JPH0575338B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an electromagnetic flowmeter that applies a magnetic field to a fluid to be measured and measures its flow rate, and particularly relates to an excitation method thereof and a signal processing method associated therewith. This invention relates to an improved electromagnetic flowmeter.

<Prior Art> Industrial electromagnetic flowmeters have conventionally adopted a commercial frequency excitation method using a commercial power supply. The commercial frequency excitation method has (a) fast response speed and low cost. (b) It has the advantage of being less susceptible to the effects of low-frequency random noise (hereinafter referred to as flow noise) that increases with flow velocity that occurs in slurry fluids and low conductivity fluids, but However, it has the disadvantage that the zero point will fluctuate if left unattended for a long period of time, for example, about one day.

For this reason, a low frequency excitation method that excites at a low frequency of 1/2 of the commercial frequency or lower has been adopted. As is well known, the low frequency excitation method has the advantage of providing an electromagnetic flowmeter with a stable zero point. However, since the excitation frequency is low, it is close to the frequency of flow noise, and is therefore susceptible to the influence of flow noise, and this influence becomes particularly noticeable as the flow velocity increases. Furthermore, when damping is applied to reduce the influence of flow noise, the response becomes slow.

Therefore, as proposed in Japanese Patent Application No. 60-197168 (title of invention: electromagnetic flowmeter), a high-frequency excitation current component with a commercial frequency or higher frequency and a low-frequency excitation current component with a lower frequency are proposed. A two-frequency excitation method has been proposed in which a two-frequency magnetic field is formed by simultaneously causing a current component to flow through an excitation coil.

<Problems to be solved by the invention> However, although this proposal has the advantage of having a stable zero point, strong resistance to flow noise, and good response, it requires a high-pass filter with a large time constant on the high frequency side. Yes, there is a low-pass filter with a large time constant on the low frequency side, so if you try to calculate a normal flow rate output when the power is turned on or when the normal state returns after noise has been superimposed, you will have to There is a problem in that it is difficult to reach a state in which a normal flow rate output can be produced due to the large time constant.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides excitation means for supplying magnetic fields having two different frequencies, a first frequency and a second frequency lower than the first frequency;
A first demodulation calculation means for discriminating and outputting a signal voltage excited by the excitation means and generated corresponding to the flow rate based on a first frequency; A high-pass filter calculation means for filtering, a second demodulation calculation means for discriminating and demodulating the signal voltage based on a second frequency, and a low-pass filter for low-pass filtering the output of the second demodulation calculation means with a large low-frequency time constant. a filter calculation means; a synthesis calculation means for calculating a flow rate output by algebraically synthesizing each output of the high-pass filter calculation means and the low-pass filter calculation means; and a synthesis calculation means for calculating a normal flow rate output corresponding to a signal voltage. a judgment means for judging whether or not the calculation state is suitable for the calculation, and a judgment means for determining whether the calculation state is suitable for the calculation, and setting the high-frequency time constant and the low-pass time constant to be initially small and then set to be large when in the calculation state based on the result of this judgment means. A time constant changing means is provided.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention.

10 is a conduit for a detector of an electromagnetic flowmeter, and an insulating lining is provided on the inner surface of the conduit. 11
a and 11b are electrodes for detecting a signal voltage. Reference numeral 12 denotes an excitation coil, and a magnetic field generated thereby is applied to the fluid to be measured. An excitation current I _f is supplied to the excitation coil 12 from an excitation circuit 13 .

The excitation circuit 13 is configured as follows. The reference voltage E ₁ is applied to the non-inverting input (+) of the amplifier Q ₁ , the output of which is connected to the base of the transistor Q ₂ . The emitter of the transistor _Q2 is connected to the common COM via a resistor R _f and also to the inverting input terminal (-) of the amplifier _Q1 . An excitation voltage E _S is applied between the common COM and the collector of the transistor Q ₂ through the series circuit of switches SW ₂ and SW ₃ and the switch SW ₄ connected in parallel to this.
Applied via SW ₅ series circuit. The excitation coil 12 is connected to the connection point of switches SW ₂ and SW ₃ and the switch
Connected to the connection points of SW ₄ and SW ₅ , respectively. Timing signals S ₂ , S ₃ , S ₄ , and S ₅ are switches, respectively.
Controls the opening and closing of SW ₂ , SW ₃ , SW ₄ , and SW ₅ .

