CORIOLIS EFFECT MASS FLOW METER

Abstract: A Coriolis effect mass flow meter for measuring mass material flow in a conduit. The provided meter may be clamped directly onto an existing pipe or other conduit without diversion of the flow. The meter provides a driver (20), such as a magnetostrictive driver, to oscillate a section of pipe between two supports (12, 14). The driver (20) is mounted at or near an anti-node of the second harmonic mode of the natural frequency of the pipe section. A sensor (30) mounted adjacent the driver operates through a control circuit (Fig. 5) to control the frequency of oscillation of the pipe section. A second sensor (32), such as an accelerometer, is mounted at the node point of the second harmonic mode of the natural frequency of the pipe section during zero flow, (zero flow node point). The second sensor measures the amplitude of displacement of the zero flow node point due to the Coriolis effect forces from the mass of the material flowing through the oscillating pipe. This measurement is indicative of the mass flow rate of the material flowing through the pipe. The meter is not dependent upon phase shift detection and is not susceptible to extraneous noise and does not require a complicated mounting. In alternative embodiments, the meter is prefabricated on a section of pipe which can then be installed in a pipeline as an off the shelf item.

Description: CORIOLIS EFFECT MASS FLOW METER BACKGROUND OF THE INVENTION 1. Field of the Invention; The present invention relates to the field of Coriolis effect flow meters. It further relates to the provision of a Coriolis effect flow meter for measuring mass fluid flow in a tube or pipe. It still further relates to the provision of flow meter devices that are affixed to existing tubes or pipes to operate them as Coriolis flow meters. 2. Statement of the Problem; Mass flow rate measurement devices utilizing Coriolis force effects are well known in the art. It is known that the flow of a fluid or other material through an oscillating conduit produces Coriolis forces which are perpendicular to both the velocity of the mass moving through the conduit and the angular velocity vector of the oscillation of the conduit. The magnitude of the Coriolis forces is related to the material mass flow rate as a function of the angular velocity of the conduit. Typically, prior art flow meters use one or two flow tubes to direct material flow through a pipe. These tubes may be continuously curved and mounted in the flow line or attached to a substantially rigid heavy support. The tubes are normally oscillated by an electromagnetic drive. The Coriolis effect forces resulting from the mass of the material flowing through the oscillating tubes cause a twisting motion in the tubes. The twisting of the tubes is measured at symmetrical points on the tubes by position or velocity sensors. The time differential between the movements of the tube elements at spaced locations is used for the determination of the mass flow rate. Other variables resulting from the phase shift of the oscillation have also been used for this determinatio . The prior art flow meters have a number of disadvantages. They all require a diversion of the material flow into specially provided flow tubes of the meters. This creates a pressure drop and reduces the volume of material flow through the pipe system of which the meter is a part. Many prior art flow meters are dependent on phase shift measurements of the oscillation or twisting of the flow tubes. This normally requires isolation of the flow tubes from outside vibrations. The use of double tubes increases accuracy by reducing errors from the outside vibrations. Mounting the tubes on exterior support structures can itself cause vibration and noise to be transmitted through to the tubes, such as on a ship or other vibrating structure. There presently exists a need for a flow meter for measuring the mass flow rate of material within a pipe or other conduit with only a minimal modification of the pipe or conduit being required to accommodate the meter. There is also need for the provision of a meter that will not create additional pressure drops within the pipe or reduce the flow of material and that is not highly susceptible to extraneous noise and vibration. SUMMARY OF THE INVENTION The present invention provides an improved method of and apparatus for measuring the-mass flow rate of materials through a pipe or other conduit. The provided meter measures the mass flow rate by measuring the Coriolis force effects of the flowing material undergoing oscillation. The apparatus comprising the flow meter of the invention may be clamped directly, onto an existing pipe system. The apparatus alternatively may be supplied as an off-the- shelf flow meter by incorporating it into an existing pipe system. The flow meter of the present invention does not require external supports to isolate the meter from extraneous vibration. External supports may be added where the length of the section of pipe is too long for a practical flow meter to operate efficiently. In these situations, additional external supports may be installed. These additional external supports are designed according to the particulars of the intended specific use. The meter of the present invention uses a driver, for instance a agnetostrictive driver, that oscillates a section of pipe at a harmonic frequency, such as the second harmonic, of the pipe section's natural frequency. The driver which generates the vibrating motion at the second harmonic frequency of the tube section is clamped onto the pipe at or near an anti-node of the second harmonic of the natural frequency or at any other location except a node of the second harmonic of the natural frequency. No external supports are used in mounting the driver which is controlled through a feedback circuit to maintain the desired frequency and amplitude of oscillation. A motion sensor, such as an accelero eter, is mounted adjacent the driver and comprises part of a feedback circuit for controlling the driver. In an alternative embodiment an electromagnetic coil supported by an external support is used to vibrate the pipe. Another motion sensor, preferably an accelerometer, is mounted at a location comprising a node of the second harmonic of the natural frequency of the vibration of the pipe for a zero flow rate of material in the pipe. This node is hereinafter referred to as the "zero flow node". No external supports are required in mounting this sensor apparatus in one preferred embodiment. The Coriolis forces resulting from material flowing through the oscillating pipe cause the zero flow node to be displaced in a direction perpendicular to the direction of material flow. The vector component of angular velocity of the material flowing through the pipe creates forces against the wall of the pipe. These forces displace the position of the zero flow node location of the pipe in a direction transversely to the location of the node without any material flow. Since the pipe achieves two extreme positions during each vibration cycle, one driven and one non-driven, the zero flow node pipe location shifts transversely twice during each cycle. The sensor mounted at the zero flow node translates this transverse