Method for operating a resonance-measuring system and respective resonance system

Abstract

A method for operating a resonant measurement system has at least one: adjustment device, electric actuation device, electromagnetic vibration generator, vibrating element, and vibration recorder. The adjustment device generates an output signal to trigger the electric actuation device, the electric actuation device provides an electric excitation signal to the electromagnetic drive, the electromagnetic drive excites the vibrating element to the same vibration in at least one normal mode, and the excited vibration is sensed by the vibration recorder and is output as an output signal. To approach, maintain and readjust a resonant point as an operating point of the resonant measurement system, the phase difference between the output signal of the vibration recorder and the adjustment device output signal is acquired, an adjustment deviation is calculated from a predefined phase difference and the acquired phase difference, and the adjustment deviation provided to the adjustment device as an input signal.

Claims

1. Method for operating a resonance-measuring system having at least one controller, at least one electric setting device, at least one electromagnetic drive with a drive coil, at least one oscillation element and at least one oscillation sensor, comprising the steps of: using said at least one controller to generate a controller output signal u.sub.1 for controlling the electric setting device, wherein the at least one electric setting device provides a voltage u.sub.s as an electric excitation signal u.sub.2 for exciting the electromagnetic drive, and wherein the voltage u.sub.2 is applied as a terminal voltage of the drive coil of the electromagnetic drive, using the electric setting device to provide an electric excitation signal u.sub.2 for exciting the electromagnetic drive, using the electromagnetic drive to excite the oscillation element into oscillation in at least one natural mode, detecting the excited oscillation of the oscillation element with the oscillation sensor and outputting the detected excited oscillation as at least one output signal y based on the excited oscillation detected, using an electronic circuit for determining a controller-oscillation-sensor-phase-difference between the output signal of the oscillation sensor and the controller output signal u.sub.1 in a control loop on the basis of the output signal and a measured controller output signal, using a digital signal processor for calculating a control deviation e using a predetermined phase difference and the determined controller-oscillation-sensor-phase-difference, separately determining a controller-drive-phase-difference on the basis of the measured controller output signal u_1 and a measured current in the coil of the electromagnetic drive, and using the controller-drive-phase-difference (i.sub.s, u.sub.1) as the predetermined phase difference, and providing the control deviation to the controller as an input signal of a control loop for ongoing control of the electric setting device so to adjust excitation of the oscillation element into oscillation close to the resonance point of the resonance-measuring system based on the controller-oscillation-sensor-phase difference.

2. Method according to claim 1, wherein the predetermined phase difference is chosen such that the oscillation element is excited to oscillation in at least one natural mode in resonance or near a point of resonance.

3. Method according to claim 1, wherein the determined controller-drive-phase-difference is filtered with a low-pass filter having a time constant in a seconds range.

4. Method according to claim 3, wherein a harmonic base signal is generated by the controller as the controller output signal u.sub.1 for determining at least one of the controller-oscillation-sensor-phase-difference and the controller-drive-phase-difference (i.sub.S, u.sub.1), wherein each phase difference is determined using demodulation of each signal y, i.sub.s of interest with the harmonic base signal and a further harmonic base signal, orthogonal to the first harmonic base signal, provided by the controller.

5. Method according to claim 1, wherein one of mass flow rate, density and fill level is determined from an output of the system.

6. Resonance-measuring system, comprising: an electromagnetic drive, at least one controller, at least one electric setting device, at least one oscillation element, and at least one oscillation sensor, wherein the controller is configured for generating a controller output signal for controlling the electric setting device, wherein the electric setting device is adapted to provide an electric excitation signal for exciting the electromagnetic drive, wherein the electromagnetic drive is configured for exciting the oscillation element into oscillation in at least one natural mode, wherein the oscillation sensor is configured for detecting excited oscillation of the oscillation element and for outputting at least one output signal, and wherein a control loop is formed on the basis of the output signal and the controller output signal in such a manner that a controller-oscillation-sensor-phase-difference between the output signal of the oscillation sensor and the controller output signal determined on the basis of the controller output signal and the current in the coil of the electromagnetic drive and controls the electric setting device so to adjust excitation of the oscillation element into oscillation close to the resonance point of the resonance-measuring system.

7. Resonance-measuring system according to claim 6, wherein the electric setting device is a voltage-controlled voltage transformer.

