JPS6311662Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal exchange device that is used when measuring a flow rate by receiving a pulse signal from a flowmeter, and converts the pulse signal into a digital measurement value.

As shown in FIG. 1, a conventional signal conversion device of this type receives an input pulse signal P _i from a flowmeter (not shown).
is counted by the pulse counter 1, and at the same time the clock pulse P _c is counted by the clock counter 2, and the count value M _o of the pulse counter 1 and the count value of the clock counter 2 are calculated at each measurement period determined by the output of the timing circuit 6.
T _o is read by input circuit 3, and the read count value
M _o・T _o and pre-given span pulse period T _s
(Clock pulse conversion period of pulse signal input during full span) Measured value calculation circuit 4
Then, the calculation T _s・M _o /T _o is performed to obtain the digital measured value input X _o , and then the following equation is processed by the first-order lag filter 5 at a fixed period ΔT to obtain the measured value output Y _o . There is.

Y _o = Y _o-1 + 1/1 + T/ΔT (X _o − Y _o-1 ) (1) Where, T: Time constant of the filter By the way, the input pulse signal P _i can be given as a flow signal from a flow meter. many. In this case, the oval flowmeter that is commonly used has an elliptical rotor that does not rotate at a constant speed even when a constant flow rate is flowing, so in principle, the pulse period is not evenly spaced. Instead, it becomes a periodic, irregularly spaced pulse. In addition, in flow measurement, there is generally so-called pulsation, and even if the output is output at equal intervals in principle like a turbine flow meter,
This may result in pulses that are periodically spaced at irregular intervals. When such irregularly spaced pulses are converted into digital values by a conventional signal converter, the stable value when the time constant of the filter 5 is increased does not become a correct measured value, but shows a higher value. The deviation is so large that the degree of non-uniform spacing is remarkable. This relationship will be explained below using the time chart of FIG.

In FIG. 2, A is the waveform of the input pulse signal P _i and B is the waveform of the measured value input X _o . Furthermore, the second
In the figure, in order to simplify the explanation, a case is shown in which X _o is calculated every time one pulse of the input pulse signal P _i arrives. As a result of one pulse of flow,
One pulse is transmitted from the flowmeter, and the count value T _o of the clock counter 2 counted during the time from the previous pulse to the current pulse is read by the input circuit 3.
Measured value input X _o is required. That value is held until the next pulse. Moreover, input the measured value
The time that X _o is held does not correspond to the measurement cycle in which the measured value was actually obtained, but is delayed by one pulse. For this reason, the correct retention time will be shorter when the measurement period T _o is small and the measured value input X _o is large, and will be longer when T _o is large and X _o is small, whereas the actual retention time _is It becomes longer when X _o is large, and becomes shorter when T _o is large and X _o is small. Therefore, even if the processing is performed by the first-order lag filter 5 with a constant period ΔT, the stable value when the filter time constant T is increased is the correct stable value as shown by the dotted line in Figure 2 (b). (constant chain line), but shows a higher value. The deviation becomes so large that the degree of non-uniform spacing becomes remarkable, and may not be negligible in terms of measurement.

The present invention is a signal conversion system that can stabilize the measured value even if the pulse signal is periodic and irregularly spaced pulses by setting the processing cycle of the filter based on the measurement cycle of the pulse signal. This is the realization of the device.

FIG. 3 is a connection diagram showing one embodiment of the signal conversion device of the present invention. In FIG. 3, the difference from the conventional example in FIG.
The point is that the gain of the filter 5 is made variable by using T _o and calculating the following equation.

Y _o = Y _o-1 + 1/1 + T/T _o (X _o − Y _o-1 ) (2) In the present invention configured in this way, the measured value input X _o and its retention time are the same as the conventional one. However, when the measurement period T _o becomes smaller and the measured value input X _o becomes larger, the gain of the filter 5 becomes 1/1 + (T/
To compensate for the effect of the holding time becoming longer as T _o ) becomes smaller, and as T _o becomes larger and X _o becomes smaller, the gain of the filter 5 increases,
Compensate for the effects of shorter retention times. As a result, the stable value when the time constant of the filter 5 is increased approaches the correct stable value.

Note that in the above example, the period of the input pulse signal P _i is measured every time one pulse arrives, but P _i
The same method can be used to measure the period (average period) every time a plurality of pulses occur. Further, each process may be performed in synchronization with a fixed period processing signal _Ps as shown in the embodiment of FIG. In this case, the input pulse signal P _i has a low frequency, and when no pulse is input within the measurement period, measurement value calculation and filter processing are not performed. The time chart in FIG. 5 shows this relationship. In FIG. 5, A is the waveform of the input pulse signal P _i , B is the waveform of the fixed-cycle processed signal P _s , C is the timing of input reading, D is the processing timing of the measured value calculation circuit 4 and filter 5, and E is the waveform of the fixed-cycle processed signal P s. This is the waveform of the measured value input _Xo . In other words, the input circuit 3 receives the first input pulse input after the previous processed signal _Ps and the current processed signal.
The values M _o and T _o counted by pulse counter 1 and clock counter 2 are read between the first input pulse input after P _s , and the measured value calculation circuit 4 and filter 5 Processing is performed only when data is read. Note that a microcomputer μp may be used as the input circuit 3, the measured value calculation circuit 4, and the filter 5 surrounded by the dashed line in FIG. 4, and these functions may be realized by a program. In this case, the timing of the operation is controlled by interrupting the microcomputer at the rising edge of the first input pulse P _i after the processed signal P _s .

As explained above, in the present invention, the processing period of the first-order lag filter is set in relation to the period of the input pulse signal, so even if the pulse signal is periodic and irregularly spaced, accurate measurements can be made. A signal conversion device is obtained which can be stabilized at a value.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing an example of the conventional device, Fig. 2 is a time chart for explaining its operation, Fig. 3 is a connection diagram showing an embodiment of the device of the present invention, and Fig. 4 is a connection diagram of the device of the present invention. A connection diagram showing another embodiment, and FIG. 5 is a time chart for explaining its operation. 1... Pulse counter, 2... Clock counter, 3... Input circuit, 4... Measured value calculation circuit, 5
...Filter, 6...Timing circuit.

Claims (1)

[Scope of utility model registration request] a pulse counter for counting input pulses, a clock counter for counting clock pulses, and calculating the input pulse period by reading the counts of the pulse counter and the clock counter for each measurement period;
A measurement value calculation circuit that divides the span pulse period by the input pulse period to obtain a digital measurement value, a first-order lag filter to which the output of this measurement value calculation circuit is added, and a gain of the first-order lag filter that calculates the digital measurement value by dividing the span pulse period by the input pulse period. A signal exchange device characterized by comprising means for setting based on a count value of.