JPH0376405B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention eliminates the effects of sudden changes in the DC potential between electrodes, such as DC noise voltage based on electrochemical factors contained in the received signal from an electromagnetic flowmeter transmitter. This invention relates to an electromagnetic flowmeter converter with an improved signal processing method.

<Prior art> The received signal from the electromagnetic flowmeter transmitter includes electromagnetic induction noise voltage caused by temporal changes in excitation magnetic flux density, DC noise voltage generated due to electrochemical factors between the electrode and the fluid, and commercial Since various kinds of noise are included in the commercial frequency noise voltage caused by the power supply, various signal processing methods have been proposed to remove the noise.

Regarding the removal of electrochemical DC noise, please refer to Japanese Patent Application Laid-open No. 128551/1986 (Title of invention: ``Electrochemical interference DC voltage compensation method for electromagnetic flowmeter using DC magnetic field switched between two degrees of magnetic induction'') ) and Tokukai Sho
Techniques such as No. 54-896568 (title of invention: "Inductive flow rate measuring method and device") are known. These techniques are based on the assumption that electrochemical DC noise changes sufficiently slowly compared to the excitation period, and therefore are not necessarily effective when the inter-electrode DC potential suddenly changes. That is, it has been found that, in reality, electrochemical DC noise suddenly changes over a period of about 10 msec to 1 sec, and the amplitude of the sudden change is extremely large compared to the flow rate signal.

Therefore, the patent application No. 57-4911 focused on the fact that the rate of change in the received signal due to sudden changes in the DC potential between the electrodes is much larger than the rate of change due to flow velocity, and proposed a signal processing method that eliminates the effects of sudden changes. (Name of invention: "Magnetic flowmeter converter"). That is, the time-series average value of the received signal values from the electromagnetic flowmeter transmitter is calculated and output, and the range of a fixed width above and below the average value is set as a normal signal area, that is, a window, following this average value. It is determined whether the new received signal value is within this window, and if it is inside the window, the new received signal value is used to calculate the average value, but if it is outside the window, the new received signal value is used. Instead, the window boundary value or the calculated average value is used to calculate the average value.

FIG. 1 shows an embodiment of this conventional system. In the figure, 1 is an electromagnetic flowmeter transmitter, measurement pipe 2,
The transmitter 1 is composed of electrodes 3 _a and 3 _b and an exciting coil 4, and is excited by controlling the changeover switches SW _1-1 to SW _1-4 using a signal i from a timing circuit 5. The output of the oscillator 1 passes through a high input impedance amplifier 6 and then receives the signal j from the timing circuit 5.
Synchronous rectification is carried out by a synchronous rectification circuit comprising changeover switches SW _2-1 and SW _2-2 and an amplifier 7, which are controlled according to the excitation polarity. The output a of this synchronous rectifier circuit is normally input to the averaging circuit 8 via the switch SW _3-2 , where it is averaged in time series and output as an output signal d proportional to the flow velocity.

9 _a and 9 _b are comparators; one comparator 9 _a
is the lower limit value g=d−f obtained by subtracting a certain constant value f given by the DC power supply from the averaged output signal d.
and the synchronous rectification output a, and when a<g, the switch SW _3-1 is connected to the averaging circuit g based on the comparison output b, and the value of g=d−f is given. The other comparator 9 _b has an upper limit boundary value h= which is obtained by adding a certain constant value e given by the DC power supply to the averaged output signal d.
d+e and synchronous rectification output a are compared, and when a>h, the switch SW _3-3 is connected to the averaging circuit 8 based on the comparison output c, and the value h=d+e is given. Note that 10 is an addition circuit, and 11 is a subtraction circuit.

As described above, the input signal to the averaging circuit 8 is subjected to window processing using the upper and lower boundary values d+e and d−f defined by the averaged output signal d and constant values e and f.

Therefore, if the received signal from the transmitter 1 suddenly changes, the synchronous rectifier output a will naturally change suddenly, and the averaging circuit 8
Since d−f or d+e is input instead of the sudden change signal, fluctuations in the averaged output signal d can be suppressed. If the constant values e and f are set to small values, the response characteristics of the averaged output signal d will worsen, but in general, a sudden change in the inter-electrode DC potential shows a much larger rate of change than a flow velocity fluctuation, so e and f Even if the output voltage is set to a certain degree, such as about 50% of the output span, it is possible to suppress the influence of sudden changes on the output while ensuring a sufficiently fast response characteristic against sudden changes.