8. Resonance-measuring system according to claim 6, wherein the system is a Coriolis mass flowmeter.

9. Method for operating a resonance-measuring system having at least one controller, at least one electric setting device, at least one electromagnetic drive with a drive coil, at least one oscillation element and at least one oscillation sensor, comprising the steps of: using said at least one controller to generate a controller output signal for controlling the electric setting device, using the electric setting device to provide an electric excitation signal for exciting the drive coil of the electromagnetic drive, wherein the electric setting device provides a voltage us as an electric excitation signal for exciting the electromagnetic drive, and wherein the voltage us is applied as a terminal voltage of the drive coil of the electromagnetic drive, using the electromagnetic drive to excite the oscillation element into oscillation in at least one natural mode, detecting the excited oscillation of the oscillation element with the oscillation sensor and outputting the detected excited oscillation as at least one output signal y based on the excited oscillation detected, using an electronic circuit for determining a controller-oscillation-sensor-phase-difference between the output signal of the oscillation sensor and the controller output signal u.sub.1 in a control loop on the basis of the output signal and a measured controller output signal, using a digital signal processor for calculating a control deviation e using a predetermined phase difference and the determined controller-oscillation-sensor-phase-difference, determining a controller-drive-phase-difference between a state variable of the electromagnetic drive and the controller output signal on the basis of the measured controller output signal and a measured current in the coil of the electromagnetic drive, and separately calculating the predetermined phase difference .sub.S1 using the determined controller-drive-phase-difference and an additional predetermined phase difference .sub.S2, using the current of the drive coil as the state variable of the electromagnetic drive, providing the control deviation to the controller as an input signal of a control loop for ongoing control of the electric setting device so to adjust excitation of the oscillation element into oscillation close to the resonance point of the resonance-measuring system.

10. Method according to claim 9, wherein the determined controller-drive-phase-difference is filtered with a low-pass filter having a time constant in a seconds range.

11. Method according to claim 9, wherein a harmonic base signal is generated by the controller as the controller output signal for determining at least one of the controller-oscillation-sensor-phase-difference and the controller-drive-phase-difference, wherein each phase difference is determined using demodulation of each signal, is of interest with the harmonic base signal and a further harmonic base signal, orthogonal to the first harmonic base signal, provided by the controller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows the structure of a resonance-measuring system in the form of a Coriolis mass flowmeter as it is known from the prior art as it could be used for the method according to the invention,

(2) FIG. 2 is an equivalent circuit diagram of a coil contained in an electromagnetic drive with an electric setting device,

(3) FIG. 3 is a block diagram of the method according to the invention for operating a resonance-measuring system,

(4) FIG. 4 is a block diagram of a further embodiment of the method according to the invention for operating a resonance-measuring system,

(5) FIG. 5 is a block diagram of another further developed embodiment of the method according to the invention for operating a resonance-measuring system and

(6) FIG. 6 is a block diagram of a final further developed embodiment of the method according to the invention for operating a resonance-measuring system with a view of the components.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a resonance-measuring system 1 in the form of a Coriolis mass flowmeter, wherein the resonance-measuring system 1 has a controller 2 implemented in a digital signal processor, an electronic setting device 3, and an electromagnetic drive 4 as oscillation generator.

(8) The electromagnetic drive 4 has the function of exciting an oscillation element 5, presently a measuring tube flowable with medium, to oscillation in a natural mode. Depending on the type of natural mode, only one single electromagnetic drive 4 is necessary for this, however, if higher modes are to be excited, two or more electromagnetic drives 4 may be necessary.

(9) In FIG. 1, the resonance-measuring system 1 in the form of a Coriolis mass flowmeter is shown in two parts. The Coriolis mass flowmeter forming one unit ends at one half on the right side of the drawing and begins with the other half on the left side of the drawing for a more clear representation. It can be seen there that the resonance-measuring system 1 also has oscillation sensors 6 that emit an output signal y, presently in the form of a velocity signal, which provides information about the velocity movement in the measuring tube, i.e., the oscillation element 5. The controller 2 generates a controller output signal u.sub.1 for controlling the electric setting device 3 and the electric setting device 3 subsequently generates an electric excitation signal u.sub.2 for exciting the electromagnetic drive 4. Several transmission elements connect to the oscillation sensor 6, which are essentially used for signal processing, such as, for example, adaptation electronics 7a consisting of amplifiers, a hardware multiplexer 7b for implementing different switchable measuring channels, a further adaptation electronics 7c and an analog/digital converter 7d, which returns the analog measured signals back to the controller 2 in the form of digital signals.

