JPH0318133B2

JPH0318133B2 -

Info

Publication number: JPH0318133B2
Application number: JP7918382A
Authority: JP
Inventors: Hitoshi Akyama
Original assignee: Yokogawa Electric Corp
Current assignee: Yokogawa Electric Corp
Priority date: 1982-05-13
Filing date: 1982-05-13
Publication date: 1991-03-11
Also published as: JPS58196420A

Description

[Brief explanation of the drawing]

第１図は本発明の実施例を示すブロツク線図、
第２図ａ〜ｆはその各部の波形を示す波形図、第
３図ａ，ｂは電源周波数の変動に伴なうスパン変
動を説明するための波形図で、第３図ａが50Hzの
場合、第３図ｂが60Hzの場合である。第４図は前
記実施例におけるマイクロコンピユータのフロー
チヤート、第５図は本発明の他の実施例を示す回
路図である。図面中、８は商用電源、９はプリアンプ、１１
はCPU、１２はROM、１４はコンデンサ、１５
はカウンタ、V₀は実測流量値、Vsは出力である。 FIG. 1 is a block diagram showing an embodiment of the present invention;
Figures 2 a to f are waveform diagrams showing the waveforms of each part, Figures 3 a and b are waveform diagrams to explain span fluctuations due to fluctuations in power supply frequency, and Figure 3 a is for 50Hz. , Fig. 3b is for the case of 60Hz. FIG. 4 is a flow chart of the microcomputer in the embodiment, and FIG. 5 is a circuit diagram showing another embodiment of the present invention. In the drawing, 8 is a commercial power supply, 9 is a preamplifier, and 11 is
is CPU, 12 is ROM, 14 is capacitor, 15
is a counter, V ₀ is the measured flow rate value, and Vs is the output.