displacement into a position, velocity or acceleration signal which is proportional to mass flow rate. From this transverse displacement a measure of the mass flow rate of the material through the vibrating pipe can be derived. Since the motion sensor measures only the acceleration and therefore the frequency dependent amplitude of the transverse displacement of the zero flow node location, the measurement is not dependent on phase shift between two signals as is often done in prior art arrangements. This allows the use of electrical filtering to reduce the susceptibility of the motion sensor to extraneous noise and vibration. Thus, the elements of the flow meter do not have to be isolated and can be mounted directly onto the pipe. This eliminates additional pressure drops in the pipe and the need for a complicated mounting of the flow meter. .. The flow meter of the present invention can be mounted directly onto existing pipes or, alternatively, the flow meter can be prefabricated and incorporated into a pipe system by cutting out a section of pipe and mounting the prefabricated unit therein. Also, the elements of the flow meter can be mounted using external supports and electromagnetic coils to drive the pipe and to measure the mass flow rate. The flow meter of the present invention can be used either on substantially straight or on curved pipes. The present invention also provides, if desired, additional sensors mounted on the pipe supports to detect and cancel extraneous noise to provide higher accuracy of measurement. These and other features of the present invention are evident from the ensuing description of possible exemplary preferred embodiments taken in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a schematic representation of one possible exemplary preferred embodiment of the present invention; FIG. 2 shows a basic zero flow amplitude of oscillation curve of the second harmonic of the natural frequency of a pipe section and the amplitude of oscillation .curves due to the Coriolis effect forces as material flows through the pipe; FIG. 3 is a side cut-away view of a magnetostrictive driver of one possible exemplary preferred embodiment of the present invention; FIG. 4 is a side cut-away view of a electromagnetic drive comprising a second possible exemplary preferred embodiment of the present invention; FIGS. 5 and 6 show two different embodiments of the mass flow meter; and FIG. 7 shows an alternative embodiment of control circuitry for driver 20. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The present invention provides apparatus comprising and a method of operating a mass flow meter for measuring the mass flow rates of material through a conduit, such as a pipe or tube. The provided mass flow meter can be mounted onto existing pipes without diverting or restricting the material flow or requiring complicated mounting procedures. Alternatively, the flow meter of the present invention can be fabricated as a unit to be installed into an existing pipe system. The flow meter of the invention is operable on various sizes and shapes of pipes and in most operating conditions. The conduits with which the flow meter is utilized are herein referred to as pipes. However, the present invention is not meant to be limited to this description. Other types of closed conduits, such as tubes and the like, are within the claimed inventive concept. One possible exemplary preferred embodiment of the present invention is illustrated in FIG. 1. It is to be expressly understood that this descriptive embodiment is for explanatory purposes only and is not meant to limit the scope of the claimed inventive concept. Other embodiments are considered to be within the scope of the present invention. The disclosed meter is affixed to tubes or pipes which are capable of withstanding the stresses generated by the combined effects of the vibration and the Coriolis forces. Such materials are well known in the art. Overview of the system; A section of pipe 10 on FIG. 1 is supported by elements 12, 14. The distance between these elements determines the frequency at which pipe 10 vibrates since the distance is one wave length of the frequency of vibration. In instances where the length of pipe 10 is too long for the flow meter to practically be operable, support(s) in addition to and in between elements 12 and 14 can be mounted on pipe 10 to define this section. The flow meter elements of the present invention are clamped onto pipe 10 without any substantial modifications or alterations of the pipe being required to measure the mass flow rate of the material being transported within the pipe. Pipe 10 is shown as a substantially straight tube of constant cross-section. It is to be understood that the flow meter of the present invention is usable on various shapes and configurations of tubes. Pipe 10 and supports 12, 14 can be pre-existing, such as in a pipeline or other industrial usage. The flow meter of FIG. 1 includes driver 20 which is clamped directly onto pipe 10 at or near an anti- node of the second harmonic of the natural frequency or at any other location except a node of the second harmonic of the natural frequency. Additional drivers, similar to driver 20 can also be clamped onto pipe 10 to add symmetry or to equalize the loading on the pipe. However, the system of the present invention is operable with only one driver, as shown. Driver 20 includes a feedback circuit which includes motion sensor 30 which is mounted on the pipe directly opposite driver 20 or near driver 20 or affixed onto driver 20. The flow meter elements further include a second motion sensor 32 mounted onto pipe 10 at a zero flow vibration node location. A third motion sensor 34 may be mounted onto one of the supports, such as support 14. Motion sensors 30 and 32 are affixed directly to pipe 10. Counterweight 40 may be mounted on pipe 10 at a predetermined location, such as a harmonic anti-node of the natural vibration frequency of pipe 10, to balance the load created by driver 20. If desired, a " second driver may be mounted at this location, or the counterweight 40 or a second driver can be eliminated. In a second possible preferred embodiment, the flow meter is prefabricated in advance as a specially provided pipe section which is then incorporated into an existing pipe system. A section of the existing pipe is removed and the prefabricated tube with the flow meter elements of FIG. 1 already affixed to it is inserted in place of the removed section of pipe. This embodiment can be stocked as an off the shelf item ready for installation. The operation of this flow meter is similar to the one described above. Other possible exemplary embodiments include a flowmeter similar in operation as the above-described system but having a driver that is externally supported instead of being clamped directly onto pipe 10. Alternatively, the driver could toe clamped onto the pipe as shown on FIG. 1 with the sensors being mounted on external supports. The flow meter of the present invention can also include supports for isolating a length of a pipe that has long unsupported sections. This may be necessary to isolate the flow meter from extraneous noise or to reduce the resonant frequency of the pipe section to a practical value. These additional supports are of a well known design. However, in the preferred embodiment, the flow meter of the present invention can be clamped directly onto existing pipelines without additional supports. Operation of the system; Pipe 10, between supports 12, 14, is vibrated by driver 20 at a harmonic, such as the second, of the natural frequency of pipe section 10. This frequency is a function " of the characteristics of the pipe, including its length, mass, physical properties and the like. The amplitude curve 200 of FIG. 2 portrays the zero flow state, of pipe 10 vibrating at its second harmonic frequency. This frequency of vibration is maintained by driver 20 and accelerometer 30 via a feedback circuit, as later described. Curve 200 has zero amplitude at each end where the pipe is fixed by supports 12, 14 and at the zero flow node location 202 if there is no flow. Motion sensor 32 of FIG. 1 is affixed to pipe 10 at location 202. Sensor 32 is illustrated in FIG. 1 as being at the midpoint of pipe 10 between supports 12, 14. However, zero flow node location 202 and sensor 32 may be at various locations between the supports 12 and 14. This is a result of a possible asymmetrical loading on pipe 10, physical characteristics of the pipe, the use or nonuse of additional drivers and counterweights, and other factors. The peak amplitudes of curve 200 occur at anti- nodes 204, 206. Driver 20 is preferably mounted on pipe 10 at or near anti-node 204 and counterweight 40, which may be a second driver, may be mounted at or near anti-node 206 to equalize the driving forces and p pe loading. Driver 20 can be mounted at any location except zero flow node location 202. Locating the driver at an anti-node is preferable in order to enhance the efficiency of operation. Driver 20 applies a transverse force to pipe 10 and then releases this force to cause pipe 10 to oscillate. This is indicated by amplitude curve 200 during the forced portion of the cycle and by amplitude curve 200' during the unforced portion of the cycle. Anti-nodes 204, 206 are reversed in amplitude in every cycle and have locations at 204' 206' during the unforced portion of the cycle. The vibration of pipe 10 with material flowing therethrough produces Coriolis forces on each element of the pipe. The amplitude curves 210, 220 of the pipe with fluid,.flow are illustrated in FIG. 2. The pipe 10 deflection amplitudes are exaggerated on FIG. 2 in order to explain the operation of the system of FIG. 1. The effect of the Coriolis forces on pipe 10 causes amplitude curve 210 (corresponding to the first portion of the driving cycle) to shift to the left as compared to amplitude curve 200 of the zero flow state. The material flowing in pipe 10 is resistive to effects imparted by the vibrating pipe. The initial portion of curve 210 is reduced in amplitude as compared to curve 200 due to the Coriolis force effects of the material acting against the walls of pipe 10. This causes the node (the point of zero amplitude) of amplitude curve 210 to shift to position 212. Likewise, the Coriolis force effects on pipe 10 during the second portion of the cycle result in amplitude curve 220 of the pipe. Node 222 (point of zero amplitude) of curve 220 leads node 202 of curve 200. The cyclical longitudinal displacement of node 212 and node 222 creates a cyclical transverse amplitude displacement of the zero flow nodal location 202 (where sensor 32 is located) of pipe 10. This transverse displacement, illustrated in FIG. 2, occurs between point 218 of curve 210, showing the displacement of curve 210 from zero flow node location 202, and point 228 of curve 220 showing the displacement of curve 220 from zero flow node location 202. This cyclical transverse displacement of the zero flow node location is due to the Coriolis force effects " of the fluid flow through vibrating pipe 10. Since the Coriolis force effects are due to the mass of the material flowing in pipe 10, the measured transverse acceleration and the displacement derived from it is directly indicative of the mass flow rate of the material. Motion sensor 32 is mounted at the zero flow nodal location 202 on pipe 10 to measure the amplitude of the cyclical transverse displacement of pipe 10. In one possible preferred embodiment, sensor 32 is an accelerometer that measures the acceleration of the material mass at zero flow node location 202. Accelerometer 32 is mounted directly onto pipe 10 and—unlike prior art motion detectors—does not require a stable external point of reference. The signal output of accelerometer 32 can be processed to provide the mass flow rate, total amount of mass, and other measurement information. This signal is dependent only upon the amplitude of the transverse displacement of pipe 10 at the zero flow nodal mounting location 202 and does not require the measurement of phase shifts. This provides an accurate, dependable measurement and is less susceptible to extraneous noise and vibrations. Sensor 32 cooperates with sensor 34 mounted on support 14 to eliminate or reduce noise in the signal output of sensor 32. The operation of the sensors and related circuitry is subsequently discussed in detail. It should be clearly understood that the amplitude measured by sensor 32 is not directly proportional to mass flow rate, it is only indicative of it. The reason for this is that accelerometer 32 produces a signal which is proportional to acceleration, while the mass flow rate is proportional to displacement. Displacement is the second integral of acceleration. Therefore to read " a mass flow rate at any pipe frequency (which is related to and varies with the density of the material in the pipe) , the acceleration measured by sensor 32 is modified according to the frequency of the pipe vibration. The driving mechanism 20; Driver 20 oscillates pipe 10 at a harmonic frequency, such as the second, of the natural frequency of pipe 10. Several mechanisms are shown to perform this function. One possible embodiment of driver 20 is illustrated in FIG. 3. Driver 300 is a magnetostrictive transducer, capable of being clamped directly onto pipe 10 and generating sufficient force to oscillate pipe 10. Driver 300 can also be used as a sensor, as later discussed. The exact parameters of the driver are dependent upon the power, force, frequency, and displacements required for operation. However, the design of the driver of this embodiment is substantially the same for all variations. Driver 300 includes a cylindrical rod 302 formed of an alloy, such as TERFENOL-D, which is commercially available. Tubular permanent magnet 304 surrounds rod 302 to provide a magnetic bias field. Due to the reversible properties of the described embodiment, the driver can also function as a sensor to measure vibrational forces. Pre-stress is provided on driver 300 by die spring 322. Solenoid coil 306 is contained within permanent magnet 304 surrounding rod 302 to provide a driving magnetic field. The magnetic circuit is completed by soft iron caps 308, 310. Solenoid coil 306 and magnet 304 are both bonded to upper pole cap 310. Clamp assembly 312 mounts driver 300 onto pipe 10. Clamp assembly 312 includes upper mounting plate 314, and"lower mounting plate 316, each having arcuate portions sized to mate