JPH09311060A - Flowmeter provided with reed switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mechanism by which a flow rate can be measured with good accuracy, by preventing an erroneous detection due to the chattering of a reed switch or to the creeping of a noise in a flowmeter which is provided with the reed switch. SOLUTION: In a flowmeter which is provided with a reed switch, the ON/ OFF operation of the output pulse signal S0 of the reed switch is detected via a CR circuit having a prescribed time constant. From a point of time (T1) when the ON operation of an output pulse signal S1 is detected, the output pulse signal S1 is sampled continuously twice on the basis of a predetermined sampling pulse signal S2. When the ON operation is detected continuously twice, it is judged that flow rate pulses covering one pulse are output from the reed switch at a point of time when the OFF operation of the output pulse signal S1 is detected, and a flow rate is integrated. When the ON operation of the output pulse signal S1 is not detected continuously twice, the detection of the ON operation of the output pulse signal S1 is cancelled. Only flow rate pulses are discriminated, and the flow rate can be measured with good accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter having a reed switch as a flow sensor, and an error is included in the flow measurement based on the detection output of the reed switch due to electrical or magnetic noise or chattering. The present invention relates to a flow meter equipped with a mechanism for suppressing the occurrence of the above.

[0002]

2. Description of the Related Art In a flow meter such as a gas meter, a mechanical counter is driven based on the expansion and contraction movement of a diaphragm defining a flow chamber formed in a gas passage portion of a meter body to measure a gas flow rate. There is. In addition to such a mechanical counter, a gas meter equipped with a microcomputer system is provided with an electronic counter for notifying a centralized monitoring system of a flow rate measurement result via a telephone line or the like. As this electronic counter, generally, there is known one provided with a flow rate sensor including a reed switch which is turned on and off by a rotating magnetic field generated by a magnet attached to a rotating body which is rotated by a gas flow rate. This flow sensor outputs a pulse at a constant flow rate, for example, every 0.7 liter. Therefore, on the receiving side, the gas flow rate can be integrated by counting the number of received pulses.

[0003]

However, the flow rate measurement based on the output of the flow rate sensor composed of the reed switch may be over-advanced as compared with the value measured by the mechanical counter. That is, due to chattering of the reed switch, impact application to the reed switch, noise intrusion into the pulse input circuit part that captures the output of the reed switch, etc., the reed switch output pulse signal contains the flow rate based on the flow rate measurement. Pulses other than pulses are included.
If such a pulse is picked up, a flow rate measurement higher than the actual flow rate will be performed. As a result, the integrated value of the flow rate of the electronic counter including the reed switch becomes larger than the integrated value of the flow rate of the mechanical counter.

FIG. 3A shows an example of the output pulse signal of the reed switch. In this signal waveform, there are only normal flow pulses. The pulse appearing before and after this flow rate pulse is a pulse generated due to chattering of the reed switch. Also, the pulse that is generated independently of the flow rate pulse, is noise intrusion,
This is due to the impact application.

In the conventional electronic counter, as shown in FIG. 3 (B), all the pulses P whose on-time exceeds, for example, 3 ms are determined to be flow rate pulses and the flow rate is measured. For this reason, when the above-mentioned waveform is obtained, it is considered that the flow rate pulse for a total of 5 pulses has been obtained.

An object of the present invention is to realize a flow meter equipped with a reed switch capable of eliminating such an adverse effect.

[0007]

In order to solve the above problems, the flowmeter of the present invention includes C and R in order to absorb noise and chattering in the input circuit portion which takes in the output pulse signal of the reed switch. In addition to the circuit configuration, only the flow rate pulse portion is identified from the output pulse signal and taken out for counting.

That is, the present invention provides a flowmeter equipped with a reed switch configured to generate a rotating magnetic field by a passing fluid and measure a flow rate based on an output pulse signal of the reed switch which is turned on and off by the rotating magnetic field, ON / OFF of the output pulse signal of the reed switch is detected via a CR circuit having a predetermined time constant, and N times (N is 2) based on a predetermined sampling pulse signal from the time of detection of ON of the output pulse signal. If the output pulse signal of the reed switch is continuously sampled and the ON detection of the output pulse signal is performed N times consecutively, the read pulse is detected at the time of the OFF detection of the output pulse signal. It is judged that the output pulse signal for one pulse has been output from the switch, the flow rate is integrated, and it continues N times. When said reed switch of the output pulse signal on detection is not performed, so that to cancel the on detection of the output pulse signal of the reed switch Te.

