JPH0738821Y2 - Electromagnetic flow meter - Google Patents

Description

[Detailed Description of the Invention] [Industrial application] The present invention relates to an electromagnetic flowmeter, which is an electromagnetic circuit which is small in size and low in cost by reducing delay elements of a damping circuit which sometimes suppresses fluctuations of a measurement output. It relates to a flow meter.

[Conventional technology]

FIG. 6 is a block diagram showing the configuration of a conventional general electromagnetic flowmeter. In the figure, 1 is a measuring tube through which a fluid to be measured flows, 2 is an exciting coil that is arranged to face the tube 1, and 3a and 3b are perpendicular to the exciting coil 2 while sandwiching the fluid flow. A pair of detection electrodes arranged in the above, and the detector 11 is constituted by the measuring tube 1, the exciting coil 2, and the detection electrodes 3a and 3b. In addition, the exciting coil 2
A rectangular wave alternating current synchronized with a commercial frequency AC (alternating current) power supply is supplied from the exciting current generating circuit 4 as an exciting current, whereby an alternating magnetic field orthogonal to the fluid flow is formed in the measuring tube 1. There is. As a result, in the fluid flowing through the measuring tube 1, super power corresponding to the flow velocity thereof is generated in a direction orthogonal to the alternating magnetic field, and the super power is detected by a pair of detections arranged opposite to the inner wall surface of the measuring tube 1. It is detected by the electrodes 3a and 3b, and this becomes a detection signal according to the flow velocity, that is, a flow rate signal. Then, the flow rate signals from the pair of detection electrodes 3a and 3b are amplified by the AC amplification circuit 5 including the pre-stage amplifiers 5 ₁ and 5 ₂ and the differential amplifier 5 ₃ and input to the sample hold circuits 6 and 7. .

Here, the sample and hold circuits 6 and 7 have resistors 6 ₁ and
The AC amplifying circuit 5 is composed of 7 ₁ , switches 6 ₂ and 7 ₂ which are turned on / off by sampling signals S ₁ and S ₂ , capacitors 6 ₃ and 7 ₃ and buffer amplifiers 6 ₄ and 7 _{4 having} high input impedance. Sampling signals S ₁ and S _{2 obtained} by synchronizing the rectangular wave flow signal shown in FIG.
(See FIGS. 7 (b) and 7 (c)), the output value is further differentially amplified by the differential amplifier 8 and converted into a DC signal. At this time,
As shown in FIG. 7, the sampling timings of the sample and hold circuits 6 and 7 are set so as to be performed at the most stable last stage of the flow rate signal synchronized with the rectangular wave exciting current.

The DC flow signal converted in this way is
By removing the noise contained in the signal that has been damped by the damping circuit 9 consisting of 9 ₁ , capacitor 9 ₂ and amplifier 9 ₃ , it is converted into a current signal by the voltage / current (V / I) converter 10. The current signal is sent to the outside as a measurement output according to the flow rate.

[Problems to be solved by the invention]

By the way, in an electromagnetic flow meter, the measurement output is generally fluctuated due to the commercial frequency noise of the AC power source that enters from around the signal converter and the fluid noise generated between the detection electrodes 3a and 3b of the detector 11. It easily wanders, and the damping circuit 9 is used to suppress this wandering.
However, in order to slow down the response speed of the output, the time constant of the damping circuit 9 must be increased, and as a result, the resistance 9 ₁ and the capacitor 9 ₂ forming the damping circuit 9 are increased.
As a result, it is necessary to have a large resistance value and a large capacitance. For this reason, there is a problem that the cost of the circuit configuration is increased and the space of the printed board is increased.

The present invention has been made in view of these points,
The objective is to provide an electromagnetic flowmeter that reduces the delay element of the damping circuit that suppresses fluctuations in the measurement output and that enables circuit size reduction and cost reduction.

[Means for solving problems]

The electromagnetic flowmeter of the present invention is a detector that detects an electromotive force generated when a magnetic field is applied to a fluid as a flow rate signal, a sample hold circuit that samples and holds the flow rate signal obtained from this detector, and this sample hold circuit. By differentially amplifying the output value of, and including a damping circuit for suppressing the fluctuation of the output, by providing a plurality of sampling time constant circuit section in the sample hold circuit,
The sampling cycle or sampling time and the sampling time constant are switched according to the response speed of the output.

[Action]

In the present invention, the delay element of the damping circuit can be reduced. That is, the damping circuit has a continuous time system response, while the sample hold circuit has a discrete time system response. In addition, the response time of the sample-hold circuit is determined by four factors: resistance value, capacitor capacity, sampling period, and sampling time. Therefore, if these constants are properly selected, the constants smaller than the resistance value and the capacitance of the damping circuit
Similar response speed can be obtained.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

FIG. 1 is a block diagram showing switching of resistance values among switching of sampling time constants in an embodiment of an electromagnetic flow meter according to the present invention. The electromagnetic flowmeter of this embodiment is
The super power obtained between the detection electrodes 3a, 3b of the detector 11 is detected as a flow rate signal, and this flow rate signal is converted into a DC signal via the AC amplification circuit 5, the sample hold circuits 6, 7 and the differential amplifier 8. After that, the signal is passed through the damping circuit 9 to V /
That is configured to convert the current signal in the I converter 10 is similar to that of the conventional example of FIG. 6, the sampling unit constituting one of the sample-and-hold circuit 6, the switch 6 ₂ It formed from on-time to the resistor ₆₁ and the capacitor 6 _3, two sampling time constant circuit portion 6A which is formed from switches 6 ₂ resistance when a on-6 ₁ a and the capacitor 6 _3, provided with a 6B, other sample the sampling unit constituting the hold circuit 7, is formed from the switch 7 resistor when the _second on-7 ₁ and the capacitor 7 _3, switch 7 ₂ a on-time of the resistor ₇₁ a
And two sampling time constant circuit portion 7A is formed from the capacitor 7 _3, provided 7B. Then, the sampling time constant circuits 6A, 6B and 7A, 7B of the sample hold circuits 6 and 7 are selected according to the output response speed, and the resistance values of the sample hold circuits 6 and 7 are switched. It is a thing.

At this time, the resistors 6 ₁ and 7 ₁ of the sample and hold circuits 6 and 7 have the same resistance value R ₁ , and the resistors 6 ₁ a and 7 ₁ a also have the same resistance value R ₂ (R ₂ ≠ R ₁ ).
Have. Further, the capacitors 6 ₃ and 7 ₃ have the same capacitance, and the switches 6 ₂ a and 7 ₂ a are driven by the sampling signals S ₁ and S ₂ similar to the conventional one which drive the switches 6 ₂ and 7 _2. It is said that it is selectively turned on and off. In the figure,
The same reference numerals indicate the same or corresponding parts.

According to the above-described embodiment, the sampling time constant circuit units 6A, 6B and 7A, 7B of the sample hold circuits 6 and 7 are appropriately selected according to the output response speed, and the resistance values of the sample hold circuits 6 and 7 are selected. By switching R ₁ and R ₂ , the response speeds of the sample and hold circuits 6 and 7 can be changed. As a result, the damping circuit 9 can have fewer delay elements than the conventional one. Further, by combining the sample hold circuits 6 and 7 and the damping circuit 9 of the present embodiment, a good output response speed can be created.

FIG. 2 shows switching of capacitor capacity among switching of sampling time constants in the present invention.
This embodiment is different from that of FIG. 1 in that the capacitances of the sample and hold circuits 6 and 7 are switched according to the response speed of the output. Here, the sampling time constant circuit units 6A, 6 of the sample hold circuit 6
B is a series body of a resistor 6 ₁ and a switch 6 ₂ and has capacitors 6 ₃ and 6 ₃ a and switches 6 ₅ and 6 6 having different capacitances.
₅ a structure connected in parallel to each other a series connection body with a, switch
6 ₂ selectively turns on the switch 6 ₅ or 6 ₅ a in synchronization with the operation to turn off the drive. In addition, the sampling time constant circuit units 7A and 7B of the sample hold circuit 7 include a resistor 7 ₁ and a switch 7 ₂
Capacitors with different capacitor capacities with respect to the series body of
7 ₃ and 7 ₃ a and switches 7 ₅ and 7 ₅ a are connected in parallel to each other, and switch 7 ₅ or 7 ₅ a is selectively turned on and off in synchronization with the operation of switch 7 _2. It is supposed to do. Therefore, also in this embodiment, the same effect as that of FIG. 1 is obtained.

FIG. 3 is a diagram for explaining the switching of the sampling cycle in the present invention. In this embodiment, the sample hold circuits 6 and 7 having the same configuration as in FIG. 6 are used. As shown in the figure, the period (T, T
/ 2) two sampling signals S ₁ and S ₁ a different from each other are selectively applied to each sample and hold circuit 6,
The sampling rate of 7 is switched according to the response speed of the output, and the response speed of those sampling circuits is changed.

FIG. 5 is a waveform diagram of the sampling signal for explaining the switching of the sampling time in the present invention. In this embodiment, the sample hold circuits 6 and 7 having the configuration of FIG.
As shown in FIG. 5, the sampling time (t
s, 2ts) two different sampling signals S ₁ and S ₁ b are selectively added respectively, so that the sampling time of each sample and hold circuit 6 and 7 can be changed according to the response speed of the output. And the response speed of those sampling circuits is changed.

In the above-described embodiment, the resistance value, the capacitor capacity, the sampling period, and the sampling time of the sample-hold circuit are shown as two cases, but the present invention is not limited to this. Three or more kinds of switching may be performed for each element, or both the resistance value and the capacitor capacity may be switched.

Further, in the case of an electromagnetic flow meter using a microprocessor, the function of the dampening circuit can be provided by software, but it goes without saying that the present invention can also be applied in this case.

[Effect of device]

As described above, according to the present invention, the delay element of the dipping circuit can be made smaller than before, so that the resistance value and the capacitor capacity used in this damping circuit can be suppressed to a small value, and the cost can be kept low. You can Also, the space of the circuit board can be reduced. Furthermore, even if the output response speed is the same, the larger the delay element of the sampling circuit, the higher the noise attenuation rate, and therefore the effect of improving the noise resistance characteristic is achieved.

[Brief description of drawings]

FIG. 1 is a block diagram showing switching of resistance values among switching of sampling time constants according to an embodiment of the present invention, and FIG. 2 is a block diagram showing switching of capacitor capacitance among switching of sampling time constants according to the present invention. FIG. 3 is a block diagram of the main part for explaining the switching of the sampling cycle in the present invention, FIG. 4 is a waveform diagram of the sampling signal used for the main block diagram of FIG. 3, and FIG. FIG. 6 is a waveform diagram of a sampling signal for explaining switching of sampling time in the invention, FIG. 6 is a block diagram showing a configuration of a conventional general electromagnetic flow meter, and FIG. 7 is sampling by a flow signal and a sample hold circuit in FIG. FIG. 6 is an explanatory diagram showing the timing relationship of FIG. 1 ... Measuring tube, 2 ... Excitation coil, 3a, 3b ... Detection electrodes, 4 ... Excitation current generation circuit, 5 ... AC amplification circuit, 6,
7 …… Sample hold circuit, 6A, 6B, 7A, 7B …… Sampling time constant circuit section, 8 …… Differential amplifier, 9 …… Damping circuit, 11 …… Detector.

Claims (1)

[Scope of utility model registration request] 1. A detector that detects an electromotive force generated when a magnetic field is applied to a fluid as a flow rate signal, a sample hold circuit that samples and holds the flow rate signal obtained from this detector, and an output value of the sample hold circuit. Is provided with a damping circuit that suppresses the fluctuation of the output, and the sampling and holding circuit is provided with a plurality of sampling time constant circuits, so that the sampling time constant and the sampling rate can be adjusted according to the response speed of the output. An electromagnetic flowmeter characterized in that the cycle or the sampling time is switched respectively.