with pipe 10. Bolts 318 clamp mounting plates 314, 316 on pipe 10. Mass 320 is secured on driver 300 to provide an opposing mass to pipe 10 so that most of the energy produced by the driver is transferred to pipe 10. Connecting rod 324 constrains spring 322 to vertical movement. Outer shell 326 contains the interior of the driver as well as cooperating with end plate 328 to hold spring 322 in compression. Retaining ring 330 retains end plate 328 in place on shell 326. An alternating current is applied to coil 306 by the circuitry of FIGS. 5, 6, or 7 to provide a magnetic field to nickel alloy rod 302. This magnetic field having been added to the bias field of permanent magnet 304 causes rod 302 to elongate. When an alternating current is applied to coil 306, rod 302 elongates and returns back to its normal length at the frequency of the alternating current. A force is generated by the elongation of rod 302 which is transmitted through guide rod 324 and clamp assembly 312 to pipe 10. Mass 320 provides a reactionary force against rod 302 so the force from the elongation of rod 30 is transferred to pipe 10. As the current changes direction in the second half of the alternating current cycle, the driving magnetic field in coil 306 is reduced and rod 302 returns to its normal length. This removes the force from pipe 10. The cyclical changes in elongation of rod 302 create a driving force against pipe 10 to oscillate the pipe. The oscillation of pipe 10 can be controlled by controlling the amplitude and frequency of the drive current applied to coil 306. A feedback circuit is used to maintain the oscillation of pipe 10 at the correct frequency and at a necessary amplitude. Magnetostrictive driver 300 can also be used as a sensor for feedback purposes to control the amplitude and frequency of the driving force. In this embodiment the drive current to coil 306 can be periodically interrupted, for instance, every five to ten cycles. During each interruption, driver 300 operates as a signal detector. Rod 302 is then compressed by the oscillating pipe and counterweight 320. This compression generates an electromagnetic field in coil 306. The resultant voltage is sampled as driver 300 functions as a pickup sensor to control the frequency and amplitude of oscillation of pipe 10. Second preferred embodiment of the driver; A second possible exemplary preferred embodiment of driver 20 is illustrated in FIG. 4. Driver 400 utilizes an electromagnetic coil 406 to oscillate pipe 10. Driver 400 includes feedback coil 403 supported by bobbin 404 on an external support 401. Permanent magnet 409 is affixed onto pipe 10 with bobbin 404 slidably mounted thereover. Coil wires 403 are spirally wound about bobbin 404 to form a solenoid. Coil wires 403 extend from the solenoid to an input of amplifier 405. A second set of coil wires 406 are connected to the output of amplifier 405 and are spirally wound about bobbin 407. Bobbin 407 is slidably mounted over permanent magnet 408 which is also secured to pipe 10 to form a driving solenoid. Bobbin 407 is supported by external support 402. A signal from feedback coil 403 is applied to amplifier 405 which applies a drive signal to create a magnetic field in coil 406. By applying an alternating drive current to coil 406, the solenoid oscillates pipe 10. Feedback coil 403 and amplifier 405 maintain the circuit in oscillation at the second harmonic mode of the natural frequency of pipe 10. Description of FIG. 5 FIG. 5 discloses the details of circuitry that cooperates with accelerometers 30, 32, and 34 and driver 20 to vibrate pipe 10 of FIG. 1 at the second harmonics of its natural frequency and to generate the information regarding the flow of material in pipe 10. Accelerometers 30, 32 and 34 are the same elements shown on FIG. 1 and are used to supply signals to the circuitry of FIG. 5. Driver 20 of FIG. 1 is shown in the upper right hand corner of FIG. 5. This circuitry receives a signal from accelerometer 32 representing the movement of the zero flow node location of pipe 10 resulting from the Coriolis force generated by material flowing through pipe 10 as it is vibrated at a harmonic of its natural frequency. It processes this signal and converts it from a voltage to a frequency signal which may be used to determine the mass of the material flow through the pipe during a period of time. It further converts this signal from a voltage to a current modulated signal to indicate the mass flow rate of the material within pipe 10. The upper row of elements on FIG. 5 comprises a self-tuned oscillator which uses accelerometer 30 to detect the oscillation of pipe 10 caused by driver 20. The output of accelerometer 30 controls the frequency and amplitude of the signal applied to driver 20. As shown on FIG. 1, accelerometer 30 is attached to or associated with the same portion of pipe 10 to which driver 20 is attached or associated. The output of accelerometer 30 is applied over path 502 to amplifier 503 which applies its output signal over path 504 to Variable gain amplifier 506. Amplifier 506 has an internal reference potential representing the maximum amplitude of the output signal to be applied to path 507. Amplifier 506 receives the output of amplifier 503 and applies to path 507 an .output signal having the desired controlled amplitude. This controlled signal is applied to power amplifier 508 which applies over path 509 to driver 20 a signal of the required controlled amplitude to vibrate pipe 10 at a harmonic of its natural frequency. The middle row of elements on FIG. 5, beginning with accelerometers 32 and 34 on the left and extending to elements 540 and 541 on the right, detect the amplitude of the movement of the zero flow node location of pipe 10 associated with accelerometer 32 and apply a frequency modulated signal to path 524 and a current modulated signal to path 527. Accelerometer 32 drives amplifier 513 over path 511 which applies an amplified signal over path 515 to the non-inverting input of amplifier 536. Accelerometer 34 is connected to the outside environment, such as the foundation to which clamp 14 of FIG. 1 is mounted in order to detect external noise which might be imparted to pipe 10. The output of accelerometer 34 is applied over path 531 to amplifier 533 which applies its output over path 537 to the inverting input of amplifier 536. The gain of amplifier 533 is adjusted so as to apply to the inverting input of amplifier 534 a noise signal whose amplitude matches the component of the noise signal picked up by accelerometer 32 and applied to path 515. Amplifier 536 reduces the noise component of signal 515 and applies a signal over path 538 to band pass filter 516. Band pass filter 516 filters out other unwanted " frequencies so that its output on path 517 has only the desirable and useful frequency components of the signal originally generated by accelerometer 32. This filtered signal on path 517 is applied to the input of synchronous demodulator 518 which also receives on path 507 an input representing the drive signal. Synchronous demodulator 518 receives both the drive signal on path 507 and the filtered signal on path 517 and generates an output signal which contains only those frequency elements which are associated with the natural resonant