JPH04340423A - Electromagnetic flowmeter converter - Google Patents

Abstract

PURPOSE:To obtain an electromagnetic flowmeter converter which enables a flow rate signal to be detected accurately in an electromagnetic flowmeter. CONSTITUTION:An electromagnetic flowmeter measures a flow rate value from a flow rate signal which is generated an two electrodes placed within a pipe by applying an AC magnetic field to a fluid which flows within the pipe. A comparator 3 which generates a pulse signal in synchronization with a commercial power supply frequency, a delay circuit 6 which delays an output of this comparator 3 by an arbitrary time, a frequency-divider circuit 4 which divides an output of the delay circuit 6 into an even-number segments, and a timing circuit 5 are provided. A direction of excitation current which generates a magnetic field is switched by a frequency-dividing pulse signal from a terminal X and at the same time a flow rate signal is sampled by a sampling pulse signal which is output from terminals Y and Z immediately before switching this frequency-dividing pulse signal. As a result, even if noise in synchronization with a power supply is superposed on the flow rate signal, influence of noise can be eliminated and an accurate detection of the flow rate signal can be made since the flow rate signal can be sampled by a sampling pulse which is delayed an arbitrary time from this power supply noise.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an electromagnetic device that generates a switching pulse signal that switches the direction of an excitation current that generates a magnetic field that is applied to a fluid, and a pulse signal that samples a flow rate signal that is generated by applying a magnetic field to a fluid. It relates to a flow meter converter.

0002

[Prior Art] Generally, an electromagnetic flowmeter applies an alternating magnetic field to a fluid flowing in a pipe, samples the flow rate signal generated between two electrodes arranged perpendicular to the direction of this magnetic field, and measures the flow rate value. Conventionally, the pulse signal for switching the excitation current that flows through the coil to generate the alternating magnetic field and the pulse signal for sampling the flow rate signal have been generated using a circuit configuration as shown in FIG. There is.

That is, in FIG. 7, 1 is a power supply circuit;
2 is a voltage dividing circuit, 3 is a comparator, 4 is an even number frequency dividing circuit, and 5 is a timing circuit. The commercial frequency signal (AC signal) shown in FIG. 8(a) output from the power supply circuit 1 is divided by the voltage dividing circuit 2, and further outputted by the comparator 3 into a rectangular wave as shown in FIG. 8(b). obtain. One of these rectangular wave signals is directly output to the timing circuit 5, and the other is frequency-divided by an even number by an even number frequency dividing circuit 4 and output to the timing circuit 5. As a result, from the terminal X of the timing circuit 5, the frequency-divided pulse from the even number multiple frequency divider circuit 4 is output as is, as shown in FIG. (d), (
A pulse signal having the timing shown in e) is output. The direction of the excitation current is switched by the pulse signal output from the terminal X of this timing circuit 5, and
Electrodes A,
The flow signal from between B is sampled.

FIG. 9 is a block diagram of an electromagnetic flowmeter that samples flow signals output from two electrodes A and B. That is, when the excitation current is switched by a pulse signal output from the terminal X of the timing circuit 5 and an alternating current magnetic field is applied to the fluid, a flow rate signal is generated from the electrodes A and B. These flow rate signals are amplified by amplifiers 11 and 12, respectively, and applied to a differential amplifier 13. The differential amplifier 13 takes the difference between these flow rate signals and outputs a signal with a waveform as shown in FIG. 10(a) to the next-stage sample-and-hold circuit (signal at point P). Here, the switches S1 and S2 in the sample and hold circuit are opened and closed in synchronization with the pulse signals output from the terminals Y and Z of the timing circuit, and the hatched part in the figure corresponds to the opening and closing timing, and the new switching Executed immediately before the direction of the excitation current is switched by the signal.

[0005] In this way, the flow rate signal output from the differential amplifier 13 is sampled by opening and closing the switches S1 and S2 in the sample and hold circuit, and the sampled flow rate signal is transmitted through the resistor R1, the capacitor C1, and the resistor R2. , a capacitor C2, and are further amplified by amplifiers 14 and 15. As a result, the waveforms of the flow rate signals at points a and b are shown in FIG. 10(b) and
As shown in (c), these signals are transmitted to the differential amplifier 1.
Added to 6. Then, the difference is taken by the differential amplifier 16 to produce the signal shown in (d) (signal at point Q), and the time constant circuit of resistor R3 and capacitor C3 produces the final signal shown in (e). It is output as a flow rate signal (signal at point R). Note that (f) in Figure 10
The flow rate signal waveform at each point shown in ~(i) lags behind the flow rate signal due to the time constant in the time constant circuit consisting of resistor R1 and capacitor C1 and the time constant circuit consisting of resistor R2 and capacitor C2 in the sample and hold circuit. It shows the signal waveforms of each part when this occurs.

[0006]

[Problems to be Solved by the Invention] Conventional electromagnetic flowmeter converters frequency-divide a pulse signal synchronized with the commercial frequency of the power supply and sample the flow rate signal based on the frequency-divided pulse signal. , as shown in FIG. 10(a),
When commercial power supply noise is superimposed on the flow rate signal, (e),
As shown in the flow rate signal output waveform diagram (i), there was a problem in that the output of the flow rate signal fluctuated, making it impossible to accurately detect the flow rate value.

[0007]

[Means for Solving the Problems] In order to solve such problems, the present invention provides an AC synchronous circuit that generates pulses synchronized with the commercial power supply frequency, and a delay circuit that delays the output of the AC synchronous circuit by an arbitrary time. The circuit includes a frequency dividing circuit that divides the output of the delay circuit into an even number.