However, the above conventional technology is effective when the frequency of sudden changes in electrochemical DC noise is low, but when the frequency of occurrence increases, the received signal due to changes in flow rate and sudden changes in electrochemical DC noise are This has the disadvantage that it becomes difficult to distinguish it from the received signal, resulting in a slow output response speed of the electromagnetic flow meter converter to changes in flow rate. For example, the frequency of occurrence of electrochemical DC noise increases, and the upper and lower boundary values d-
If the condition exceeding f and d+e continues, the output of the averaging circuit will be clamped to the average value of d-f and f+e, and a state will occur where it will not follow the actual flow rate change, resulting in a decrease in the response speed of the output of the electromagnetic flow meter converter. The disadvantage is that it is slow.

<Object of the Invention> In view of the above-mentioned prior art, an object of the present invention is to provide an electromagnetic flowmeter that eliminates the influence of sudden changes in the inter-electrode direct current potential even when they occur continuously.

<Configuration of the Invention> FIG. 2 is an overall configuration diagram for clearly showing the configuration of the present invention. The received signal from the transmitter is passed through an amplifier that can change the amplification level and compared to see if the received signal is within a predetermined boundary value. If it is within the boundary value, the new received signal is output as is as a flow rate output. do. This boundary value follows the received signal after passing through the amplifier, and is set at a constant ratio to the received signal within a constant width range above and below the received signal. When the received signal falls outside the above boundary value range, the degree of fluctuation caused by the sudden change in DC potential is detected, and when the degree of fluctuation is small, the previously received received signal is output as the flow rate output. On the other hand, it is further determined whether the frequency of the fluctuation is within an allowable range, and if it is outside the allowable range, the excitation current of the oscillator is increased, and at the same time, the amplification degree of the amplifier is adjusted according to the degree of increase in the excitation current. Make small changes. With this configuration, it is possible to improve the signal-to-noise ratio (S/N ratio) of the received signal to the converter, reduce the number of fluctuations in the boundary value, and improve responsiveness.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows the overall arrangement of the components of this embodiment. Parts having the same functions as those in FIG. 1 are designated by the corresponding reference numerals, and their explanations are omitted. Excitation coil 4
are arranged so as to generate a magnetic field perpendicular to both the flow direction of the fluid in the measurement pipe 2 and the mounting direction of the electrodes 3 _a and 3 _b in the measurement pipe 2 . Excitation coil 4 is switched from DC current source I.
The configuration is such that the excitation current If is supplied via SW _1-1 to SW _1-4 and further through the detection resistor 12 that detects the excitation _current . The constant multiplier amplifier 6 is an amplifier that amplifies the signal voltage generated between the electrodes 3 _a and 3 _b with a high input impedance. Output of amplifier 6 and detection resistor 12
The comparison voltage V _r obtained is switched by a changeover switch 13 and amplified by a variable gain amplifier 14 . The output signal of the variable gain amplifier 14 is input to an analog-to-digital converter (hereinafter abbreviated as an A/D converter) 15 which also serves as a signal sampler. 16 is a microprocessor (hereinafter referred to as CPU)
), 17 is memory (ROM/RAM),
18 is an input/output port (I/O), 19 is a digital/analog converter (hereinafter referred to as a D/A converter), 20 is an address bus, 21 is a data bus,
22 is a flow rate output. A program for controlling the CPU 16 is written in the ROM of the memory 17, and the CPU 16 performs I/O according to this program.
Arithmetic processing is performed while importing the required signal data from the O port 18, controlling the excitation current I _f and the variable gain amplifier 14, or exchanging data with the RAM of the memory 17. Then, the processed data is output to the I/O port 19 as necessary. The D/A converter 19 converts the data provided from the I/O port 18 into an analog signal and outputs it. Reference numeral 23 denotes a switching control circuit for switching the changeover switches SW _1-1 to SW _1-4 at timings specified by the CPU 16 to obtain the excitation current _If in three states. 24 is a current control circuit for changing the magnitude of the current of the DC current source I in accordance with a control signal from the CPU 16. The changeover switch 13 and the variable gain amplifier 14 are each controlled by a control signal from the CPU 16.

The operation of the electromagnetic flowmeter converter of this embodiment configured as described above will be explained using the waveform diagram of FIG. 4 and the flowchart of FIG. 5.

First, the signal processing program will be explained (steps from FIG. 5). The switching control circuit 23 is controlled at the timing specified by the excitation current control program written in the ROM of the memory 17 to switch the changeover switches SW _1-1 to SW _1-4 to set the excitation current as shown in FIG. 4a. Create I _f and excite oscillator 1 in three states. Accordingly, a comparison voltage V _r having a waveform shown in FIG. 4b is generated in the detection resistor 12.
When the fluid flows through the measuring pipe 2, a flow rate signal shown in FIG. 4c is obtained which has a waveform substantially the same as that of the excitation current. Four sample values S ₁ to _{S 4} of this flow rate signal are read as one cycle from the A/D converter and stored in the RAM at the timing shown in FIG. 4b. The sample data stored in this manner is subjected to the calculation shown in the following equation, for example, by the CPU 16, and slow DC noise is removed, resulting in a flow rate signal _E1 .

E ₁ =S ₁ +S ₂ -S ₃ -S _4Such calculations are repeatedly executed, and a flow rate signal _Eo for each cycle is obtained one after another. On the other hand, the comparison voltage V _r is 10% with respect to the sample period of the flow rate signal E _o
The changeover switch 13 is switched to the comparison voltage side by a control signal from the CPU 16 with a cycle of 20 times to 20 times, and the comparison voltage V _r is taken into the A/D converter 15 by an interrupt, digitally converted, and stored in the memory 1.
7 RAM.

The flow rate signal E _o obtained in this way and the comparison voltage
V _r is divided by E _o /E _r by the CPU 16 to obtain a received signal E _s . This is to eliminate output errors due to fluctuations in the excitation current _If .

Next, window processing will be explained (steps ~ in Fig. 5). The received signal E _s processed as above
The CPU 16 calculates the upper and lower boundary values within a fixed width range of the received signal using the ratio stored in advance in the ROM of the memory 17, and calculates the newly received reception value for the calculated upper and lower boundary values C. signal
A comparison is made between E _s and the previously received received signal E _s-1 . That is, it is the absolute value of the difference between the newly received received signal E _s and the previously received received signal E _s-1 |E _s −
If E _s-1 | is smaller than the above-mentioned boundary value C, it is determined that there is no sudden change in the DC potential between the electrodes in the newly received received signal E _s , and the new received signal E _s is Output as output. If the absolute value of the difference between the new received signal E _s and the previous received signal E _s-1 |E _s −E _s-1 | is larger than the boundary value C, it is determined that there has been a sudden change in the DC potential, and the next Shift to the vibration detection program.

Oscillation detection (steps ~ in FIG. 5) is performed as follows. As a result of the window processing, if it is determined that there has been a sudden change in the DC potential, an area for the counter M is provided in the RAM of the memory 17, so the count content in this area is set to +1. Corresponding to the count contents of this part, a counter L different from counter M is created in RAM in the same way.
Since this area is provided, the count content of this part is set to +1. Next, the direction of change of the new received signal _Es is compared with the direction of change of the previously received received signal, and if they are not in the same direction, it is determined that the change is due to a sudden change in the DC potential, and the contents of the counter L are reset. That is, the contents of the counter M are counted and updated both when the flow rate exceeds the boundary value C due to a rapid change and when the boundary value C is exceeded due to a sudden change in the DC potential. counter L
Of the contents exceeding the boundary value C, those due to sudden changes in DC potential are reset, and only cases based on changes in flow rate are counted. This is because the change in potential due to a sudden change in DC potential is shorter than the change in flow rate and changes in a pulse-like manner, so a change in the received signal in the same direction is judged as a change in flow rate, whereas a sudden change in DC potential This is to make a judgment based on the fact that the direction of change is opposite. Therefore,
When the received signals change in the same direction, that is, the number determined to be a flow rate change is stored in a counter L. For counter L, there is a program in ROM that determines whether the count value has reached the set value _N1 .
If the set value _N1 has not been reached by executing this judgment program, the process returns to step (FIG. 5) and the processes up to now are repeated. When returning to the step, the previously received reception signal is output as the flow rate output. This is because the received signal exceeds the boundary value, so it is determined that it is more appropriate to output the previous received signal. There is a counter P in the RAM of memory 17.
When the count value of the counter L reaches the set value _N1 set in the ROM, the contents of the counter P are updated to +1. At the same time, the contents of the counter L are reset to return to the initial state. Therefore, the counter P stores the number of changes in the received signal in the same direction, that is, the number of times the flow rate fluctuates. In the above manner, the counter M
Since the number of changes in the received signal is stored in the counter P, and the number of flow rate fluctuations is stored in the counter P, when the CPU 16 calculates M/P using these values, the result Q is the received signal with respect to the flow rate fluctuation. It refers to the ratio of the number of changes in . When Q is small, it is determined that the value of P has increased because there is a lot of flow rate fluctuation, and when the value of Q is large, it is determined that M has become large even though there is no flow rate fluctuation, that is, the number of sudden changes in the DC potential has increased. I can judge. Therefore, the degree of sudden change in DC potential can be determined based on the value of Q.