frequency of pipe 10. Amplifier/filter 521 amplifies and further filters the signal on path 519 and its output signal 522 represents a mass flow rate signal which is applied to voltage-to-frequency converter 523 and to voltage-to-current converter 526. Element 523 converts the signal on path 522 from a voltage to a proportional frequency signal which is applied over path 524 to totalizer 540 which integrates the received signal. The signal on path 524 can also be applied to external devices. Signal 522 is also applied to voltage to current converter 526 whose output 527 is applied to indicator 541. Signal 527 comprises a current that is proportional to the mass flow rate and its receipt permits element 541 to indicate on path 543 the mass flow rate of the material in pipe 10. Description of FIG. 6 FIG. 6 discloses details of circuitry comparable to but an alternative to that of FIG. 5. The circuitry of FIG. 6 receives output signals of accelerometers 30, 32 and 34, generates a signal that causes driver 20 to oscillate pipe 10 at a harmonic of its natural frequency, and generates signals that cause totalizer 540 to represent the mass flow total over a period of time and to cause element 541 to generate an output signal representing the mass flow rate within pipe 10. The circuitry of FIG. 6 uses the switched capacitor filters (SCF) 650 and 658 together with phase lock loop (PLL) 651 instead of the band pass filter 516 and the synchronous detector 518 of FIG. 5. In order to facilitate a comparison of the circuitry of FIGS. 5 and 6, elements on FIG. 6 which are identical to those on FIG. 5 are designated in a corresponding manner with numbers in the 500 series while elements on FIG 6 that are not shown on FIG. 5 are designated with reference numbers in the 600 series. Accelerometers 30, 32 and 34 and driver 20 are identically designated on both FIGS. 5 and 6 and these elements perform the same functions as already described. . Accelerometer 30 and amplifier 503 function in the manner of FIG. 5 to detect and amplify a signal indicative of the motion of the portion of the that is vibrated by driver 20. This signal is applied over path 504 to the input of switched capacitor filter 650 and to an input of phase lock loop 651. The switched capacitor filter 650 functions as subsequently described to apply a band pass filtered signal over path 663 to the input of amplifier 506 which functions as described for FIG. 5 as a variable gain amplifier to control and limit the amplitude of the signal applied to driver 20. The output of amplifier 506 is applied over path 507 to power amplifier 508 which applies a drive signal over path 509 to driver 20. As described for FIG. 5, accelerometers 32 and 34, together with their associated circuitry including noise cancellation amplifier 536, apply a signal over path 538 to switched capacitor filter 658. Signal 538 represents the detected movement of the zero flow node portion of pipe 10 associated with accelerometer 32 caused by the combined effect of driver 20 and the Coriolis force resulting from the flow of material within pipe 10 as the pipe is vibrated at a harmonic of its natural frequency. Signal 538 is applied to switched capacitor filter 658 which filters it and applies a band pass filtered signal over path 659 to amplifier/filter 521. Element 521 operates in a manner similar to that already described on FIG. 5 to drive voltage to frequency converter 523 and voltage to current converter 526. These elements cause totalizer 540 and indicator 541 to provide outputs representing the total mass flow on path 524 and of the mass flow rate on path 543. SCF 650 and PLL 651 cooperate with voltage controlled oscillator 653 so that switched capacitor filter 650 can efficiently filter the signal received on path 504. In order to do this, switched capacitor filter 650 must receive a clock signal that is a controlled multiple of the frequency of the input signal on path 504. The signal on path 504 is applied to both SCF 650 and PLL 561. PLL 651 detects the frequency and phase of the signal on path 504 and path 654 and, by means of its voltage controlled oscillator (VCO) 653, applies a clock signal to path 657 that is the required multiple of the frequency of the signal on path 504. PLL 651 locks onto signals that are 90 degrees shifted relative to each other on paths 504 and 654. When SCF 650 is tuned by the clock signal on path 657 to the exact frequency of the signal on path 504, the low pass output 654 of the switch capacitor filter is in this desirable 90 " phase shift situation. PLL 650 is tuned to close the loop by providing the desired clock frequency on path 657 and it maintains this relationship through the operating range of the flow meter regardless of any possible variations of frequencies of input signal 504. The signal on path 655 from PLL 651 is filtered by low pass filter 652 and applied over path 656 to VCO 653 to provide an input signal representing the frequency of the input signal on path 504. The circuitry on FIG. 6 including SCF 650, PLL 651 and low pass filter (LPF) 652 is similar to that shown in the article entitled, "Clock Tracks Switch-Cap Filter" by Marcus Julian on page 131 of Electronic Design dated January 12, 1989. Description of FIG. 7 FIG. 7 discloses an oscillator and drive circuit which is an alternative to that of FIGS. 5 and 6 and which permits the coil of driver 20 to function both as a drive coil, as previously described, as well as a detector. This eliminates the need for accelerometer 30. Drive circuit 700 on FIG. 7 comprises the pulse generator 701, a multiplexer 703, driver 20, sample and hold circuit 705 and timing circuit 706. The operational position of multiplexer 703 is controlled over path 711 by timing circuit 706. This circuit controllably permits input 712 of driver coil 20 either to be connected over path 709 to the output of amplifier 702 or over path 710 to the input of amplifier 704. Sample and hold 705 includes a circuit which operates under control of timing, circuitry 706 and which receives " input signals from the output of amplifier 704. The sample and hold circuit periodically sends control signals over path 707 to pulse generator 701 to cause it to generate a pulse of a predetermined amplitude and width. This generated pulse is applied over path 708, amplified by amplifier 702 and applied over path 709 to drive coil 20 when multiplexer 703 is in the position illustrated on FIG. 1. This pulse causes the pipe to which drive coil 20 is attached to move. Subsequent to the generation of this pulse, the sample and hold circuit transmits a signal over path 711 to cause the multiplexer to switch to its operational position in which drive coil 20 is connected to path 710. In this position, the movement of the pipe resulting from the application of the first drive pulse to coil 20 induces a voltage in coil 20 which is now operating as a signal detector. This detected signal is applied over path 710, amplified by amplifier 704 and applied over path 714 to sample and hold circuit 705. The circuit analyzes the characteristics of the received signal to determine whether the pipe is vibrating at the correct amplitude and frequency. If the pipe's vibration amplitude and frequency are correct, sample and hold circuit 705 causes the operational position of the multiplexer to revert to that shown on FIG. 1 and transmits a control signal over path 707 to pulse generator 701 so that it now generates a second pulse having the same characteristics as the first generated pulse. This second pulse is applied via amplifier 702 and multiplexer 703 to drive coil 20 to continue the oscillation of pipe 10 at the correct frequency and amplitude. Alternatively, if the sample and hold circuit 705 determines from the signal on path 714 that the pipe is not vibrating at the correct amplitude and frequency, it alters the characteristics of the signal it applies to path 707 to command pulse generator 701 to alter the characteristics of its generated pulse that is applied to drive coil 20. This causes pipe 10 to be vibrated at the correct frequency and amplitude. It may be seen from the above that the circuit of FIG. 7 is advantageous in that it eliminates the need for the provision of accelerometer 30 as a separate feedback element for the drive circuitry of driver 20. This is done by using the driver 20 as a dual functional element wherein at one period of time it is connected by multiplexer 703 to a drive signal to vibrate the pipe 10 at the required amplitude and frequency. At another period of time, driver 20 is used as a signal detector when the operational position of the multiplexer switches so that the coil of driver 20 is connected to circuitry including a sample and hold circuit and its signal processor which controls the amplitude and frequency of the drive signals to driver 20. The preceding has shown how the circuitry of FIG. 5 or FIG. 6 or FIG. 7 can be used to generate and apply drive signals to driver 20. If desired, the apparatus and circuitry shown in U.S. Patent No. 5,009,109 of April 23, 1991, to Paul Kalotay et al. could be used to generate and apply a non- continuous drive signal to driver 20. While a specific embodiment of this invention has been disclosed, it is expected that those skilled in the art can and will design alternate embodiments of this invention that fall within the scope of the appended claims.

Claims: I claim: 1. A method of determining information including the mass flow rate of material flowing through a pipe section 10, said method comprising the steps of: positioning a first motion detector 32 at a first location comprising a zero flow node location of a harmonic of the natural frequency of vibration of said pipe section, positioning a vibration driver 20 at a second location of said pipe section, operating said driver to oscillate said pipe section at said harmonic frequency, and determining the mass flow rate of said material flowing through said pipe section by measuring with said motion detector the amplitude of a transverse deflection of said first location of said pipe section in a direction perpendicular to the longitudinal axis of said pipe section. 2. The method of claim 1 wherein said pipe section is essentially straight and devoid of curves. 3. The method of claim 1 wherein said pipe section has an inner cross sectional area that is equal to the inner area of a supply pipe and an exit pipe connected to ends of said pipe section. 4. The method of claim 1 wherein said method further comprises the steps of: clamping ends of said pipe section to a support structure 12,14, and oscillating only the portion of said pipe section between said ends at said harmonic frequency. 5. The method of claim 1 wherein said step of determining comprises the step of: measuring with said motion detector 32 the amplitude of said transverse deflection of said first pipe section location caused jointly by said material flow and said oscillation of said pipe section, applying an output signal of said detector representing said measured amplitude to measuring apparatus, and operating said measuring apparatus 540,541 for determining the mass flow rate of said material in said pipe section. 6. The method of claim 1 wherein said method further comprises the step of: affixing a counter weight 40 to a third location on said pipe section an opposite side of said first location with respect to the location to which said driver is attached. 7. The method of claim 1 wherein said step of oscillating said pipe section comprises the steps of: positioning a second motion detector 30 at said second location of said pipe section, operating said second motion detector 30 to detect the amplitude of oscillation of said second pipe section location, applying an output signal from said second motion detector to control circuitry 504,507,508 to generate a drive signal 509 of a substantially constant amplitude and at said harmonic of the natural frequency of vibration of said pipe section, and applying said constant amplitude signal to said driver so that said driver oscillates said pipe section at a substantially constant amplitude and at said harmonic of the natural frequency of vibration of said pipe section. 8. The method of claim 1 wherein said method further comprises the steps of: positioning a third motion detector 34 to detect noise vibrations of the environment external to said pipe section, applying an output signal of said third detector to subtraction circuitry 536, applying an output of said first motion detector to said subtraction circuitry, said subtraction circuitry being effective to remove external environment noise signals in said output signal of said first motion detector to provide a filtered signal representing the amplitude of the motion of said pipe section location caused jointly by said oscillations and by the Coriolis motion of said pipe section due to the flow of material in said oscillating pipe section. 9. The method of claim 1 wherein said harmonic frequency comprises the second harmonic of the natural frequency of vibration of said pipe section. 10. The method of claim 1 wherein said pipe section is essentially straight and devoid of curves; wherein said pipe section has an inner cross sectional area that is equal to the inner area of a supply pipe and an exit pipe connected to ends of said pipe section; wherein said method further comprises the steps of: clamping ends of said section of said pipe to a support structure 12,14, oscillating only said section of said pipe section between said ends at said harmonic frequency of vibration; wherein said step of determining comprises the step of: measuring with said motion detector 32 the amplitude of said transverse deflection of said first pipe section location caused by said material flow and said oscillation, applying an output signal 511 of said first motion detector representing said measured amplitude to measuring apparatus 540,543, operating said measuring apparatus for determining the mass flow rate of said material in said pipe in said pipe section; wherein said method further comprises the step of: affixing a counter weight 40 to a third location on said pipe section an opposite side of said first location with respect to the location to which said driver is attached; wherein said step of oscillating said pipe section comprises the steps of: positioning a second motion detector 30 at said second location of said pipe section, operating said second motion detector to detect the amplitude of oscillation of said second location of said pipe section, applying an output signal 502 from said second motion detector to control circuitry to generate a drive signal of a substantially constant amplitude and at said harmonic of the natural frequency of vibration of said pipe section, and applying said constant amplitude signal to said driver so that said driver oscillates said pipe section at a substantially constant amplitude and at said harmonic of the natural frequency, wherein said method further comprises the steps of: positioning a third motion detector 34 to detect noise vibrations of the environment external to said pipe section, applying an output signal 531 of said third detector to subtraction circuitry 536, applying an output of said first motion detector to said subtraction circuitry, said subtraction circuitry being effective to remove any external environment noise signal in said output signal of said first detector to provide a filtered signal representing the amplitude of the motion of said first location of said pipe section caused jointly by said oscillations and by the Coriolis motion of said pipe section due to the flow of material in said oscillating pipe section; and wherein said harmonic frequency comprises the second harmonic of the natural frequency of vibration of said pipe section. 11. The method of claim 1 wherein said vibration driver 20 includes a magnetostrictive transducer 300 to oscillate said pipe section, and said step of operating said driver includes: applying a drive current to said magnetostrictive transducer to force the magnetostrictive element in said transducer to elongate and return to normal length according to the frequency of said drive current; and adjusting said frequency of said drive current to operate said driver to drive said pipe section at said harmonic frequency. 12. The method of claim 11 wherein said method further comprises the steps of: periodically stopping the application of said drive current to said- magnetostrictive transducer; measuring the electromotive force produced by the changes in length of said magnetostrictive element from the force of the oscillation of said pipe section to determine the frequency of oscillation of said pipe section; and applying a signal resulting from said measured electromotive force to control circuitry for operating said magnetostrictive transducer at said harmonic mode of the natural frequency of vibration of said pipe section. 13. The method of claim 1 wherein said vibration driver includes an electromagnetic coil 306 supported on an external support for oscillating said pipe section; and wherein said operation of said vibration driver includes a feedback coil attachment 401 supported on an external support. 14. A method of determining the mass flow rate of material flowing through a pipe, said method comprising the steps of: clamping a section of said pipe at a first 12 and a second pipe 14 location spaced apart from each other to inhibit transverse motion of said pipe section at said locations, affixing a first motion detector 32 to said pipe section at a third location between said first and second locations, said third location comprising a zero flow vibration node for a harmonic of the natural frequency of vibration of said pipe section, affixing a vibration driver 20 to said pipe at a fourth location between said, third location and said first location, said fourth location not comprising a vibration node of said pipe section at said harmonic frequency, operating said driver to oscillate said pipe section at said harmonic frequency, and determining the mass flow rate of said material through said pipe section by measuring with said motion detector the amplitude of the transverse deflection of said third location of said pipe section in a direction perpendicular to the longitudinal axis of said pipe section. 15. The method of claim 14 wherein said pipe section is essentially straight and devoid of curves. 16. The method of claim 14 wherein said detector and said driver are attached only to said pipe section and are free from attachment to a non-movable object. 17. The method of claim 14 wherein said pipe section has an inner cross sectional area that is equal to the inner area of a material supply pipe and a material exit pipe connected to ends of said pipe section. 18. The method of claim 14 wherein said step of determining comprises the step of: measuring with said motion detector the amplitude of a transverse deflection of said third pipe section location caused jointly by said material flow and said oscillation, applying an output signal 511 of said first motion detector representing said measured amplitude to measuring apparatus, and operating said measuring apparatus 540,541 for determining the mass flow rate of said material in said pipe section in said pipe section. 19. The method of claim 14 wherein said method further comprises the step of: affixing a counter weight 40 to a fifth location on said pipe section on an opposite side of said third location with respect to the said fourth location to which said driver is attached. 20. A method of determining the mass flow rate of material flowing through a pipe, said method comprising the steps of: affixing a first motion detector 32 to said pipe at a first location comprising a zero flow vibration node for a harmonic of the natural frequency of vibration of said pipe, affixing a vibration driver 20 to said pipe at a second pipe location, operating said driver to oscillate said pipe section at said harmonic frequency, and determining the mass flow rate of said material through said pipe section by measuring with said first motion detector the amplitude of the transverse deflection of said first location of said pipe caused jointly by the oscillation of said pipe and the flow of material through said pipe. 21. The method of claim 20 wherein said first motion detector 32 and said driver 20 are attached only to said pipe and are free from attachment to a non-movable object. 22. The method of claim 20 wherein said step of determining comprises the step of: measuring with said first motion detector the amplitude of a transverse deflection of said first pipe location caused by said material flow and said oscillation, applying an output signal 511 of said first motion detector 32 representing said measured amplitude to measuring apparatus, and operating said measuring apparatus 540,541 for determining the mass flow rate of said material in said pipe in said pipe. 23. The method of claim 20 wherein said method further comprises the step of: affixing a counter weight 30 to a third pipe location at an anti-node on an opposite side of said first location with respect to the location to which said driver is attached. 24. A flow meter for measuring the mass flow rate of material flowing through a pipe section; said flow meter comprising: a motion detecting sensor means 32 affixed to a first pipe section location for detecting transverse deflections of said pipe section; a vibrating means 20 affixed to a second location on said pipe section; means 30,503,507,508 for operating saidvibrating means 20 to vibrate said pipe section at a harmonic of the natural frequency of vibration of said pipe section; and means 540,541 for determining the mass flow rate of said material flowing through said pipe section from the amplitude of a transverse deflection of said pipe section at said first location as detected by said motion detecting means. 