(10) In the prior art, the control loop implemented in this manner forms a phase control loop and is based on the impression of a current is in a coil 8 of the electromagnetic drive 4. This concept is shown again in FIG. 2 for clarification; the electromagnetic drive 4 has a drive coil 8 here, which has a coil inductivity L.sub.S, an ohmic coil resistance R.sub.S, and an induced voltage source u.sub.is proportional to the velocity (u.sub.S=i.sub.SR.sub.S+L*di.sub.S/dt+k*dv/dt) in the equivalent circuit diagram according to FIG. 2. The electric setting device 3 operates with a voltage-controlled current source 9, which receives quantized voltage signals from a digital/analog converter 10, which leads to erratic changes of the coil current is at the outlet of the voltage-controlled current source 9. This current impression inevitably leads to even more turbulent changes of the terminal voltage us at the coil 8, which also leads to a noisy current signal i.sub.s due to different influences.

(11) In the electromagnetic drive 4, which, as shown in FIG. 2, has a coil 8, the coil current i.sub.S is of particular importance, because the coil current i.sub.S is that state variable of the electromagnetic drive 4 that is proportional to the force of the electromagnetic drive 4 on the oscillation element 5. In the case of a Coriolis mass flowmeter as resonance-measuring system 1, the phase difference between the force acting on the oscillation element 5 and thus also between the coil current i.sub.S and the detected velocity y of the measuring tube movement is zero where resonance occurs. The implementation of a phase control at the resonance working point using the coil current i.sub.S as input variable and state variable of the electromagnetic drive and using the velocity signal as output signal y of the oscillation sensor 6 is problematic: the requirements on the used electric components is, then, very high, since broadband components having low phase deviations in the working point have to be used, which makes this solution expensive overall.

(12) The method for operating a resonance-measuring system 1 according to the invention is shown in FIG. 1, namely is shown in the form of a block diagram. The controller 2 controls the electric setting device 3 via the controller output signal u.sub.1, wherein the electric setting device 3 controls the electromagnetic drive 4 using the output of electric excitation signals u.sub.2 that deflect the oscillation element 5 as oscillation generator, which is present here as a measuring tube of a Coriolis mass flowmeter. The electromagnetic drive 4 consists of a schematically-illustrated coil 8 with a permanent magnetic as its core, wherein the (not shown) permanent magnet carries out a stroke movement when the coil 8 is fed a current and, in this manner, can excite the oscillation element 5 to oscillation. The oscillation of the oscillation element 5 is detected by the oscillation sensor 6, which, in the present case, also has a permanent magnet and a coil, wherein the voltage induced in the coil 8 is used for evaluating the change of position of the oscillation element 5. The velocity signal is presently the output signal y of the oscillation sensor 6.

(13) The method according to the invention provides that initially the controller-oscillation-sensor-phase-difference (y, u.sub.1) is detected between the output signal y of the oscillation sensor 6 and the controller output signal u.sub.1 and a control deviation is calculated using a predetermined phase difference .sub.S1 and this controller-oscillation-sensor-phase difference (y, u.sub.1), wherein this control deviation e is provided to the controller 2 as an input signal. Thus, a control loop is implemented that controls based on the controller-oscillation-sensor-phase-difference (y, u.sub.1) and not based on the phase difference that is actually decisive for a control based on the resonance point of the resonance-measuring system, presently, namely, the phase difference between the coil current i.sub.S and the velocity signal y at the outlet of the oscillation sensor 6. Thus, an error is accepted, namely the unconsidered phase shift, which is caused by the electric setting device 3. This phase shift is incorrectlybut deliberatelyadded to the core of the resonance-measuring system 1, namely the electromagnetic drive 4, the oscillation element 5 and the oscillation sensor 6. The advantage of the method according to the invention is that a very fast control can be implemented with a working point that is quite close to the resonance point of a resonance-measuring system 1 using the control based on the controller-oscillation-sensor-phase difference (y, u.sub.1) with comparably non-noisy signals, so that, with a small limitation in resonance phasing, a downright fast control can be implemented, a control that additionally no longer requires the use of components with a large band width and requires only a very small phase shift of the electric setting device in the working frequency range.

