-tube is provided. 23. The device according to claim 2, characterized in that the sensor has a scanning device to measure the angular deflection of the U-tube (14) as a result of the elastic deformation of the U-tube (14) around the bending axis (0-0) , whereby the flow rate of the material can be determined by the value of the deflection of the U-tube around the bending axis (0-0). 24. The device according to claim 2 or 23, characterized in that the excitation device (23, 24, 25) further comprises a detector (39) to determine the peak value of the sensor coil (23) as a function of the relative movement between the sensor coil (23) and Magnet (25) generated signal and to deliver a current to the drive coil, such that a preselected vibration amplitude is maintained. 25. The device according to claim 2, characterized in that the excitation device (118, 120) is designed to vibrate the U-tube (104) with constant frequency and amplitude, and that sensors (133, 134) are provided to sense the deformation of the U-tube (104) around the bending axis (0'-0 '), further characterized by a torque-generating device (125, 131, 128, and 126, 132, 129) acting on the sensor (133, 134) in order to generate a counterforce to limit the deformation and by a measuring device to determine the counterforce, the flow rate of the material being determined by the value of the counterforce (FIG. 9). 26. The device according to claim 2 or 25, characterized in that the sensors for sensing the deformation of the U-tube (104) around the bending axis are deflection sensors (133, 134), each of which is round next to the legs of the U-tube (104) at the center of vibration are arranged around the vibration axis (W'-W '). 27. The device according to claim 26, characterized in that the sensors (133, 134) each contain a pair of brands (164, 166; 165, 167), of which one brand (166, 167) is permanently mounted and the other (164, 165) on one Leg of the U-tube (104) is fastened such that it overlaps the fixed mark (166, 167) approximately at the center of the vibration, that a light source (169, 170) is arranged on one side of the mark, and that a light-sensitive detector (181 , 182) is arranged on the other side of the marks, wherein the movement can be sensed by covering the light source by the marks (FIG. 11). 28. The apparatus of claim 2 or 25, characterized in that the detector for sensing the deformation of the U-tube around the bending axis has a pair of strain gauges (204, 205), each on the U-tube (104) next to each intersection of the legs are arranged with the web (116) of the U-tube, and that the strain gauges (204, 205) are part of a bridge circuit, the output signal of which is proportional to the deformation of the U-tube around the bending axis (FIG. 12). 29. The device according to claim 2 or 25, characterized in that the sensor for sensing the deformation of the U-tube (104) around the bending axis has a rod (217) generating an inertial force, which is symmetrical and pivotable about the center of the web (116 ) of the U-tube and has a pair of force sensors (219, 220), which are each attached to one end of the rod (217) and lie next to the web, (16) of the U-tube (104) (Fig. 13 ).