25. The flow meter of claim 24 wherein said means for vibrating said pipe section includes a second sensor 30 mounted adjacent said vibrating means and a feed back circuit 503,506,508 connected between said sensor and said vibrating means to control said harmonic frequency of vibration. 26. The flow meter of claim 24 wherein said means 312 for affixing said vibrating means to said pipe section include means for clamping said vibrating means directly onto said pipe section without external supports. 27. The flow meter of claim 24 wherein said means for vibrating said pipe section include a magnetostrictive driver (FIG. 3) for oscillating said pipe section at a frequency determined by the frequency of a drive current applied to said magnetostrictive driver. 28. The flow meter of claim 24 wherein said magnetostrictive driver includes: a cylindrical nickel alloy rod 302; a solenoid coil 306 surrounding said rod to apply a driving electromagnetic field to said rod to cause said rod to elongate when said electromagnetic field is applied to it and to return to normal length when said electromagnetic field is removed; means 508 for providing an alternating current to said coil; a tubular permanent magnet 304 surrounding said coil to provide a magnetic bias field to said coil and rod; shunts 310,308 at each end of said magnet to complete a magnetic circuit; resilient means 322 for providing pre-stress on said rod to improve the power efficiency of said driver; and a mass 320 for providing an opposing force to said driver. 29. The flow meter of claim 24 wherein said vibrating means further comprises means 30 for sensing the frequency of oscillation of said pipe section. 30. The flow meter of claim 24 wherein said motion detecting sensor means include an accelerometer. 31. The flow meter of claim 25 wherein said meter includes a third sensor 34 mounted on an external support for measuring extraneous noise, and means 536 for subtracting said extraneous noise from an output signal of said motion detector sensor means. 32. The flow meter of claim 24 wherein said flow meter further includes support means 12,14 attached to said section of pipe to isolate said section of pipe from extraneous vibrations. 33. The flow meter of claim 24 wherein said flow meter further includes a separate section of pipe (FIG. 1) with said driver and said motion sensor being affixed thereto, and means for mounting said separate section of pipe to an existing pipe. 34. The flow meter of claim 24 wherein said flow meter further comprises counterweight means 30 affixed to said pipe section in a location to balance forces on said pipe section resulting from said vibration caused by said vibrating means. 35. The flow meter of claim 24 wherein said flow meter further comprises a plurality of said vibrating means affixed to said pipe section for vibrating said pipe section. 36. Apparatus for determining the mass flow rate of material flowing through a pipe, said apparatus comprising: means 12,14 for clamping a section of said pipe at a first and a second pipe location spaced apart from each other to inhibit transverse motion of said pipe section at said locations, a first motion detector 32 affixed to said pipe section at a third location between said first and second locations, said third location comprising a zero flow vibration node for a harmonic of the natural frequency of vibration of said pipe section, a vibration driver 20 affixed to said pipe at a fourth location between said third location and said first location, said fourth location not comprising a vibration node of said pipe section at said harmonic frequency, means 508 for operating said driver to oscillate said pipe section at said harmonic frequency, and means 540,541 for determining the mass flow rate of said material through said pipe section by measuring with said motion detector the amplitude of the transverse deflection of said third location of said pipe section in a direction perpendicular to the longitudinal axis of said pipe section. 37. The apparatus of claim 36 wherein said pipe section is essentially straight and devoid of curves. 38. The apparatus of claim 36 wherein said detector and said driver are attached only to said pipe section and are free from attachment to a non- movable object. 39. The apparatus of claim 36 wherein said pipe section has an inner cross sectional area that is equal to the inner area of a material supply pipe and a material exit pipe connected to ends of- said pipe section. 40. The apparatus of claim 36 wherein said means for determining comprises: means for measuring with said motion detector 32 the amplitude of a transverse deflection of said third pipe section location caused jointly by said material flow and said oscillation, means 511 for applying an output signal of said detector representing said measured amplitude to measuring apparatus, and means 540,541 for operating said measuring apparatus for determining the mass flow rate of said material in said pipe section in said pipe section. 41. The method of claim 36 wherein said method further comprises the step of: affixing a counter weight 40 to a fifth location on said pipe section on an opposite side of said third location with respect to the said fourth location to which said driver is attached. 42. Apparatus for determining the mass flow rate of material flowing through a pipe, said apparatus comprising: a motion detector 32 affixed to said pipe at a first location comprising a zero flow vibration node for a harmonic of the natural frequency of vibration of said pipe, a vibration driver 20 affixed to said pipe at a second pipe location, means 508 for operating said driver to oscillate said pipe section at said harmonic frequency, and means 540,541 for determining the mass flow rate of said material through said pipe section by measuring with said motion detector the amplitude of the transverse deflection of said first location of said pipe caused jointly by the oscillation of said pipe and the flow of material through said pipe. 43. The apparatus of claim 42 wherein said detector and said driver are attached only to said pipe and are free from attachment to a non-movable object. 44. The apparatus of claim 42 wherein said means for determining comprises: means for measuring with said motion detector the amplitude of a transverse deflection of said first pipe location caused by said material flow and said oscillation, means 511 for applying an output signal of said motion detector representing said measured amplitude to measuring apparatus, and means . 524 for operating said measuring apparatus 540,541 for determining the mass flow rate of said material in said pipe in said pipe. 45. The apparatus of claim 42 wherein said apparatus further comprises: a counter weight 40 affixed to a third pipe location at an anti-node on an opposite side of said location with respect to the location to which said driver is attached.

Inventors: KALOTAY PAUL ZOLTAN, KALOTAY, PAUL, ZOLTAN
Applicants: MICRO MOTION INC, MICRO MOTION, INC.
Application year: 1992
Main classification: G01F1
IPC codes: G01F1