On the other hand, the signal voltage is detected by the electrodes 11a and 11b and output to the preamplifier 14. Preamplifier 1
4, the common mode voltage is removed and the impedance is converted, and the resultant signal is output to the output terminal 15.

The output of the preamplifier 14 at the output terminal 15 is converted into a digital signal by an analog/digital converter (A/D _L ) 16 and an analog/digital converter (A/D _H ) 17, respectively, and is randomly transmitted via a bus 18. The data is stored in access memory (RAM) 19. A read-only memory (ROM) 20 stores predetermined calculation programs and initial data, and is processed under the control of a processor (CPU) 21.
The calculation is performed according to the calculation procedure stored in the ROM 20, and the result is stored in the RAM 19.

22 is a clock generator, and the clock generated here is divided into 1/n by a frequency divider 23 and supplied to the CPU 21 and the analog/digital converter 17 as a system clock _Sh .

The CPU 21 outputs the timing for determining the waveform of the excitation current I _f to the timing signal output port (TO) 24 via the bus 18 in accordance with the arithmetic program stored in the ROM 20 . The timing signal output port 24 outputs timing signals S ₂ , S ₃ , S ₄ , and S ₅ for switching the excitation current according to this timing.

In addition, the timing signal output port 24 is
Timing signal according to the timing specified by 21
S _l is output to an analog/digital converter 16 and the output of the preamplifier 14 is sampled.

On the other hand, using the data stored in RAM 19 by the calculation program stored in ROM 20,
A predetermined calculation is executed by the CPU 21, and the result of the calculation is stored in the RAM 19 and the bus 1
8, the digital/analog converter 25, and the output end 26 as a flow rate output.

Further, the saturation detector 27 receives a signal from the preamplifier 14, and detects whether or not the preamplifier 14 is saturated due to, for example, flow noise. The signal detected here is output to a data input port (DI) 28 and stored as a digital signal in a predetermined area of the RAM 19 under the control of the CPU 21 via the bus 18.

Next, the basic operation of the embodiment shown in FIG. 1 will be explained based on the flowchart shown in FIG. 2 with reference to other drawings.

In step 1 shown in FIG. 2, the power is first turned on. The CPU 21 detects this state in step 2.

Based on this result, the CPU 21 enters initialization processing (step 3). This initialization process is performed by, for example, the analog/digital converter 16,
Hardware reset such as 17 or RAM19
Make necessary preparations for subsequent signal processing, such as securing a calculation area and a flag area.

The system clock S _h obtained from the output of the frequency divider 23 shown in FIG. 1 has the waveform shown in FIG. 3 a, and is supplied to the CPU 21. In synchronization with the interrupt timing of clock S _h (Fig. 3g)
A timing signal indicating switching timing of the excitation waveform is outputted to the timing signal output port 24 via the bus 18 according to a predetermined calculation program stored in the ROM 20 .

In step 4, the timing signal output port 24 receives this switching timing and outputs timing signals S ₅ (FIG. 3b), S ₄ (FIG. 3c), S ₃ (FIG. 3d), and S ₂ (FIG. 3d). Figure e) is output to the switches SW ₅ , SW ₄ , SW ₃ , and SW ₂ of the excitation circuit 13, respectively. Alternatively, output the timing signal S ₄ to the switches SW ₃ and SW ₄ at the same time, and output the timing signal S ₂ to the switch SW 3 and SW 4 simultaneously.
Output to SW ₂ and SW ₅ simultaneously. The excitation circuit 13 receives these timing signals and outputs an excitation current I _f having a waveform shown in FIG. 3f to the excitation coil 12. This excitation waveform is a waveform in which the timing number i is 0 to 15, forming one cycle and repeating this, as shown in Fig. 3 h and i, and Fig. 3 mainly shows the n cycle part. . This excitation waveform has a multiplicative waveform obtained by multiplying a low frequency waveform and a high frequency waveform.

Next, proceed to step 5. In step 5, the saturation detector 27 receives the signal voltage from the preamplifier 14 and outputs it to the data input port 28 as an alarm signal ALM. CPU21 is the third
Data is taken in from the data input port 28 and stored in the alarm area of the RAM 19 at the interrupt timing shown in FIG.

In step 6, the CPU 21 compares the alarm signal ALM stored in step 5 with the set value stored in the ROM 20 to determine whether there is any abnormality. If not normal, proceed to step 7.

In step 7, a predetermined output stored in the ROM 20 as an abnormal output is set, for example, 0% output or 100% output.
The output and the like are outputted to an output terminal 26 via a bus 18 and a digital/analog converter 25.

In step 8, the alarm signal is output in the same manner as in step 5 at the next interrupt timing (Fig. 3g).
Enter ALM. For this result, step 9
Then, the CPU 21 determines whether or not the preamplifier 14 is saturated in the same manner as in step 6. If it is not normal, the process returns to step 7 and continues to output the abnormality output. If it is normal, the process moves to step 10 in the same way as when it is determined to be normal in step 6.

In step 10, analog/digital converter 1
Read data from 6 and 17. This reading procedure will be explained in detail using the flowchart shown in FIG.

In step 10A, the interrupt timing (third
Analog/digital converter 17 in synchronization with Figure g)
As shown in FIG. 3j, the data input from
is stored in a predetermined data area H _i of .

Next, the process moves to step 10B, and it is determined whether or not the read timing number i is 0. If it is not 0, the process moves to step 10C, and if it is 0, the process moves to step
Move to D.

In step 10C, it is determined whether the read timing number i is 8 or not. If it is not 8, the data reading is finished, and if it is 8, the process moves to step 10E.

In step 10D, the data _input from the analog/digital converter 16 is transferred to the bus 18 as shown in FIG. via CPU2
Based on the control of 1, a predetermined data area of RAM 19...
..., L ₀ (n-1), L ₀ (n), L ₀ (n+1), . . . and end the data reading.

At step 10E, the data _input from the analog/digital converter 16 is transferred to the bus 18 as shown in FIG. via CPU2
Based on the control of 1, a predetermined data area of RAM 19...
..., L ₁ (n-1), L ₁ (n), L ₁ (n+1), ..., and the reading of the data is completed.

With the above procedure, the data reading shown in step 10 is completed.

Next, the process moves to step 11. Step 11
Then, it is determined whether or not data reading in step 10 has been executed a predetermined number of times. If the predetermined number of readings have not been completed, proceed to step 10.
When the predetermined number of times has been reached, the process moves to the next step 12. These read data are stored in a predetermined area of the RAM 19. This step is necessary because the high-frequency demodulated signal is
This is because it is necessary to calculate e _Hi (Fig. 3 m).

In step 12, the calculation time constant T for flow rate calculation is
The CPU 21 reads the initial value from the ROM 20 in preparation for calculation. This calculation time constant T is set to the minimum value.

In step 13, the initial values necessary for flow rate calculation are
Read from ROM20.

In step 13, the initial value of the flow rate signal is calculated. The details of this flow rate calculation will be described later, but
Basically, the flow rate calculation is performed using the high-frequency demodulated signal e _Hi obtained by demodulating the signal voltage at high frequency, and the high-pass filtered signal F _Hi obtained by high-pass filtering calculation, and the low-frequency demodulated signal obtained by demodulating the signal voltage at low frequency. It is obtained by adding the low-pass filtered signal F _Li obtained by low-pass filtering using e _Li .

This high-pass filtered signal F _Hi is given by the following equation, assuming that ΔT _H is the operation period shown in FIG. 3f.

F _Hi = (F _Hi-2 +e _Hi −e _Hi-2 )×T/(T+ _ΔTH )…(1
) However, e _Hi-2 and F _Hi-2 are the high-frequency demodulated signal and high-pass filtered signal read last time. Further, the high frequency demodulation signal e _Hi is a value obtained by the calculation formula shown in the column of high frequency demodulation calculation in FIG.

In this case, the initial value is F _Hi-2 = 0,
Set e _Hi-2 = e _Hi . This is F _Hi as the initial value
= 0.

On the other hand, the low-pass filtered signal F _Li is given by the following equation.

F _Li =F _Li-8 + (e _Li −F _Li-8 )×T/(T+ΔT _H )…(2
) Here, F _Li-8 is the value of the previous low-pass filtered signal F _Li . And, as the initial value in this case, F _Li-8 =
Set up _eLi . This means F _Li =e _Li , and the signal voltage input this time will be output as a low-pass filtered signal. Note that ΔT _H =8ΔT _L.

Therefore, the sum of the low-pass filtered signal and the high-pass filtered signal becomes the high-frequency demodulated signal obtained this time, and this is sent to the output end 2 as the initial flow rate output via the CPU 21 and the digital/analog converter 25 in step 15.
Output to 6. Initial settings are completed with steps 10 to 15 above.

Next, the process moves to step 16. Step 16
But as in step 5, data input port 2
An alarm signal is input from step 8, and in the same way as step 6, it is determined whether the signal voltage is normal or not at step 17. If it is normal, return to step 7 and process the abnormality, and if normal, proceed to step 18.
to move to.

In step 18, data is sequentially transferred to the RAM 1 in the same manner as in step 10 according to the procedure shown in FIG.
Load into 9.

Further, in step 19, the calculation time constant T set in step 12 is reset to a larger value than that in step 12 according to the procedure stored in the ROM 20, and the process proceeds to step 20.

At step 20, the flow rate is calculated using the reset calculation time constant (Tc). This flow rate calculation will be explained in detail using FIG. 5.

At step 20A in FIG. 5, it is determined whether the timing number i is an odd number or not. If it is an odd number, the process moves to step 20B, and if it is not an odd number, it is judged that the process moves to step 20D.

Step 20B performs high frequency demodulation calculations. In the demodulation calculation, data H _i stored in the RAM 19 is used, and the CPU is activated at the timing shown in Figure 3 m.
Under the control of 21, the high frequency demodulation calculation shown in _FIG . Through this demodulation calculation, the electrochemical DC voltage generated across the electrodes 11a and 11b is removed, and the differential noise is kept at a constant value and does not become an error factor.

Next, the process moves to step 20C. Here, a high-pass filtering operation F _Hi on the high frequency side is executed.

When performing filtering calculations, the CPU uses data e _Hi stored in the RAM 19 and the previous filtering calculation results.
Under the control of 21, the high-pass filter calculation F _Hi shown in FIG. In addition, the constant A in Fig. 6 is A = Tc / (Tc +
ΔT _H ).

Next, the process moves to step 20D. In step 20D, it is determined whether the timing number i is 0 or 8, and if it is 0 or 8, the process moves to step 20E.
If it is not 0 or 8, it is determined to proceed to step 20G.

In step 20E, low frequency demodulation calculations are performed. During the demodulation calculation, the data stored in the RAM 19..., L ₀ (n-1), L ₀ (n), L ₀ (n+
1),...L ₁ (n-1), L ₁ (n), L ₁ (n+1),...
..., the CPU 2 at the timing shown in Figure 3n.
Under the control of 1, the low frequency demodulation calculation shown in _FIG .

In step 20F, low-pass filter calculation on the low frequency side is performed.
Run F _Li .

When performing the filtering calculation, the data e _L0 and e _L8 stored in the RAM 19 and the previous filtering calculation result are used.
Under the control of the CPU 21, calculations are performed using the calculation formula shown in the column of low-pass filter calculation F _Li shown in FIG. 6, which is stored in the ROM 20, and the results are stored in the RAM 19. In addition, in FIG. 6, the constant B is B=ΔT _L /
It is expressed as (ΔT _L +Tc).

In step 20G, it is determined whether or not the timing number i is an odd number. If it is an odd number, the process moves to step 20H, and if it is not an odd number, the flow rate calculation is ended.

Step 20H performs an addition operation. RAM
Using the result F _Hi of the high-pass filter calculation stored in 19 and the result F _Li of the low-pass filter calculation stored in the ROM 20 under the control of the CPU 21, the addition calculation shown in the column _eA shown in FIG. 6 is performed. Perform calculations using arithmetic expressions and obtain the results.
It is stored in the RAM 19 and the flow rate calculation is completed.

As described above, the signal voltage containing two frequencies, a low frequency and a high frequency, detected by the electrodes 11a and 11b is
The low frequency side and the high frequency side are read separately using a microcomputer, and the low frequency side is demodulated at low frequency and its output is passed through a low-pass filter, and the high frequency side is demodulated at high frequency and output. are output through a high-pass filter, and these are added to form a flow rate signal, and the process moves to step 21.

In step 21, the calculated result of the flow rate is outputted via the bus 18 and the digital/analog converter 25. After outputting the above flow rate output, the process moves to step 22.

In step 22, it is determined by a predetermined program stored in the ROM 20 whether or not a predetermined calculation time constant value has been reached. If the predetermined value has not been reached, the process returns to step 16 and the calculations up to step 22 are repeated again. When the predetermined value is reached, the process moves to step 23.

The calculations in steps 16 to 22 above show a time constant changing procedure in which the calculation time constant is set small at first and then gradually increased so that a steady flow rate output can be produced quickly.

From step 23 to step 27, the calculation time constant set in the time constant changing procedure is fixed, and a steady flow rate calculation is executed. This calculation is the same as the flow rate calculation in which the time constant is kept constant, except for steps 19 and 22 among the steps 16 to 22.

Note that FIG. 7 shows a modified embodiment of the time constant changing means.

In this embodiment, instead of resetting the calculation time constant many times and outputting the flow rate each time, the calculation time constant is set to the maximum value after a predetermined period of time has elapsed.

Therefore, in FIG. 7, step 19 is omitted, and instead, a coefficient procedure for counting time is provided after step 21 (step 28), and further step 29 is provided for determining whether a predetermined time has elapsed. . If the predetermined time has not elapsed in step 29, the process returns to step 16, and if it has elapsed, the calculation time constant is set to the maximum value in step 30, and the process proceeds to step 23 to execute normal flow rate calculation.

Further, in FIG. 2, steps 20 and 21
A procedure is established to calculate the moving average of the flow rate between the
It is also possible to smooth the flow rate output value.

As described above in detail along with the embodiments, according to the present invention, the time constant can be varied in an electromagnetic flowmeter with a dual excitation method of low frequency and high frequency. It is possible to significantly shorten the time it takes to transition to a steady state when this happens or when a normal state returns from an abnormal state.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a flowchart showing the operation procedure of the embodiment shown in FIG. 1, FIG. 3 is a timing diagram explaining the timing of the operation of the embodiment shown in FIG. 1, and FIG. Flowchart diagram illustrating the procedure for reading data in the flowchart shown in FIG.
The figure is a flowchart diagram showing the procedure for calculating the flow rate in the flowchart shown in Figure 2, Figure 6 is a calculation diagram showing the calculation procedure for calculating the flow rate in the flowchart shown in Figure 5, and Figure 7 is a calculation diagram showing the procedure for calculating the flow rate in the flowchart shown in Figure 5. FIG. 7 is a flowchart showing a modified example of the time constant changing procedure shown in the figure. 10... Conduit, 12... Excitation coil, 13...
Excitation circuit, 14... Preamplifier, 16, 17...
Analog/digital converter, 18...Bus, 19
... Random access memory, 20 ... Read only memory, 21 ... Processor, 22 ... Clock generator, 24 ... Timing signal output port, 27 ... Saturation detector, 28 ... Data input port.

Claims (1)

[Claims] 1 Excitation means for supplying magnetic fields having two different frequencies, a first frequency and a second frequency lower than the first frequency, and a signal voltage excited by the excitation means and generated corresponding to the flow rate based on the first frequency. a first demodulation calculation means for discriminating and outputting;
a high-pass filter calculation means for high-pass filtering the output of the demodulation calculation means with a large high-frequency time constant; a second demodulation calculation means for discriminating and demodulating the signal voltage based on the second frequency; and the second demodulation calculation means. a low-pass filter calculation means for low-pass filtering the output of the means with a large low-pass time constant, and algebraic synthesis using each output of the high-pass filter calculation means and the low-pass filter calculation means to calculate the flow rate output. a determining means for determining whether or not the calculation state is suitable for calculating the normal flow rate output corresponding to the signal voltage; An electromagnetic flowmeter comprising time constant changing means for initially setting the high-frequency time constant and the low-frequency time constant to a small value and then increasing the value.