(14) In the simplest case, the predetermined phase difference .sub.S1 is set at the value that would result as phasing or phase difference between the controller output signal u.sub.1 and the output signal y of the oscillation sensor 6 if the electric setting device 3 caused practically no phase shift and the resonance case were set. In the case shown of the Coriolis mass flowmeter, this corresponds to setting the predetermined phase difference .sub.S1 to zero; in this form, the oscillation element 5 is excited to oscillation in a natural form in resonance or near the resonance point.

(15) A further embodiment of the above-described method is shown in FIG. 4, in which a controller-drive-phase-difference (i.sub.S, u.sub.1) between the state variable i.sub.S of the electromagnetic drive 4 and the controller output signal u.sub.1 is determined, wherein the controller-drive-phase-difference (i.sub.S, u.sub.1) is then used as predetermined phase difference .sub.S1. The error accepted above in the phase control is compensated again due to this measure.

(16) In the further development of the method shown in FIG. 5, the controller-drive-phase-difference (i.sub.S, u.sub.1) is also initially additionally determined between the state variable i.sub.S of the electromagnetic drive 4 and the controller output signal u.sub.1, wherein, then, the predetermined phase difference .sub.S1 is calculated using the controller-drive-phase difference (i.sub.S, i.sub.1) and a further predetermined phase difference .sub.S1, which allows other phase specifications and also other operation modes, for example a phase-selective excitation of the Coriolis mass flowmeter at a phase specification of .sub.S2=+/45.

(17) In both variations of the method shown in FIGS. 4 and 5, the current detected in the drive coil 8 employed there is used as state variable i.sub.S of the electromagnetic drive 4.

(18) The method described as yet allows the use of a voltage-controlled current source as electric setting device 3, as well as a voltage-controlled current source that meets only a few high requirements, such as those requirements known from the prior art for phase control that are directed toward the immediate input and output variables of the resonance section. This allows for the use of economical standard components.

(19) Of particular advantage is that the method can be used when the electric setting device 3 provides a voltage u.sub.S as electric excitation signal u.sub.2 for exciting the electromagnetic drive 4, which is the case in FIGS. 3 to 6, here the voltage u.sub.S is applied as supply voltage of the drive coil 8 of the electromagnetic drive 4. This also makes sense for the solitaryfastphase control based on the controller-oscillation-sensor-phase-difference (y, u.sub.1) between the output signal y of the oscillation sensor 6 and the controller output signal u.sub.1, and makes sense for an additional correction of the predetermined phase difference .sub.S1 by determining the controller-drive-phase-difference (i.sub.S, u.sub.1) between the state variable i.sub.S of the electromagnetic drive 4 and the controller output signal u.sub.1. In any case, the current impression and the consequent and above-described interference are avoided.

(20) FIG. 6 again shows a resonance-measuring system 1 in greater detail in the form of a Coriolis mass flowmeter, wherein the resonance-measuring system 1 has a controller 2a, 2b implemented in a digital signal processor (DSP), an electric setting device 3 with a digital/analog converter 3a and a voltage-controlled voltage source 3b as power unit. As in the above examples, the electromagnetic drive 4 has a coil 8 as oscillation generator.

(21) The fast control loop is implemented in the lower signal path, which is based on the controller-oscillation-sensor-phase-difference (y, u.sub.1) between the output signal y of the oscillation sensor 6 and the controller output signal u.sub.1. Theslowercalculation of the correction value for the phase difference is implemented in the upper signal path, which is based on the controller-drive-phase-difference (i.sub.S, u.sub.1) between the state variable i.sub.S of the electromagnetic drive 4 and the controller output signal u.sub.1. The detected current signal as well as the detected velocity signal y are digitized by an analog/digital converter 11, 12 and fed to the DSP. Demodulators 13, 14 dismantle the measuring variables i.sub.S,y with the help of orthogonal base signals in signal components, which allow for the determination of the phasing of the signals in respect to the base signal u.sub.1, wherein the controller-drive-phase-difference (i.sub.S, u.sub.1) is also filtered over a low pass filter 15 and wherein this low pass filter has a time constant of about two seconds.

(22) The implementation of the electric setting device 3 as voltage-controlled voltage converters has the further unexpected advantage that the low output resistance of the voltage-controlled voltage converter acts as a short-circuit in view of the drive coil 8 and thus a damping of the oscillation of the measuring tube is achieved depending on the velocity of the measuring tube. Thus, the installation of short-circuit loops in the electromagnetic drive 4 for the purpose of damping of the generally weakly damped system can be omitted.