JPH06341880A - Thermal type mass flow rate control device - Google Patents

Abstract

PURPOSE:To provide a thermal type mass flow rate control device which can detect a backward flow and an excessive flow automatically. CONSTITUTION:The output of a bridge circuit 7 consisting of thermo resistors 6a and 6b constituting a mass flow signal detection means is amplified by a differential amplifier 8 to obtain a mass flow signal B. A mass flow signal B is input to a backward flow signal detection comparison circuit 14 which compares it with a backward flow detection setting signal (-2%) C to detect the presence or absence of backward flow. Also, the mass flow signal B is input to an excessive flow detection comparison circuit 15 which compares it with an excessive flow detection setting signal (100%) A to detect the presence or absence of the amount of excessive flow. The output of the comparison circuit 14 or 15 is subjected to waveform shaping by a Schmitt circuit, is supplied to a drive circuit 18. When an abnormality is detected, an alarm actuation relay 20 is driven and a display LED lamp 19 is lit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection device which is suitable for a thermal mass flow controller and which detects backflow and overflow.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an example of a conventional thermal mass flow controller. The thermal mass flow controller 1 includes a sensor unit 2, a bypass unit 3, a flow control valve (valve) 4 and an electric circuit. The sensor unit 2 is composed of a thermal mass flow sensor, and when the gas is wound around the sensor tube 5 and passes through the heated thermo registers 6a and 6b, the thermo registers 6a and 6b are heated by the specific heat of the gas. Is cooled and its resistance value changes.

The resistance value changes of the two thermo registers 6a and 6b are taken out from the bridge circuit 7 as an output,
The amount of change in the resistance value is taken out as an electrical output from the amplifier circuit 8 in correspondence with the gas flow rate. The bypass 3 is a gas flow passage provided in parallel with the sensor unit 2, and detects the total flow rate from the split flow ratio with the sensor flow rate. The comparison control circuit 10 compares the sensor output signal with the setting signal of the setting device 9, and the output of the comparison control circuit 10 controls the valve 4 for flow rate control.
Is controlled so that the target flow rate is achieved. Reference numeral 11 is a flow rate indicator, and 12 is a power source.

In the thermal mass flow rate control device equipped with the mass flow rate sensor, it is obliged to provide a check valve in the gas flow path in order to prevent the back flow of gas, but the back flow of gas is automatically detected. There is no means to do it. As a result, it has been extremely difficult to automatically predict an unexpected situation due to a backflow of gas and a reaction with another gas.

Further, conventionally, a thermistor heated to a temperature higher than the temperature of the fluid and a non-heated thermistor are provided in the gas flow passage to detect the presence or absence of gas flow. Even in such a case, there is no means for automatically detecting the reverse flow of gas.

[0006]

DISCLOSURE OF THE INVENTION The present invention is suitable for a gas backflow detection suitable for application to a thermal mass flow rate control device capable of automatically detecting the occurrence of a backflow of gas and also detecting an overflow. The point is to provide a device.

[0007]

According to the present invention, in a thermal mass flow controller, a mass flow rate signal detecting means for detecting a mass flow rate signal, and a mass flow rate signal and a backflow detection setting signal output by the mass flow rate signal means. And a backflow signal detection / comparison circuit for comparing the levels of the backflow signal and the overflow detection comparison circuit for comparing the levels of the mass flow rate signal output by the mass flow rate detection means and the overflow detection setting signal. It is characterized in that normality and abnormality are displayed based on the backflow and overflow detection signals based on the output signals of the circuit or the overflow detection comparison circuit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a block diagram of a backflow detection device of the present invention. Reference numeral 7 is a flow sensor bridge circuit in which a current is supplied from the constant current circuit 13, and the bridge circuit 7 is constituted by the thermo-resistors 6a and 6b wound around the sensor tube 5 and the resistance elements 6c and 6d. A differential amplifier circuit 8 outputs a thermal mass flow rate signal B. The thermal mass flow rate signal B of the differential amplifier circuit 8 indicates that the output voltage is zero when the gas is not flowing, and the output voltage is increased in proportion to the flow rate when the gas is flowing in the forward direction. When flows in the opposite direction, it decreases in proportion to the flow rate.

The mass flow rate signal B is input to the backflow detection comparison circuit 14 and the overflow comparison circuit 15. The backflow detection setting signal C is used as the other input signal of the backflow detection circuit 14.
Is input, and both signals are compared, and when the backflow detection setting signal C is larger than the mass flow rate signal B, it is output as an error signal D.

Further, an overflow detection setting signal (bypass 100% signal) A is input to the overflow comparison circuit 15 as another input signal, both signals are compared, and the overflow setting signal A is output. When the mass flow rate signal B is large, it is output as an error signal F. The output signals of the two comparison circuits are input to the delay circuit 16, and the delay circuit 16 starts operating when either error signal is present. The delay circuit 16 is composed of a time constant circuit composed of a resistor and a capacitor, which will be described later.

Reference numeral 17 is a waveform shaping circuit for shaping the output of the delay circuit 16 and is composed of a Schmitt trigger circuit having a hysteresis characteristic. A drive circuit 18 is connected to the output side of the waveform shaping circuit 17, and an LED lamp 19 for indicating abnormality and normality and a relay 20 for operating an alarm device are provided.
To drive.

