JP2562078B2 - Combined flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a flow sensor (also called a micro flow sensor) for measuring a low flow rate range and a flow rate of a Kalman flow meter or the like that is comfortable for measuring a high flow rate range. More particularly, the present invention relates to a combined flow meter having a failure diagnosis function of its flow sensor.

[Conventional technology]

Conventionally, as a composite type flow meter, for example, a flow sensor for measuring a low flow rate range and a Kalman flow meter for measuring a large flow rate range are provided, and a flow rate signal from these flow sensor and flow rate meter is referred to as a microcomputer (hereinafter referred to as a microcomputer). ), There is a gas meter that measures the flow rate.

In this case, the flow sensor is composed of, for example, a heater for heat generation on a silicon base and upstream and downstream temperature-sensitive resistors independently arranged on both sides of the heater, and when the heater is turned on, the flow sensor is measured. Utilizing the fact that the upstream temperature-sensitive resistor is cooled and its resistance value decreases when there is a gas flow, whereas the downstream temperature-sensitive resistor is heated and its resistance value increases, and the difference is proportional to the flow rate. It has characteristics.

On the other hand, the microcomputer inputs a pulse signal obtained by converting the output of the flow sensor into a digital signal, and outputs a pulse output P ₁ when the heating heater of the flow sensor is turned off and a pulse output P ₂ when the heater is turned on. read, the difference P ₂ -P ₁
Is calculated and recognized as a flow rate signal.
Here, the P ₁ has a certain allowable range of the number of output pulses, and a certain value (for example, the temperature-sensitive resistance of the flow sensor, the fixed resistance of the detection unit, and the offset voltage of the differential amplifier is considered (for example,
It is adjusted to be 360 pulses).

[Problems to be Solved by the Invention]

However, in such a conventional combined flowmeter, when the temperature-sensitive resistance that constitutes the flow sensor, the fixed resistance of the detection unit, and the offset voltage of the differential amplifier become large, when the heating heater of the flow sensor is turned off. The pulse output P ₁ may exceed the pulse range, and an accurate flow rate cannot be obtained. In addition, the heat generation heater and the temperature-sensitive resistor of the flow sensor do not have a short mode, but they may be open, that is, broken, and when it becomes open, the output signal of the flow sensor becomes undefined and its original function is no longer fulfilled. There was a problem.

The present invention has been made in view of such circumstances, and an object thereof is to provide a composite flowmeter capable of easily determining the state of a flow sensor failure and failure diagnosis.

[Means for achieving the task]

In order to achieve the above-mentioned object, a composite flow meter according to the present invention comprises a heating heater on a base and upstream and downstream temperature-sensitive resistors independently arranged on both sides of the heater to provide a low flow rate range. A flow sensor to measure, a flow meter to measure a large flow rate, and flow signals from these flow sensors and flow meters are input, and the output signal when the heating heater is turned on is output from the output signal when the heating heater is turned on. The microcomputer is provided with a microcomputer for performing an arithmetic process in which an output value obtained by subtracting a signal is proportional to a flow rate and for diagnosing a failure of the flow sensor.

At this time, the microcomputer, in order to diagnose the failure of the flow sensor, outputs an abnormal signal when the output signal when the heating heater of the flow sensor is turned off exceeds the allowable range regardless of the flow rate. , Or when there is a flow rate signal from the flowmeter and the output signal from the flow sensor is 0 when the heating heater is off and when the heating heater is on, the upstream temperature sensing It shall be judged as a disconnection failure of the resistance.

Further, the microcomputer has no flow rate signal from the flow meter, and the output signal from the flow sensor exceeds the allowable value when the heating heater is turned off and when the heating heater is turned on. When the flow rate signal from the flow meter is present, the output signal from the flow sensor and the output signal when the heater is turned off are When the output signals are the same when turned off, it is determined that the heating heater has a disconnection failure.

[Action]

In the present invention, by inputting the flow rate signal of the flow sensor and the flow rate signal of the flow meter to the microcomputer and comparing these two signals, the failure mode peculiar to the flow sensor can be accurately determined.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a basic block configuration diagram of a composite type flow meter according to an embodiment of the present invention, and FIGS. 2 and 3 show a heater drive circuit of the flow sensor of FIG. 1 and signals of the flow sensor. This figure shows the interface circuit that is input to the microcomputer, and here it is applied to a gas meter. In FIG. 1, 1 is a flow sensor arranged upstream of the gas flow path 4 to measure a low flow rate region of, for example, 150 / h or less, and 2 is close to the flow sensor 1 in the flow path 4. The Kalman flowmeter 3 for measuring a large flow rate region of, for example, 150 / h or more is a microcomputer to which the flow rate signals from the flow sensor 1 and the Kalman flowmeter 2 are input. Based on these signals, the flow rate measurement calculation processing is performed, and the failure diagnosis of the flow sensor 1 is performed.

At this time, as in the conventional example, the flow sensor 1 is composed of a heater for heat generation on a base made of silicon or the like, and upstream and downstream temperature-sensitive resistors independently arranged on both sides of the heater.
Then, as shown in FIG. 2, the heater 11 includes a voltage source 12
Is heated to a predetermined temperature by a constant current supplied from the switch 13 through the switch 13. Also, upstream and downstream temperature sensing resistance
As shown in FIG. 3, reference numerals 21, 22 are connected to the respective sides of the bridge circuit 20 including the fixed resistors 23 and 24, and the differential voltage generated between the detection points ab is detected by the differential amplifier 25. After amplification, it is converted to a digital signal by the A / D converter 26,
A pulse signal proportional to the flow rate is input to the microcomputer 3.

Further, the microcomputer 3 uses the heating heater 11 of the flow sensor 1
The pulse output P ₁ when the switch is off (switch 13 is open) and the pulse output P ₂ when the heater 11 is on (switch 13 is closed) are read, and the difference P ₂ -P ₁ is calculated to calculate the flow rate signal. Recognize as. Here, the pulse output P ₁ has a range of a certain number of output pulses, for example, 0 to 640 pulses, and similarly P ₂ has, for example, 0 to 1390 pulses. The offset voltages of 23 and 24 and the differential amplifier 25 are adjusted to have a certain value (for example, 360 pulses). Note that V _{B in} FIG. 3 represents the voltage of the driving power supply.

By the way, conventionally, when the change in the offset voltage of the upstream and downstream temperature-sensitive resistors 21 and 22, the fixed resistors 23 and 24, and the differential amplifier 25 which constitute the flow sensor 1 becomes large, the output P ₁ thereof exceeds the pulse range. There is a fear that an accurate flow rate cannot be obtained. In addition, the heat generating heater 11 of the flow sensor 1,
The upstream and downstream temperature-sensitive resistors 21 and 22 have no short mode, but may be in an open state. Therefore, when the upstream temperature-sensitive resistor 21 is opened, the outputs P ₁ and P ₂ of the flow sensor 1 are always 0 (zero), and therefore 0 even if there is a flow. When the downstream temperature-sensitive resistor 22 is opened, the output P ₁ of the flow sensor 1 becomes maximum 640 pulses, the output P ₂ becomes 1390 pulses, and the difference P ₂ −P ₁ becomes 750 pulses, and the flow Flow rate signal is output even without. Further, when the heating heater 11 is opened, each pulse output P ₁
In P and P ₂ , P ₁ = P ₂ regardless of the presence or absence of the flow, and there was a problem that the flow rate signal became 0.

However, the present invention is designed to easily determine the failure state of such a flow sensor. That is, in the present embodiment, in the configuration of FIG. 1 to FIG.
The output P _{1 of the} upstream and downstream temperature-sensitive resistors 21 and 22 and the fixed resistors 23 and 24 of the flow sensor 1 and the offset drift of the differential amplifier 25 are set to a preset initial value (for example, 360 pulses). When the value changes from the above, the microcomputer 3 monitors the P ₁ so that when it exceeds a certain operating range, the alarm A is output before the failure.

Further, when there is a flow rate signal from the Kalman flowmeter 2 and the outputs P ₁ and P _{2 of the} flow sensor 1 are both 0 (output over), the microcomputer 3 issues an alarm as an open failure of the upstream temperature-sensitive resistor 21. It is supposed to be issued. At this time,
The alarm A is reset.

Further, when there is no flow rate signal from the Kalman flow meter 2 and the output P ₁ of the flow sensor ₁ exceeds the allowable value of, for example, 640 pulses and the output P ₂ exceeds 1390 pulses (when the output is over). ), An alarm is issued as the downstream temperature-sensitive resistor 22 is opened. At this time also, the alarm A is reset.

Further, the microcomputer 3 outputs each output P _{1 of the} flow sensor 1 in spite of the flow rate signal from the Kalman flow meter 2.
When P ₁ and P ₂ are P ₁ = P _2, an alarm is issued as an open failure of the heating heater 11.

Thus, according to such an embodiment, the flow sensor 1
It has the advantages that the failure and failure prediction of can be correctly diagnosed, the repair location on the gas meter can be clarified, and the repair speed can be increased.

Although the Kalman flow meter was used for the measurement of the large flow rate region in the present invention, a fluidic flow meter, a flow sensor for a large flow rate, or the like can be used instead.

〔The invention's effect〕

As described above, according to the present invention, the flow rate signals from the flow sensor for measuring the low flow rate region and the flow rate meter for measuring the large flow rate region are input, and the heating heater is determined from the output signal when the heating heater is turned on. In a combined flowmeter equipped with a microcomputer that performs an arithmetic process in which the output value obtained by subtracting the output signal when it is turned off is proportional to the flow rate, the failure and state of the flow sensor are diagnosed. The failure mode can be accurately determined. This allows the operating state of the flow sensor to be clearly seen. This is particularly effective in clarifying the repair points on the maintenance of the gas meter and speeding up the repair.

[Brief description of drawings]

FIG. 1 is a basic block diagram showing an embodiment of a composite type flow meter according to the present invention, FIG. 2 is a heater driving circuit diagram of the flow sensor of FIG. 1, and FIG. 3 shows signals of the flow sensor. It is an interface circuit diagram which inputs into a microcomputer. 1 ... Flow sensor, 2 ... Kalman flowmeter, 3 ... Microcomputer, 4 ... Gas flow path, 11
...... Heating heater, 12 ...... Voltage source, 13 ...... Switch, 21 ...
… Upstream temperature resistance, 22 …… Downstream temperature resistance, 23,24 ……
Fixed resistance, 25 …… differential amplifier, 26 …… A / D converter.

Claims (5)

(57) [Claims] 1. A flow sensor for measuring a low flow rate region comprising a heating heater and upstream and downstream temperature-sensitive resistors independently arranged on both sides of the heater on a base, and a flow meter for measuring a large flow rate region. And input the flow signal from these flow sensor and flow meter,
A microcomputer that performs an arithmetic process in which an output value obtained by subtracting an output signal when the heating heater is turned off from an output signal when the heating heater is turned on is proportional to a flow rate, and performs a failure diagnosis of the flow sensor, A composite type flow meter characterized by being equipped with. 2. The microcomputer according to claim 1, further comprising means for outputting an abnormal signal when the output value when the heat generating heater of the flow sensor is turned off exceeds the allowable range regardless of the flow rate. Characteristic compound type flow meter. 3. The microcomputer according to claim 1, wherein the microcomputer has a flow rate signal from the flow meter, and the output signal from the flow sensor is an output signal when the heating heater is turned off and when the heating heater is turned on. When the output signal of 0 is zero, the composite type flow meter is provided with a means for judging a disconnection failure of the upstream temperature-sensitive resistor. 4. The microcomputer according to claim 1, wherein there is no flow rate signal from the flow meter, and the output signal from the flow sensor is the output signal when the heating heater is off and the heating signal when the heating heater is on. A composite type flow meter, comprising means for determining a disconnection failure of a downstream temperature-sensitive resistor when the output signals exceed respective allowable values. 5. The microcomputer according to claim 1, wherein when there is a flow rate signal from the flow meter, the output signal from the flow sensor is the output signal when the heating heater is off and the output signal when the heater is off. A composite type flow meter, characterized in that it has means for judging that the heating heater has a disconnection failure when the output signals are the same.