[0008]

[Operation] The direction of the excitation current that generates a magnetic field in the fluid is switched by the frequency division pulse signal output from the frequency division circuit, and the flow rate indicating the flow rate value of the fluid is determined by the sampling pulse signal immediately before switching to the frequency division pulse signal. A signal is sampled.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. In this figure, the same parts as those in the block diagram of the conventional electromagnetic flowmeter converter shown in FIG. That is, a delay circuit 6 is added to the conventional electromagnetic flowmeter converter, and the phase is delayed from the pulse signal synchronized with the commercial frequency of the power source output from the comparator 3, and the phase is delayed and output directly to the timing circuit 5. Frequency divider circuit 4
A similar delay signal is also output to generate an even-multiply divided pulse signal and output to the timing circuit 5. As a result, from the terminal X of the timing circuit 5, the even-multiply frequency divided pulse signal The pulse signal is directly output as a switching signal for switching the excitation current, and is also output to terminals Y and Z.
, respectively, generate sampling pulse signals, and use these pulse signals to open and close switches S1 and S2 in the sampling and hold circuit at predetermined timings.
, B are sampled.

FIG. 5 is a timing chart showing the relationship between the commercial frequency signal (AC signal) of the power supply, the output signal of the comparator 3, and the delayed output signal of the delay circuit 6. In this example, the delay circuit 6 9 from the output signal of
It outputs a pulse signal with a 0° phase delay.

Next, FIG. 6 shows the phase of the AC signal at the start of sampling when the switches S1 and S2 of the sampling hold circuit are opened and closed, and the variation value (fluctuation width) of the final flow rate signal output from the differential amplifier 16 in FIG. ) is a graph showing the relationship between In addition, 6.25HZ, 12.5HZ in the diagram
, 25.0Hz indicates the frequency of the excitation current switching signal output from the X terminal of the timing circuit 5, and the switching frequency, that is, the sampling frequency is 25Hz,
Moreover, the fluctuation width is the smallest when the phase difference with the AC signal is 135° or 315°, and it is shown that under this condition, the differential amplifier 16 outputs the most stable flow signal with the smallest fluctuation width. has been done.

As described above, the present invention allows the pulse signal outputted from the comparator 3 in synchronization with the AC signal to be delayed by an arbitrary period of time by the delay circuit 6 and output to the even number frequency divider circuit 4 and the timing circuit 5. As a result, the influence of power supply noise superimposed on the flow rate signal can be prevented, and as a result, accurate sampling of the flow rate signal that does not vary due to noise can be performed.

In this embodiment, the delay circuit 6 is used to delay the pulse signal synchronized with the AC signal from the comparator 3, but as shown in FIG. A delay time or a delay phase angle with respect to the AC signal is set in advance, and when the CPU 7 receives the output from the comparator 3, it is delayed by a time corresponding to this delay time or delay phase angle, and then the even number frequency divider circuit 4 is activated. You may also output it to . Further, as shown in FIG. 3, the circuit after the comparator 3, that is, the delay circuit 6,
The functions of the even number frequency dividing circuit 4 and the timing circuit 5 may be implemented by providing a CPU 9. Also,
As shown in FIG. 4, a low-pass filter may be inserted between the voltage dividing circuit 2 and the comparator 3, and the AC signal, which is a sine wave signal, may be delayed and output to the comparator 3.

[0014]

Effects of the Invention As explained above, the present invention provides an AC synchronous circuit that generates pulses synchronized with the commercial power frequency.
Equipped with a delay circuit that delays the output of the C synchronous circuit by an arbitrary time and a frequency divider circuit that divides the output of the delay circuit into even multiples, and generates a magnetic field in the fluid by the frequency-divided pulse signal output from the frequency divider circuit. In addition to switching the direction of the excitation current, the fluid flow rate signal is sampled using the sampling pulse signal immediately before switching to the frequency-divided pulse signal, so even if noise synchronized with the power supply is superimposed on the flow rate signal, this power supply Since the flow rate signal can be sampled with an arbitrary time delay relative to the frequency, the influence of power supply noise is prevented, and therefore the flow rate signal can be accurately detected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an electromagnetic flowmeter converter according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the electromagnetic flowmeter converter.

FIG. 3 is a block diagram showing a third embodiment of the electromagnetic flowmeter converter.

FIG. 4 is a block diagram showing a fourth embodiment of the electromagnetic flowmeter converter.

FIG. 5 is a timing chart of the device of the above embodiment.

FIG. 6 is a graph showing the relationship between the phase of the AC signal at the start of sampling of the flow rate signal and the fluctuation width of the flow rate signal.

FIG. 7 is a block diagram of a conventional electromagnetic flowmeter converter.

FIG. 8 is a timing chart of various parts of a conventional electromagnetic flow meter converter.

FIG. 9 is a block diagram of a conventional electromagnetic flowmeter.

FIG. 10 is a timing chart of each part of a conventional electromagnetic flowmeter.

[Explanation of symbols]

1 Power supply circuit 2 Voltage divider circuit 3 Comparator 4 Even number divider circuit 5 Timing circuit 6 Delay circuit 7,9 CPU 8. Memory 10 Low pass filter

Claims (1)

[Claims] Claim 1: In an electromagnetic flowmeter that applies an alternating magnetic field to a fluid flowing in a pipe and measures the flow rate value from a flow rate signal generated between two electrodes arranged in the pipe, a pulse synchronized with the commercial power frequency is used. an AC synchronous circuit that generates A
a delay circuit that delays the output of the C synchronous circuit by an arbitrary time;
Equipped with a frequency divider circuit that divides the output of the delay circuit into even multiples,
The direction of the excitation current that generates the magnetic field is switched by the frequency division pulse signal output from the frequency division circuit, and the flow rate signal is sampled by the sampling pulse signal immediately before switching to the frequency division pulse signal. An electromagnetic flowmeter converter characterized by: