JPH0450512Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The invention is an electromagnetic flowmeter converter that compares and amplifies an input signal with a feedback signal, converts this output into a frequency signal, and converts the frequency signal into a feedback signal. (hereinafter abbreviated as a converter), and particularly relates to an improvement of a converter that ensures compatibility between the span setting of the converter and a detector.

<Prior Art> FIG. 1 is a block diagram showing the configuration of a conventional converter of this type. An input signal e _i corresponding to the flow rate from a detector (not shown) is applied to the input terminal 1 , and this input signal e _i is amplified by the amplifier 2 . The amplification degree of the amplifier 2 can be varied, and a meter constant is set to compensate for variations in the detector. The deviation between the output of the amplifier 2 and the feedback signal e _f of the multiplier 3 is amplified by the deviation amplifier 4 .
The output of the deviation amplifier 4 is synchronously rectified by a synchronous rectifier circuit 5 and converted into a DC voltage. This DC voltage is converted by a frequency conversion circuit 6 into a frequency corresponding to the DC voltage. This frequency is converted into a direct current by the current conversion circuit 7 and outputted to the output terminal 8, and simultaneously supplied to the frequency ratio conversion circuit 9. The frequency ratio conversion circuit 9 adjusts the frequency ratio of input signals, and by changing this ratio, the span of the converter can be adjusted. The frequency ratio conversion circuit 9 is comprised of a delay circuit, a frequency ratio selection switch, a counter, a gate, etc. as described in, for example, Japanese Patent Publication No. 56-41944 "Signal Converter". The frequency output of the frequency ratio conversion circuit 9 is supplied to the multiplier 3. A comparison signal e _r proportional to the excitation current of the detector is applied to the multiplier 3 from a terminal 10 . The multiplier 3 is composed of, for example, a switch element whose opening and closing are controlled by the frequency output of the frequency ratio conversion circuit 9, and outputs a feedback signal e _f proportional to the product of the comparison signal e _r and this frequency output.

Next, the operation of the converter shown in FIG. 1 constructed as above will be explained. When the input frequency of the frequency ratio conversion circuit 9 is F _i and the output frequency is F _p , F _p =KF _i where k is the frequency division ratio. Since the comparison signal e _r is sampled by the output frequency F _p in the multiplier 3, the feedback signal e _f becomes e _f =F _p e _r =KF _i e _r (1). On the other hand, if m _f is the variation in signal voltage corresponding to the flow rate of the detector, that is, the meter constant, then
The coefficient 1/m _f for correcting this variation is the amplifier 2
Therefore, the output of amplifier 2 becomes e _i /m _f .

Since the entire loop is configured so that the output e _i /m _f of amplifier 2 and the feedback signal e _f match, e _i /m _f = e _f = KF _i e _r (2) ∴ F _i =1 /Km _f・e _i /e _r (3). Frequency F _i and current output at output terminal 8
If the relationship of I _p is I _p = αF _i (α is a conversion constant) (4), then I _p = αI/Km _f ·e _i /e _r (5). Therefore, by setting the frequency division ratio K and the meter constant m _f respectively, the span can be changed while ensuring compatibility between the detector and the converter.

However, the conventional converter shown in FIG. 1 has the following problems.

(1) The structure of the frequency ratio conversion circuit is complicated because it consists of a delay circuit, a gate, and a binary or decimal counter to set the span of the converter. Especially in recent years, as electromagnetic flowmeters have become more accurate, span setting with an accuracy of 0.1% or less is required, so a 4-digit decimal setting circuit is required, and if it is configured with a counter, the span setting circuit will be complicated.

(2) In electromagnetic flowmeters, the magnitude of the output signal from the detector varies slightly from detector to detector. Therefore, in order to prevent span errors from occurring when a detector and converter are combined, a meter constant that indicates the amount of variation in signal voltage at the detector is determined for each detector, and a meter specific to this detector is determined. Although the gain of the first stage amplifier of the converter is adjusted based on a constant, an analog voltage dividing circuit such as a potentiometer is required to adjust the gain of the amplifier 2. For this reason, it is difficult to obtain an accuracy of 0.1% or less.

<Purpose of the invention> In view of the above-mentioned conventional technology, the present invention provides a converter that can set a span with high accuracy and at the same time ensure high accuracy and compatibility with a detector with a simple configuration. The purpose is to

<Configuration of the present invention> The configuration of the present invention to achieve this objective is to compare an input signal with a feedback signal, convert the amplified output into a frequency signal by a frequency conversion circuit, and convert the frequency signal to a feedback signal via a feedback circuit. This electromagnetic flow meter converter is equipped with a digital setting device that divides the frequency signal in the feedback circuit, and the product of the meter constant of the detector and a predetermined full-scale flow rate is set in the digital setting device. That is.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. Note that parts having the same functions as those in the prior art are given the same reference numerals and redundant explanations will be omitted.

FIG. 2 is a block diagram showing one embodiment of the present invention. 11 indicates a digital setting device, and input frequency
Divide F _i according to the set value and output the output frequency F′ _p . The digital setting device 11 is composed of four decimal rate multipliers (RM ₁ to RM ₄ ), and is configured to be able to set the input frequency F _i at a frequency division ratio of four digits (1 to 9999). The division ratio can be set using each multiplier RM ₁ to RM ₄ using the setting switch SW ₁ to RM 4.
SW ₄ is provided to set the numerical values of each decimal digit of 10 ⁴ , 10 ³ , 10 ² , and 10 ¹ , respectively.

Furthermore, in this embodiment, in order to ensure compatibility between the detector and the transducer, values corresponding to the product of a predetermined full-scale flow rate and the meter constant of the detector are set by setting switches SW ₁ to SW ₄ . By doing so, the meter constants are also set digitally at the same time.

FIG. 3 shows waveforms of the input frequency and output frequency of the digital setting device 11. A shows the waveform of the input frequency F _i , and b shows the waveform of the output frequency F′ _p .

For example, if the data input S of a 4-digit rate multiplier is set to S = 1234, the output frequency F' _p will be F' _p = 1234 for the waveform of input frequency F _i of 10000 pulses shown in Figure 3A. This results in a toothless pulse train as shown in Figure 3B. In this way, the output waveform of the rate multiplier becomes a pulse train with missing teeth, so the on/off ratio before and after frequency division decreases in proportion to the number of missing pulses.

In this way, in the embodiment shown in Fig. 2, a simple and inexpensive digital setting device with variable division ratio can be constructed by simply arranging decimal rate multipliers of the required number of digits and setting switches for those digits. .

FIG. 4 is a block diagram showing a second embodiment of the present invention. The configuration shown in FIG _. 4 is such that the output frequency _F'p of the digital setting device 11 in FIG. After converting the pulse train into a pulse train with a constant time width, the multiplier 3 multiplies it by the comparison signal e _r .

In the embodiment shown in FIG. 2, when a rate multiplier is used in the digital setting device 11, the third
As shown in FIG. 4, fluctuations may occur in the output due to irregularities in the output frequency due to missing pulses, but the embodiment shown in FIG. 4 is an attempt to improve this point.

FIG. 5 is a waveform diagram showing the effect of frequency division in FIG. 4. _FIG .
The output frequency _F''p is shown. 1/2 frequency division is shown by B, 1/2 ² frequency division is shown by C, and 1/2 ³ frequency division is shown by D. Gradually as the frequency division ratio increases, It can be seen that the frequency is approaching a constant period.Therefore, by using the frequency divider circuit, the fluctuation of the output is reduced.

<Effect of the invention> As explained above in detail along with the examples,
According to the present invention, a digital setting device is provided in the feedback circuit of the converter to divide the frequency signal, and the product of the meter constant of the detector and the full scale flow rate is set in this digital setting device. It is possible to set the span with high accuracy and at the same time ensure high accuracy and compatibility with the detector with a simple configuration. Furthermore, since there is no need to employ a combination of analog circuits and digital circuits as in the past, the configuration becomes simple.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of a conventional electromagnetic flowmeter converter, Figure 2 is a block diagram showing an embodiment of the present invention, and Figure 3 is the input frequency and output frequency of the digital setting device shown in Figure 2. FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a waveform diagram showing the effect of frequency division in FIG. 4. 2... Amplifier, 3... Multiplier, 4... Deviation amplifier, 5... Synchronous rectifier circuit, 6... Frequency conversion circuit, 9... Frequency ratio conversion circuit, 11... Digital setting device, 12... Minute cycle circuit, 13...Pulse width circuit, e _i ...Input signal, e _r ...Comparison signal, e _f , e' _f ,
e″ _f ...Feedback signal, RM ₁ to RM ₄ ...Rate multiplier, SW ₁ to _{SW 4} ...Setting switch.

Claims (1)

[Claims for Utility Model Registration] (1) Comparing and amplifying an input signal with a feedback signal, converting the amplified output into a frequency signal by a frequency conversion circuit, and converting the frequency signal into the feedback signal via the feedback circuit. In electromagnetic flowmeter converter,
An electromagnetic flowmeter converter characterized in that the feedback circuit is provided with a digital setting device that divides the frequency signal, and a product of a meter constant of a detector and a predetermined full-scale flow velocity is set in the digital setting device. (2) The electromagnetic flowmeter converter according to claim 1, wherein a decimal rate multiplier is used as the digital setting device. (3) The feedback circuit converts the output of the decimal multiplier into the feedback signal via a frequency dividing circuit that converts the output into a pulse train with a substantially constant time width. Electromagnetic flowmeter converter described in ).