JP3636398B2 - Flow meter with reed switch - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow meter including a reed switch as a flow sensor, and a mechanism for suppressing an error from being included in flow measurement based on a detection output of the reed switch due to electrical and magnetic noise and chattering. It is related with the flowmeter provided with.
[0002]
[Prior art]
In a flow meter such as a gas meter, a gas flow rate is measured by driving a mechanical counter based on the expansion and contraction motion of a diaphragm defining a flow chamber formed in a gas passage portion of the meter body. In addition to such a mechanical counter, a gas meter equipped with a microcomputer system includes an electronic counter for notifying a central flow monitoring system of a flow measurement result via a telephone line or the like. As this electronic counter, there is generally known an electronic counter provided with a flow sensor composed of a reed switch that is turned on / off by a rotating magnetic field generated by a magnet attached to a rotating body that rotates according to a gas flow rate. A pulse is output from this flow rate sensor 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]
[Problems to be solved by the invention]
However, the flow rate measurement based on the output of the flow rate sensor composed of the reed switch may be advanced more than the measurement value obtained by the mechanical counter. That is, due to chattering of the reed switch, application of impact to the reed switch, noise intrusion into the pulse input circuit part that captures the output of the reed switch, the output pulse signal of the reed switch has a flow rate based on flow measurement Pulses other than pulses are included. If such a pulse is picked up, a flow rate measurement exceeding the actual flow rate is performed. As a result, the integrated flow rate value of the electronic counter composed of the reed switch becomes larger than the integrated flow rate value of the mechanical counter.
[0004]
FIG. 3A shows an example of the output pulse signal of the read switch. In this signal waveform, the normal flow rate pulse is only (2). Pulses {circle around (1)} and {circle around (3)} appearing before and after the flow rate pulse {circle over (2)} are pulses generated due to chattering of the reed switch. Further, the pulses {circle over (4)} and {circle over (5)} that are generated independently of the flow rate pulse {circle over (2)} are caused by causes such as noise intrusion and impact application.
[0005]
In the conventional electronic counter, as shown in FIG. 3B, the flow rate is measured by determining that all the pulses P whose ON time exceeds, for example, 3 ms are flow rate pulses. For this reason, when the above waveform is obtained, the flow rate pulse for a total of 5 pulses will be obtained.
[0006]
An object of the present invention is to realize a flow meter including a reed switch that can eliminate such an adverse effect.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, in the flowmeter of the present invention, the input circuit portion that captures the output pulse signal of the reed switch has a circuit configuration including C and R so that noise and chattering can be absorbed, and the output pulse signal From this, only the part of the flow rate pulse is identified, extracted, and counted.
[0008]
That is, the present invention provides a flow meter comprising 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 a reed switch that is turned on and off by the rotating magnetic field. ON / OFF of the output pulse signal is detected via a CR circuit having a predetermined time constant, and N times (N is an integer of 2 or more) based on a predetermined sampling pulse signal from the time of detection of the output pulse signal ON. ) When the output pulse signal of the reed switch is sampled continuously and the output pulse signal is detected to be on continuously N times, the reed switch outputs 1 from the reed switch at the time of detecting the off of the output pulse signal. It is determined that the output pulse signal for the number of pulses has been output, and the flow rate is integrated. If on detection of the switch of the output pulse signal is not performed, so that to cancel the on detection of the output pulse signal of the reed switch.
[0009]
In the flowmeter of the present invention configured as described above, the output pulse signal of the reed switch is detected via the CR circuit. Therefore, a pulse caused by chattering of the reed switch, noise intrusion, or the like becomes an output pulse signal. It can suppress getting on.
[0010]
Even if the output pulse signal is detected to be on, if the on state is short, the on detection is cancelled. Therefore, a pulse that appears due to noise intrusion or the like can be ignored. Further, even if the flow rate pulse is temporarily switched off due to noise or the like, such a temporary off state is canceled by the discharge action based on the time constant of the CR circuit, and the off detection is not performed. .
[0011]
As described above, in the present invention, only the flow rate pulse can be detected by ignoring the temporary pulse fluctuation caused by the noise or the like appearing in the output pulse signal.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a gas meter having a reed switch to which the present invention is applied will be described with reference to the drawings.
[0013]
FIG. 1 (A) shows only a circuit portion related to the present invention in a gas meter. Circuit parts other than those shown in the drawing and the mechanical configuration are the same as those of a gas meter that is generally used, and thus the description thereof is omitted.
[0014]
In FIG. 1A, 1 is a reed switch constituting a flow sensor, and 2 is a control circuit constituted by a microcomputer incorporated in a gas meter main body (not shown). The reed switch 1 is opposed to a magnet attached to a rotating body arranged in a gas passage formed in the gas meter body with a partition wall or the like interposed therebetween. Since the rotating body rotates when the gas flows, a rotating magnetic field is generated by the magnet that rotates integrally, and the reed switch 1 is turned on and off as the rotating body rotates.
[0015]
The output S0 of the reed switch 1 is input to an interrupt input port INT2 of the control circuit 2 as an interrupt pulse signal S1 through an input circuit portion 3 having a CR circuit. 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 between the resistors R2 and R3, and is connected in parallel with the reed switch 1. And a pull-up resistor R1 having one end connected at a position between the resistors R2 and R3. The resistor R2 is a resistor for protecting the reed switch 1 and removing noise, and the resistor R3 is a resistor for protecting the input circuit portion of the control circuit 2. The capacitor C1 is a capacitor for reed switch chattering and noise removal.
[0016]
On the other hand, the control circuit 2 includes an output port Pout for outputting a sampling pulse signal S2 that defines a cycle for sampling the output pulse signal S0 of the reed switch 1, and a sampling pulse signal S2 output therefrom. Is input to the interrupt input port INT3 as an interrupt signal.
[0017]
As described above, the control circuit 2 is mainly configured by a microcomputer, and includes 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 this example, on / off detection processing of an output pulse signal as described below is executed based on signals input via the interrupt input ports INT2 and INT3, and only a flow rate pulse is output from the output pulse signal S0. Is used to measure the flow rate.
[0018]
First, the flow pulse output conditions by the reed switch 1 in this example are as follows. A flow pulse waveform P under the following conditions is shown in FIG.
[0019]
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
With reference to the signal waveform of FIG. 2, the on / off detection processing of the output pulse signal of the reed switch will be described. First, when the reed switch 1 is turned on and the 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 point T1). Interrupt processing is started by the fall of the signal S1.
[0020]
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 period of the sampling pulse signal S2 shown in the figure is set to 25 ms, for example. If the signal S1 is held in the on state by two consecutive samplings, it is determined that the reed switch 1 is turned on and the output pulse signal S0 has risen.
[0021]
Thereafter, OFF detection of the reed switch 1 is performed. When the reed switch 1 is turned off and the output pulse signal S0 falls, the interrupt signal S1 rises at a speed defined by the time constant of the CR circuit in the input circuit portion. When this signal S1 rises, for example, by 80%, off detection is performed (time point T4). When ON detection and 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 a corresponding gas flow rate integration process. Thereafter, the detection operations (time points T1A to T3A, time point T1B...) Corresponding to the time points T1, T2, and T3 are repeated.
[0022]
In the example shown in the figure, when the signal waveform B as shown in the next detection cycle at the time points T1A, T2A, and T3A appears, the on-detection of the reed switch 1 is detected twice in succession. Is not made. In this case, the on detection at time T3A is canceled and the next on detection is awaited. For example, by this processing, only pulses having an on period ranging from 17.5 to 30.0 ms or more are valid, and only in that case, on detection is valid.
[0023]
When the signal waveform A as in the section immediately after time T3 appears, even if noise is added to the output pulse signal S0 of the reed switch and the pulse is temporarily turned off, the CR of the input circuit portion Due to the charging of the 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 pulses due to such noise. For example, only a pulse having an off period over a period of 20 ms or more is valid, and only in that case, off detection is valid.
[0024]
In addition, although the above description is an example which applied this invention to the gas meter, of course, it can apply to the flowmeter for measuring fluids other than gas.
[0025]
Further, the sampling period, the number of times of sampling, etc. are not limited to the above example.
[0026]
【The invention's effect】
As described above, in the flowmeter equipped with the reed switch of the present invention, the pulse appearing in the output pulse signal is invalidated due to chattering of the reed switch, intrusion of noise, etc., and only normal flow rate pulses are detected and counted. can do. Therefore, the flow rate can be accurately integrated, and it is possible to avoid the occurrence of a deviation from the integrated value obtained by the mechanical counter as in the prior art.
[Brief description of the drawings]
FIG. 1A is a schematic configuration diagram showing a configuration for detecting a flow rate pulse 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 a reed switch according to the present invention.
FIG. 3 is a signal waveform diagram for explaining adverse effects of a conventional flow meter using a reed switch.
[Explanation of symbols]
1 Reed Switch 2 Control Circuit 3 Input Circuit Portion S0 Reed Switch Output Pulse Signal S1 Interrupt Signal S2 Sampling Pulse Signal

Claims (1)

In a flow meter including 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 that is turned on / off by the rotating magnetic field, on / off of the output pulse signal of the reed switch Is detected through a CR circuit having a predetermined time constant, and the read pulse signal is continuously read N times (N is an integer equal to or greater than 2) based on a predetermined sampling pulse signal from the time when the output pulse signal is detected as ON. When the output pulse signal of the switch is sampled and the ON detection of the output pulse signal is performed N times consecutively, the output pulse signal for one pulse is output from the reed switch at the time of OFF detection of the output pulse signal. Is accumulated, the flow rate is integrated, and the output pulse of the reed switch is continuously generated N times. When the signal on detection is not performed, the flow meter comprising a reed switch, characterized in that to cancel the on detection of the output pulse signal of the reed switch.

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