It is the fluctuation determination shown in steps ~ in the flowchart of FIG. 5 that determines whether the degree of sudden change in the DC potential is within an allowable range. The above tolerances
_N2 and this judgment program are stored in ROM. When the value of Q is equal to or smaller than the allowable value _N2 , the process returns to the steps of the flowchart described above and the processing up to now is repeated. However, when the value of Q exceeds _N2 , the degree of sudden change in DC potential is unacceptable, and a program is entered to change the excitation current.

The procedure for changing the excitation current is shown in steps ~ in the flowchart of FIG. When the value of Q exceeds N ₂ , the excitation _current If is increased stepwise. In this case, the CPU 16 determines whether the increased value of the excitation current is within the allowable range of the transmitter 1, and if it is outside the allowable range, an alarm is issued and, for example, the operation is stopped. If it is within the allowable range, the comparison voltage V _r is newly written to the RAM of the memory 17 by interrupt processing.

At the same time as changing the excitation current, the amplification degree of the variable gain amplifier 14 is decreased in accordance with the increased value of the excitation current, as shown in steps ~ in the flowchart of Fig. 5, so that the flow rate signal remains the same as before the excitation current was increased. value. This is to ensure that the A/D converter 15 falls within a proper operating range. After this process, return to step.

Through the processing in steps 1 to 3 above, the ratio of the sudden change value of the DC potential to the flow rate signal, that is, the S/N ratio is improved. That is, the sudden change in the DC potential depends on the type of electrode material, the flow rate, the type of fluid, etc. and is unrelated to the excitation current, but the flow rate signal increases by the same amount as the excitation current increases. After increasing the excitation current, repeat the process in step ~ above, and if it is determined that the received signal is within the boundary value by the window processing shown in step ~, the increase in the excitation current is stopped at that stage and the received signal is is output as a flow rate output. The excitation current is step~
If, for example, there is no case where the value outside the boundary value exceeds the boundary value for a long period of time, the excitation current is gradually reduced to return to the initial state, thereby reducing power consumption. In this example, we have explained the case where the excitation current is changed in stages, but it may be changed continuously as necessary, or the excitation current may be changed in only one stage. good.

<Effects of the Invention> According to the configuration in which the content of the present invention has been specifically explained through the embodiments as described above, the following effects are produced.

(b) When the number of sudden changes in the DC potential increases and the excitation electromagnetic force is increased, the ratio of the sudden change value of the DC potential to the received signal becomes smaller, and the boundary value width C is set in relation to the value of the received signal. The number of times the boundary value width C is applied is reduced, and the responsiveness, which is a drawback of the prior art, is significantly improved.

(b) Even when there are many sudden changes in the DC potential, the excitation current is increased to improve the S/N ratio of the received signal, making it possible to measure the flow rate without being affected by sudden changes in the DC potential.

(c) When there are few sudden changes in the DC potential, efficient flow measurement can be performed with a small excitation current, and low power consumption can be achieved.

(iv) According to the present invention, fluids that are prone to sudden changes in direct current potential or fluids that are difficult to cause can be used without any particular consideration, thereby expanding the field of application of flow rate measurement.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional example, Fig. 2 is a block diagram showing the overall configuration of the present invention, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 shows a flow rate signal in the present invention. FIG. 5 is a timing diagram showing the sampling timing, and is a flowchart of the signal processing in FIG. 3. In the drawing, 1 is a transmitter, 13 is a changeover switch, 1
4 is a variable gain amplifier, 15 is an A/D converter, 1
6 is CPU, 17 is memory, 18 is I/O port,
19 is a D/A converter, 22 is a flow rate output, 23 is a switching control circuit, 24 is a current control circuit, I is a constant current source, and SW _1-1 to _{SW 1-4} are changeover switches.

Claims (1)

[Claims] 1 Boundary value setting means for following a received signal from an electromagnetic flowmeter transmitter and setting upper and lower boundary values within a fixed width range above and below the received signal at a constant ratio to the received signal, and a new received signal. a comparison means for comparing a value with upper and lower boundary values; a fluctuation detection means for detecting a fluctuation in the received signal when the received signal value exceeds the boundary value; oscillation determination means for determining whether the value exceeds the value of
excitation current changing means for changing the excitation current of the transmitter based on the determination result of the fluctuation determining means; and amplification degree changing means for changing the amplification degree of an amplifier for amplifying the received signal in accordance with the excitation current. The electromagnetic device is characterized in that when the received signal value is within the boundary value, the new received signal is output, and when the received signal value is outside the boundary value, the previously received received signal is outputted. Flow meter converter.