In the flow meter of the present invention thus constructed,
Since the output pulse signal of the reed switch is detected via the CR circuit, it is possible to prevent a pulse caused by chattering of the reed switch, intrusion of noise, or the like from being superimposed on the output pulse signal.

Even if the output pulse signal is detected as ON, if the ON state is short, the ON detection is canceled. Therefore, the pulse that appears due to noise intrusion can be ignored. Furthermore, even if the flow rate pulse is temporarily turned off due to noise or the like, C
Due to the discharge action based on the time constant of the R circuit, such a temporary OFF state is canceled and OFF detection is not performed.

As described above, according to the present invention, only the flow rate pulse can be detected by ignoring the temporary pulse fluctuation caused by noise or the like appearing in the output pulse signal.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A gas meter having a reed switch to which the present invention is applied will be described below with reference to the drawings.

FIG. 1A shows only the circuit portion of the gas meter relevant to the present invention. Circuit parts and mechanical structures other than those shown are the same as those of commonly used gas meters, and therefore their explanations are omitted.

In FIG. 1A, 1 is a reed switch that constitutes a flow sensor, and 2 is a control circuit that is composed of a microcomputer incorporated in a gas meter main body (not shown). Reed switch 1 is
The partition wall and the like are sandwiched between the magnets and the magnets attached to the rotor arranged in the gas passage formed in the gas meter body. Since the rotating body rotates when the gas flows, the rotating magnetic field is generated by the magnet that rotates integrally, and the reed switch 1
Turns on and off as the rotating body rotates.

The output S0 of the reed switch 1 is passed through an input circuit portion 3 having a CR circuit to generate an interrupt pulse signal S.
It becomes 1 and is input to the interrupt input port INT2 of the control circuit 2. The input circuit portion 3 has resistors R2 and R3 connected in series between the reed switch 1 and the input peat INT2 and one end connected to a position between them, and is in parallel connection with the reed switch 1. A pull-up resistor R1 having one end connected between the capacitor C1 and the resistors R2 and R3 is provided. Resistance R2
Is a resistor for protecting the reed switch 1 and for removing noise, and a resistor R3 is a resistor for protecting the input circuit portion of the control circuit 2. The capacitor C1 is a capacitor for chattering and noise removal of the reed switch.

On the other hand, the control circuit 2 is provided with an output port Pout for outputting a sampling pulse signal S2 defining a cycle for sampling the output pulse signal S0 of the reed switch 1, and the sampling output from the output port Pout. The pulse signal S2 is input to the interrupt input port INT3 as an interrupt signal.

The control circuit 2 is mainly composed of a microcomputer as described above, and is provided with a storage unit such as a ROM storing a control program and a RAM used as a work area. In the control circuit 2 of the present example, on / off detection processing of the output pulse signal as described below is executed based on the signals input via the interrupt input ports INT2 and INT3, and only the flow pulse from the output pulse signal S0 is executed. Is identified and the flow rate is measured.

First, the output condition of the flow rate pulse by the reed switch 1 in this example is as follows. A flow rate pulse waveform P under the following conditions is shown in FIG.

Flow rate per pulse: 0.35 liters Pulse period: 125 ms (= 8 Hz) (10.08 m ³ / h) Duty ratio: 7: ^{3 to 3} : 7 Minimum on-time width: 37 ms Minimum off-time width: 37 ms The on / off detection processing of the output pulse signal of the reed switch will be described with reference to the signal waveform of FIG. First, when the reed switch 1 is turned on and its output pulse signal S0 rises, the interrupt signal S1 supplied to the interrupt input port INT2 of the control circuit 2 via the input circuit portion 3 falls (time T1). Interrupt processing is started by the fall of the signal S1.

