JPS593688B2 - electromagnetic flowmeter converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is designed to eliminate noise (signal components and
The present invention relates to an electromagnetic flow rate converter that eliminates phase difference noise (hereinafter referred to as 900 noise) and compensates for fluctuations in an excitation magnetic field, and is capable of generating analog signal output and digital output as output.

Conventional electromagnetic flowmeter converters detect 900 noise using a synchronous rectifier S current, remove the 900 noise by feeding back a voltage of the opposite phase, and then eliminate magnetic field fluctuations using a divider circuit to respond to the flow velocity. Only the induced power is obtained. Such conventional devices require a noise removal circuit and a division circuit.
Not only does the circuit configuration become complicated, but the accuracy decreases due to temperature changes in the elements constituting each circuit is not necessarily small.

Furthermore, when performing digital data processing (mechanical processing), since the output of a normal converter is an analog output, it is necessary to perform analog-to-digital conversion once, which also makes the configuration complicated and expensive. Moreover, it is difficult to avoid a decrease in accuracy. In order to eliminate the above-mentioned conventional drawbacks, the present invention mainly uses a 5-comparison type A-D converter such as a successive approximation type or a tracking comparison type, which is composed of at least a comparator and a D-A converter coupled thereto. The present invention provides an electromagnetic flowmeter converter that

To explain the principle of operation and configuration of the present invention below, the output ei from the electromagnetic flowmeter transmitter is ei=es5in(1)
+ eNC0S () (1) 0
It can be hailed.

However, es is a signal component and eN is a 900 noise component. FIG. 1 shows the waveforms of each of these signal components. As is clear from Equation 1 and FIG. 1, the oscillator output ei is a composite wave of es (5eN).

However, if the signal ei is captured at high speed at every certain moment, only the true signal component es can be measured. That is, in the time chart g3π of FIG. 1, if the component of ei is measured at a period of 1, T, .

o Also, since the signal component is a commercial frequency component, it is usually 5
It is 0 or 60 Hz, and since it is a sine wave, if it is measured at a sufficiently high speed compared to the signal component es, it can be regarded as a DC component at that moment.

In the case of a sine wave, the time rate of change is the same at any time, so if the measurement time for the signal component frequency is longer than the required accuracy, the signal can be treated as a direct current and measured with high accuracy.The present invention utilizes such a measurement principle. Next, the comparison type A-D converter used for this measurement will be explained with reference to Fig. 2.-Generally, the measurement time (conversion time) of the comparison type A-D converter is 1001 tsec or less. 2, the input voltage Ea and the feedback voltage of the output Ea' are applied to the comparator 1, and the output and the clock signal from the clock oscillator 2 are as follows. A control logic circuit or counter 3 is provided for controlling the logic of the A-D converter.

The output of the counter 3 is temporarily stored in a register 4 and then converted into an analog signal Eaf by a DA converter 5.
At the end of A-D conversion, the input voltage Ea and the output voltage Ea' are equal. Ea' is expressed as

However, 21, 22...2n are digital weights,
Eref is a reference voltage for DA conversion operation. Accordingly, C
8::,=1self+TY゜゜゜゜゜゜toto Ea=Ea
f75), the input voltage E
It can be seen that division is performed between a and the reference voltage Eref.

FIG. 3 shows an embodiment of the electromagnetic flow meter converter of the present invention using the above-mentioned comparative type converter.

In this figure, the same reference numerals as in FIG. 2 indicate the same parts, and a pre-stage AC amplifier 6 amplifies the minute output Ei of the electromagnetic flowmeter oscillator 7 and applies it to the comparator 1 of the AD converter. Further, the excitation current of the electromagnetic flowmeter is taken out by a current transformer 8 and applied to a control circuit 9 and a rectifier circuit 10. The control circuit 9 adjusts the phase of the excitation current output and π signal component Ef3! C. A point that is shifted by one is detected, and the start of conversion of the comparison type A/D converter is controlled.

The rectifier circuit 10 also outputs a reference voltage Eref of the D-A converter 5.
A voltage proportional to the excitation current is supplied. Since the measurement operation of the A-D converter is not continuous but is sampling, register 4 is used because it is necessary to store the data from the previous sample.
Not necessary for converters. Now, the A/D conversion operation is started with the output signal of the control circuit 9, and the E
After sampling and converting i, the data is stored in register 4
is stored until the next sample of Ei. Therefore, as is clear from the time chart in FIG. 4, the analog output EO of the D/A converter 5 includes only the signal component of Es in the input signal Ei. Also, the reference voltage Eref
is converted into a direct current by rectifying (or sampling and holding) the excitation current, and is divided by the input signal Es as described above. Furthermore, if the input signal of the DA converter is taken out as it is, a digital signal Ed proportional only to the signal component Es can be obtained. The control circuit 9 obtains a pulse p (Fig. 4) synchronized with 900° noise from the excitation current, but a search coil is inserted into the oscillator to generate a pulse p synchronized with the signal component Es by 90° out of phase with respect to the signal component Es. Even if the signal is taken out, if a sample and hold circuit is inserted before the comparator, the conversion speed of the A-D converter does not need to be so high.

As explained above, according to the present invention, it is possible to remove 900° noise, compensate for fluctuations in the excitation field, and obtain analog and digital outputs simultaneously.

[Brief explanation of drawings]

Fig. 1 is an output signal waveform diagram of an electromagnetic flowmeter transmitter, Fig. 2 is a block diagram of a comparison type A-D converter, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4 is its operation. This is an explanatory time chart. 1... Comparator, 2... Clock oscillator, 3... Control logic or counter, 4... Register, 5... D- A
Converter, 6...Pre-stage amplifier, 7...Magnetic flow meter oscillator, 8...Current transformer, 9...
・Control circuit, 10... Rectifier circuit.

Claims (1)

[Claims] 1. An AC signal from an electromagnetic flowmeter transmitter is directly applied to the input of a comparison type A-D converter comprising at least a comparator and a D-A converter, and a voltage proportional to the excitation current of the electromagnetic flowmeter is applied to the An electromagnetic flow rate characterized in that the electromagnetic flow rate is configured to synchronize with the noise component of the signal and cause the A-D converter to perform a conversion operation at a time when the noise component becomes zero by providing it as a reference voltage to the D-A converter. meter converter.