JPS6033520Y2 - Signal converter zero point display device - Google Patents

Description

[Detailed description of the invention] This invention relates to a zero point display device for a signal converter that is suitable for application to, for example, a signal converter of an electromagnetic flowmeter transmitter, and particularly relates to a signal converter that can easily adjust to the zero point. The present invention aims to provide a zero point display device.

Generally, the output of a transmitter such as an electromagnetic flowmeter transmitter is supplied to a signal converter, which amplifies it, performs calculations to remove the effects of fluctuations in excitation current, etc., and converts it into a signal suitable for transmission and display. converted.

A signal converter is generally constructed as shown in FIG.

In the figure, 1 indicates a signal transmitter. This example shows the case of an electromagnetic flowmeter transmitter, and the flow rate signal e obtained from a pair of electrodes of the electromagnetic flowmeter transmitter 1 is supplied to one input terminal of a differential amplifier 3 constituting a signal converter 2. The input signal e+ is subtracted from the feedback signal ef in the differential amplifier 3 to compensate for the fluctuation component of the excitation current of the oscillator 1, and the input signal e+ is synchronously rectified with a signal in phase with the excitation current in the synchronous rectifier circuit 4. A DC voltage proportional to the flow rate is obtained from the output, and this DC voltage is converted into a pulse signal by a voltage-frequency conversion circuit 5.

The repetition frequency of this pulse signal is proportional to the flow rate, and when the flow rate is 0
When changing ~100%, the repetition frequency is e.g. 0~10K
It is made to change between Hz.

This pulse signal is sent to the frequency-current conversion circuit 6 to reduce the flow rate to 0.
Current output corresponding to ~100% change e.g. 4~20r
'rIA, output to the output terminal 7, and transmitted to a remote point as required.

Further, the pulse signal is led out to the pulse output terminal 9 via the scaler circuit 8 as necessary, and further supplied to the feedback calculation circuit 10, and is proportional to the product of the duty cycle of this pulse signal and the excitation current signal e. It operates to obtain a feedback signal e, and to remove the fluctuation component of the excitation current contained in the flow rate signal e, as described above, using this feedback signal ef-.

In the signal converter 2 configured in this way, the zero point display device includes a neon lamp 11 and a neon lamp 11.
The neon lamp 11 is configured to include a drive circuit 12 that drives the neon lamp 11 to light up using a pulse signal, and a pulse signal obtained from the voltage-frequency conversion circuit 5 is given to this drive circuit 12, and the neon lamp 11 is blinked at the repetition frequency of this pulse signal. A zero point adjustment mechanism 13 provided in the input circuit supplies a part of the excitation current signal er to one of the input terminals of the differential amplifier 3 as a flow rate signal e, and a zero point adjustment signal e2 having the opposite polarity or the same polarity. and the magnitude of this signal e2 is set by the adjustment mechanism 13.
By adjusting the flow rate signal e, the level of the flow rate signal e can be equivalently varied, and the zero point can be shifted.

Therefore, conventionally, the zero point is adjusted by adjusting the zero point adjustment mechanism 13 so that the blinking period of the neon lamp 11 is the longest.

In this case, the blinking period can be adjusted to 10 Hz or less with the naked eye, and the zero point accuracy of the converter 2 can be adjusted to within 0.1%.

However, the conventional zero point display device has the following drawbacks.

(1) When an input with a polarity opposite to the normal input is given to the converter 2, the output voltage of the synchronous rectifier circuit 4 becomes a positive voltage, for example, which is the opposite of normal, and the voltage-frequency converter 5 stops operating.
For example, if the zero point of the converter 2 has shifted to the opposite side, the pulse signal will no longer be output, so the neon lamp 11 will not blink. I can't tell if it's there or not.

(2) Even if the zero point of the converter deviates to the normal side, in order to know the amount of deviation, it is necessary to measure the blinking period of the neon lamp 11, which requires an additional measuring device.

Furthermore, since the amount of deviation is not displayed, it is not clear whether the zero point adjustment has been made accurately.

(3) The blinking of the neon lamp 11 is difficult to discern in a place with a large amount of surrounding light.

(4) If the zero point is shifted to the opposite side of normal, no pulse signal is output, so the differential amplifier 3 receives a feedback signal er.
is no longer given, and a state of saturation occurs.

Even if the zero point is shifted to the normal side in this state, the feedback loop does not close immediately, so the neon lamp 11 does not start blinking.

Therefore, when the zero point adjustment mechanism 13 is operated, the neon lamp 11
The disadvantage is that there is a time delay in the display and adjustment is difficult.

The purpose of this invention is to eliminate these drawbacks, to provide a zero point display device for this type of converter that is easy to adjust and allows direct reading and display of the amount of deviation from the zero point.

An embodiment of this proposal will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of this invention, and parts corresponding to those in FIG. e
, and 15 are input terminals for the excitation current signal er of the electromagnetic flowmeter transmitter.

3 is a differential amplifier, 4 is a synchronous rectifier circuit, 5 is a voltage-frequency conversion circuit, 6 is a first frequency-current conversion circuit, 7 is a current output terminal, 8 is a scaler circuit, 9 is a pulse output terminal, 10
1 is a feedback calculation circuit, and 13 is a zero point adjustment mechanism.

In this invention, the output current sent from the current output terminal 7 is sent through a parallel circuit of a shunt resistor 16 and an ammeter 17, and the output current value is displayed by the ammeter 17. switch S1. S
2, it can be connected to the output side of the second frequency-current conversion circuit 6', and the zero point can be set with the ammeter 17 connected to the output side of the second frequency-current conversion circuit 6'. It is meant to be adjusted.

That is, the second frequency-current conversion circuit 6' converts the frequency of the output pulse of the voltage-frequency conversion circuit 5 into a current.

Specifically, in the first frequency-current conversion circuit 6, the flow rate is 0 to
The frequency O~l0KH2 corresponding to 100% is 4~20r
rIA, whereas the second conversion circuit 6' converts O
Convert ~500H2 to O~1.6rrIA.

The ammeter 17 normally indicates the output current of the first frequency-current conversion circuit 6 using the shunt resistor 16, but when adjusting the zero point, the second frequency-current conversion is performed using the changeover switch S and S2. Indicates the output current of circuit 6'.

For example, the ammeter 17 indicates 0.4 to 2.0 mA from 0 to 100%.
It is marked on the scale.

On the other hand, the input side of the differential amplifier 3 is provided with a bias setting means 18 for shifting the zero point by a certain amount to the normal input side, and the bias signal of the bias setting means 18 is transferred to the switch S□.
, S2 is connected to the input of the differential amplifier 3 by a switch S3.

In this example, this bias setting means 18 is connected to the zero point adjustment mechanism 1.
By switching the switches S1 to S3 inserted in parallel with 3, the ammeter 17 is switched and the zero point is set to 2, for example, for the particle quantity signal input.
．． The configuration is such that it is biased in the normal input direction by an amount equivalent to 5%.

The full scale of the ammeter 17 is set to a value twice the shift amount of the bias setting circuit 18.

Therefore, with this configuration, when the flow rate signal e is zero, the ammeter 17 is connected to the output side of the second frequency-current conversion circuit 6' by switching the switches S1 to S3. As a result, the input of the differential amplifier 3 is biased toward the normal input side by an amount equivalent to, for example, 2.5% of the 100% flow rate.

If the zero point is adjusted accurately by this, the ammeter 17
The instruction indicates the center 50%, and whether the zero point has shifted to the normal input side or to the opposite side of normal can be read by the amount of shift around 50%.

In this way, according to the present invention, the input of the converter 2 is shifted by a certain amount to the normal input side by the bias means 18, and the zero point is displayed on the shift level, so it is possible to determine how much the zero point shifts to the normal side or the opposite side. You can directly read and display what is happening.

In addition, when adjusting the zero point, a voltage with normal polarity is always output from the output of the synchronous rectifier circuit 4, and the zero point is adjusted around that voltage, so even if the zero point is moved to the opposite side of normal, the voltage - frequency will change. This has the advantage that the operation of the converter 5 does not stop and the feedback loop does not become open, so that the zero point adjustment work can be easily performed.

However, in the zero point adjustment state, the full scale of the ammeter 17 indicates 5% of the flow rate from 0 to 100%, so the reading accuracy is 2o@, so if you use a general-purpose ammeter of class 25, The zero point display is also 0.125%, and the zero point can be displayed with sufficient accuracy.

As described above, according to the present invention, handling becomes easy, and
It has the feature that zero point adjustment can be carried out accurately, and its effect is extremely large in practical use.

Moreover, although the case where the zero point display device according to this invention is applied to a signal converter of an electromagnetic flowmeter has been described above, it will be easily understood that this invented circuit can be applied to other signal converters as well.

[Brief explanation of drawings]

FIG. 1 is a system diagram illustrating a conventional zero point display device for a signal converter, and FIG. 2 is a system diagram showing an embodiment of this invention. 13: Zero point adjustment means, 17: Indicator, 18: Bias setting means.

Claims (1)

[Scope of utility model registration request] The signal to be measured from the oscillator is applied, and the fluctuation component of the excitation current of the oscillator is compensated for in the differential amplifier to obtain a DC voltage proportional to the quantity to be measured, and this DC voltage is sent to the voltage frequency converter to be measured. The converted pulse signal is converted into a pulse signal with a repetition frequency proportional to the quantity, and this converted pulse signal is obtained as a current output signal proportional to the quantity to be measured at the output terminal of the first frequency-current conversion circuit, and the voltage-frequency conversion circuit In the signal converter configured such that a part of the output signal of the differential amplifier is fed back to the inverting input terminal of the differential amplifier, the output terminal of the voltage frequency conversion circuit is connected in parallel to the first frequency current conversion circuit. a second frequency-current conversion circuit connected to the output terminal of the signal converter; an indicator that can be selectively connected to the output terminal of the first or second frequency-current conversion circuit; bias setting means connected in a selectively switchable manner in correspondence with the switching connection of the indicator between an input terminal and an inverting input terminal of the differential amplifier; and a bias setting means connected in parallel to the bias setting means. When adjusting the zero point, the indicator is switched to the output terminal of the second frequency-current conversion circuit, and the bias setting means sets a bias of a constant value with the same polarity as the normal input signal under test. is applied to the inverting input terminal of the differential amplifier, the center position of the scale of the indicator is set to the zero point, and when the signal under test is measured, the indicator is switched and connected to the output terminal of the first frequency-current conversion circuit. A zero point display device for a signal converter configured to obtain a current output signal.