That is, after this time T1, the sampling pulse signal S2 input to the interrupt input port INT3 is read, and the signal S1 is sampled at the rising times T2 and T3. The cycle of the illustrated sampling pulse signal S2 is set to 25 ms, for example. The signal S is obtained by sampling two consecutive times.
When 1 is held in the ON state, it is determined that the reed switch 1 is switched to the ON state and the output pulse signal S0 has risen.

After that, the reed switch 1 is detected to be off. Reed switch 1 turns off and output pulse signal S
When 0 falls, the interrupt signal S1 rises at a speed defined by the time constant of the CR circuit of the input circuit portion. When this signal S1 rises by, for example, 80%, off detection is performed (time point T4). When the ON detection and the OFF detection are performed in this way, the control circuit 2 determines that one pulse of the flow rate pulse P has been output, and performs the corresponding gas flow rate integration processing. Thereafter, the detection operation (time points T1A to T3A, time point T1B ...) Corresponding to the time points T1, T2, T3 is repeated.

In the illustrated example, when the signal waveform B appears in the section of the next detection cycle, that is, the time points T1A, T2A and T3A, the reed switch 1 is detected to be ON twice and then continuously. ON is not detected. In this case, the ON detection at the time point T3A is canceled and the next ON detection is awaited. For example,
By this processing, only the pulse having the ON period of 17.5 to 30.0 ms or more is valid, and only in that case, the ON detection is valid.

When the signal waveform A appears in the section immediately after the time point T3, even if noise is added to the output pulse signal S0 of the reed switch and the pulse is temporarily turned off, the input circuit is turned off. Due to the charging of the partial CR circuit, a response delay occurs at the rising edge of the signal S1.
Therefore, if the time constant of the CR circuit is set appropriately, it is possible to avoid picking up a pulse due to such noise. For example, only a pulse having an off period extending over a period of 20 ms or more is valid, and only in that case, the off detection is valid.

Although the above description is an example in which the present invention is applied to a gas meter, it goes without saying that the present invention can also be applied to a flow meter for measuring a fluid other than gas.

The sampling period, the number of times of sampling, etc. are not limited to the above example.

[0026]

As described above, in the flowmeter equipped with the reed switch of the present invention, the pulse appearing in the output pulse signal thereof is invalidated due to chattering of the reed switch, intrusion of the noise, etc., and only the normal flow rate pulse is obtained. Can be detected and counted. Therefore, the flow rate can be accurately integrated, and it is possible to avoid the occurrence of a deviation from the integrated value by the mechanical counter as in the conventional case.

[Brief description of drawings]

FIG. 1A is a schematic configuration diagram showing a configuration for flow rate pulse detection in a gas meter equipped with a reed switch to which the present invention is applied, and FIG. 1B is a signal waveform diagram showing a normal flow rate pulse.

FIG. 2 is a signal waveform diagram for explaining an on / off detection operation of the reed switch according to the present invention.

FIG. 3 is a signal waveform diagram for explaining an adverse effect in a flow meter using a conventional reed switch.

[Explanation of symbols]

 1 reed switch 2 control circuit 3 input circuit part S0 reed switch output pulse signal S1 interrupt signal S2 sampling pulse signal

Claims (1)

[Claims] 1. A rotating magnetic field is generated by a passing fluid,
In a flowmeter equipped with a reed switch configured to measure a flow rate based on an output pulse signal of the reed switch which is turned on and off by the rotating magnetic field, a CR circuit having a predetermined time constant for turning on and off the output pulse signal of the reed switch. Via the output pulse signal, the output pulse signal of the reed switch is continuously sampled N times (N is an integer of 2 or more) continuously based on a predetermined sampling pulse signal from the time when the output pulse signal is detected to be ON. When the ON detection of the output pulse signal is performed N times consecutively, it is determined that the output pulse signal for one pulse is output from the reed switch at the time of the OFF detection of the output pulse signal. When the flow rate is integrated and the output pulse signal of the reed switch is not detected to be ON continuously N times, Flowmeter having a reed switch, characterized in that to cancel the on detection of the output pulse signal of the reed switch.