Claims

[Claims] 1. An electromagnetic flowmeter has a counter that detects the frequency of the commercial power source, and the measured flow rate value is multiplied by a predetermined correction coefficient corresponding to the frequency detected by the counter. An electromagnetic flowmeter characterized by output. [Scope of Claims] The present invention relates to an electromagnetic flowmeter that has been improved so that the influence of fluctuations in power frequency can be automatically corrected. In conventional electromagnetic flowmeters, the power frequency is 50Hz.
When the frequency changes from
The span is adjusted to 55Hz to reduce the influence of span fluctuations. However, among these conventional techniques, the former has the problem that the number of models has increased, which hinders standardization, and the latter cannot sufficiently eliminate the effects of span fluctuations. SUMMARY OF THE INVENTION In view of the above prior art, an object of the present invention is to provide an electromagnetic flowmeter that can automatically correct span fluctuations due to fluctuations in power frequency. The present invention, which achieves this object, is based on the technical concept of measuring the power supply frequency and multiplying the output by a predetermined coefficient according to the value of the frequency. Embodiments of the present invention will be described in detail below based on the drawings. The electromagnetic flowmeter shown in FIG. 1 is a constant current driven, low frequency excitation type electromagnetic flowmeter that uses a microcomputer for signal processing. To briefly explain the basic configuration and operation of an electromagnetic flowmeter, the excitation circuit 5 synchronizes with the commercial power supply 8 to remove inductive noise at the commercial frequency.
An excitation current having a frequency such as 8 is generated and supplied to the excitation coil 1. Excitation current waveforms are positive/negative, positive/zero, negative/
Any polarity such as zero, positive/zero/negative/zero, or sine wave, triangular wave, or trapezoidal wave may be used, but here we use a rectangular wave excitation with repeating positive/zero/negative/zero as shown in Figure 2 a. This will be explained using current as an example.
In response to this excitation current, a flow rate proportional signal shown in Fig. 2b is generated between the electrodes 3a and 3b fixed to the measuring pipe 2, but this is accompanied by electromagnetic induction noise shown in Fig. 2c, and d in the same figure. The commercial frequency noise shown in Fig. 2 and the electrochemical DC noise shown in Fig. So preamp 9
The amplified output of is converted into a digital signal by an A/D converter (analog-to-digital converter) 10, and
At timings a, b, c, d, . . . , the sample values Va, Vb, Vc, Vd are taken into the CPU (microcomputer) 11. The CPU 11 operates according to a program stored in the ROM (read-on memory) 12, and in this example calculates the flow rate value Vs by calculating the following equation (1) using sample values.
I am getting . However, K is a proportionality constant. vs=K(-Va+3Vb-3Vc+Vd)...Equation (1) In other words, the sample value at each timing has a second
The shaded parts in the waveforms in Figures a to e are included as components, but for electromagnetic induction noise, each sample timing is the same time t from the point of change of the excitation current, so for commercial frequency noise, the sample timing is commercial By being synchronized with the frequency, the electrochemical noise can be considered to change by a constant variable ΔE for each sampling because the sample timing is at equal intervals and in a short period of time like the excitation period, so that the equation (1) Each noise component is canceled out and removed by the calculation. The flow rate value Vs thus obtained is output as a signal in a predetermined output format by a D/A converter (digital/analog converter) 13 or the like. At this time, preamplifier 9 and A/D
A capacitor 14 is interposed between the converter 10 and the converter 10. This is to remove the DC potential generated from the electrodes 3a and 3b, and the capacitor 14
The preamplifier 9 and A/D converter 10 are connected to AC
are combined. Therefore, the flow rate proportional signal shown in FIG.
When changing to Hz, not only the period but also the waveform (corresponding to the shape of the attenuation curve) changes, as shown in FIGS. 3a and 3b. Incidentally, if Fig. 3 a is 50Hz,
Figure 3b shows the case of 60Hz. Therefore, the third
As is clear from FIGS. a and b, the signal amount at the time of sampling (indicated by diagonal lines in both figures) changes, causing span fluctuations. Therefore, in this example,
Focusing on the fact that the span variation depends on the capacitance of the capacitor 14, the span variation is determined in advance, and a frequency correction table based on this is created in the ROM 12. That is, a table in which correction coefficients corresponding to power supply frequencies are determined as shown below is formed in the ROM 12. [Table] [Table] On the other hand, the power frequency of commercial power supply 8 is calculated by counter 15.
It has finally been detected by Therefore, CPU1
1 is based on the flowchart shown in FIG.
After reading the current power supply frequency, which is information from the counter 15, and subsequently reading the correction coefficient Kn corresponding to that frequency from the ROM 12, the correction coefficient Kn is applied to the measured flow rate value Vs, which is the output of the A/D converter 10. Multiply to calculate V ₀ =Vs·Kn and output it. Therefore, the output V ₀ is not affected by span fluctuations due to frequency fluctuations of the commercial power supply 8. At this time, the gain adjustment of the converter was performed at 50Hz. Note that 16 in FIG. 1 is a RAM (random access memory) used for storing sample values and constants. Further, 17 is a bus line, and 18 is a setting switch for selecting and specifying the transmitter diameter, which is read by a read command signal from the input/output port 19. Further, the table stored in the ROM 12 is not necessarily limited to the above table. Basically, it is sufficient to be able to deal with fluctuations in the commercial power supply frequency between 50Hz and 60Hz, so make span adjustments at 50Hz, and use 55Hz as a reference and adjust the span to a predetermined value so that when it exceeds this, the span becomes 60Hz. It may also be done by multiplying by a coefficient. In this case, ROM1
2 requires a small storage capacity. Although the above-mentioned embodiment realized the present invention using a microcomputer, FIG. 5 shows an embodiment configured for switching between 50Hz and 60Hz without using a microcomputer, but the same parts as in FIG. They are numbered and shown in FIG. As shown in the figure, the frequency of the commercial power supply 8 is counted by a counter 15 and the frequency of the commercial power supply 8 is counted by a D/A converter 2.
After being converted to an analog signal at 0, comparator 2
1 is supplied to one input terminal of 1. Since the reference voltage Vref is supplied to the other input terminal of the comparator 21, its output swings positive or negative depending on the output of the D/A converter 20, that is, the frequency of the commercial power supply 8. The switches 22a and 22b are turned ON and OFF alternately according to the output of the comparator 21 to select the feedback resistors Rf ₁ and Rf ₂ of the operational amplifier 23. At this time, the actually measured flow rate value Vs is supplied to the input side of the operational amplifier 23, and its output side is connected to the base of the voltage/current conversion transistor Tr. Thus feedback resistance
Since the gain of the operational amplifier 23 is determined by selecting either Rf ₁ or Rf ₂ , the actual flow rate value Vs
can be corrected in the same manner as in the above embodiment. Note that the reference voltage Vref in this example is set to be the same as the output of the D/A converter 20 at 55 Hz. Further, in this example, the operational amplifier 23 has two types of gain, but if a feedback resistor is further connected in parallel and one of them is selected by a window comparator, a circuit similar to that of the previous example can be obtained. As specifically explained above with the examples,
According to the present invention, it is possible to eliminate the influence of span fluctuations due to frequency fluctuations of commercial power supply, and a single electromagnetic flowmeter can
Not only can it be used in common for 50Hz and 60Hz, but it can also eliminate the influence of frequency fluctuations around these on the measured values.