The above is a general description of the backflow and overflow detection device of the present invention. Next, an example of a circuit embodying the block diagram will be described with reference to FIG. Power supply, eg 24
V power source passes through diode D5 and constant current diode D1
And the zener diode D2. The diode D1 sends a constant current to the Zener diode D2 to stabilize the Zener voltage.

Thermo register 6 which constitutes a sensor element
The a and 6b are wound around the sensor tube 5 (FIG. 5) as described above, and the bridge circuit 7 is constituted by the resistors 6c and 6d. By supplying the constant current to the bridge circuit 7, a voltage output proportional to the mass flow rate can be obtained. VR is a resistance for balance adjustment, and adjusts the balance so that the output becomes zero when there is no mass flow rate output.

A1 is a comparison circuit for comparing the voltage detected by the constant current detecting resistor R1 with the reference voltage A (reference voltage source 6.60 V), and stabilizes the current flowing through the bridge circuit 7. A2 and A3 are differential amplifier circuits, which amplify the output of the bridge circuit 7 proportional to the gas flow rate and output the mass flow rate signal B
Is output.

The mass flow rate signal B of these differential amplifier circuits is
When gas is not flowing, VR is adjusted so that the voltage between BA (non-inverting input terminal of the comparator A1) becomes zero. When the gas flows in the forward direction, the voltage of the output B increases in proportion to the flow rate, and when the gas flows in the reverse direction, it decreases in proportion to the flow rate. This is shown in FIG.

The backflow detection comparison circuit A4 compares the backflow detection setting signal C obtained by dividing the reference voltage A by the resistors R2 and R3 with the mass flow rate signal B, and the backflow detection setting signal C is the mass flow rate signal B. When it is larger, the error signal D is output at maximum (full swing).

The excess flow rate detection comparison circuit A5 compares the mass flow rate signal E obtained by dividing the mass flow rate signal B by the resistors R4 and R5 with the reference voltage A, and outputs the flow rate signal E obtained by dividing the flow rate signal B. When it is larger than the reference signal A, the error signal F is output at maximum. Further, when the error signal D is maximum output, the error signal F is forcibly maximum output because the diode D3 is forcibly rendered conductive and the divided flow rate signal E and the error signal D become substantially equal. That is, the maximum output F is obtained when the backflow is detected or the overflow is detected.

The output side of the comparison circuit A5 is provided with a time constant circuit 16 having a resistor R6 and a capacitance C2. When the error signal F fully swings, the output G of the time constant circuit 16 is as shown in FIG. The output waveform is as shown in. A6 is a Schmitt trigger circuit having resistors R7 and R8 and having a hysteresis characteristic at a threshold level H.

The output of the Schmitt trigger circuit A6 is output as a normal or abnormal output. That is, when the error signal F changes from zero to a full swing, the output I of the Schmitt trigger circuit A6 is the time constant circuit 16
Then, the full swing is changed to zero with a delay of, for example, about 2 seconds. When the error signal F changes from full swing to zero, the diode D4 instantly makes a full swing from zero and outputs a normal level.

The output signal I is waveform-shaped as shown in FIG. 4 and is output as a signal indicating an abnormal state and a normal state. When the signal is normal, the output signal I changes to high level, and when abnormal, it changes to low level. Entered into the base. LED lamp 1 that turns on the transistor and emits green light under normal conditions
9a lights up, and the relay 20 turns on. When an error is detected by detecting the error signal, the transistor Tr is turned off, and only the LED lamp 19b that emits red light is turned on to display the abnormal state. It should be noted that C1, C3, and C4 are capacitors for removing high-frequency noise on the line.

[0021]

As described above, according to the present invention, the use of the check valve can facilitate the detection of the gas reverse flow due to the fact that the conventional thermal mass flow rate control device does not have the reverse flow detection and overflow detection device. Coupled with this, it is possible to prevent unexpected situations.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of an embodiment of the present invention.

FIG. 3 is a diagram showing a mass flow rate signal characteristic of the thermal mass flow rate control device.

FIG. 4 is a waveform diagram showing the operation of the present invention.

FIG. 5 is an explanatory diagram of a conventional thermal mass flow rate controller.

[Explanation of symbols]

 7 bridge circuit 14 backflow signal detection / comparison circuit 15 overflow signal detection / comparison circuit 16 delay circuit 17 waveform shaping circuit 19 LED display lamp

Claims (3)

[Claims] 1. In a thermal mass flow controller, a mass flow signal detecting means for detecting a mass flow signal and a backflow signal for comparing the levels of a mass flow signal output by the mass flow signal means and a backflow detection setting signal. With a detection and comparison circuit,
A thermal mass flow controller, wherein the occurrence of backflow is detected based on the output signal of the backflow signal detection / comparison circuit. 2. In a thermal mass flow controller, a mass flow signal detecting means for detecting a mass flow signal and a back flow signal for comparing the levels of the mass flow signal output by the mass flow signal means and a back flow detection setting signal. A detection comparison circuit and an overflow detection comparison circuit for comparing the levels of the mass flow rate signal output by the mass flow rate detection means and the overflow detection setting signal, and the backflow signal detection comparison circuit or the overflow detection comparison circuit A thermal mass flow rate controller characterized by detecting backflow and overflow based on an output signal. 3. The thermal mass flow controller according to claim 1, further comprising a normal display means and an abnormal display means driven by the output of the comparison circuit.