JPH01196609A - Control circuit for mass-flow controller - Google Patents

Abstract

PURPOSE:To obtain the high speed responsiveness of flow quantity control and to cause a mass-flow controller to be compact without increasing a circuit constituting element by causing the compensating frequency of a phase compensating circuit to be almost the same as the attenuating frequency of a sensor circuit. CONSTITUTION:A compensating frequency (fo) of a phase compensating circuit 3 is caused to be almost the same as an attenuating frequency (fs) of sensor circuits 2a and 2b. Accordingly, even when the flow quantity change in a conducting tube 1 is small and a detecting voltage in the sensor circuits 2a and 2b is the attenuating frequency (fs), a gain can increase by the phase compensating circuit 3. Then, even when the flow quantity change is small, a flow quantity control valve 6 can be controlled to be prescribed flow quantity. Thus, without increasing the circuit constituting element, the responsiveness can be made high speed and the mass-flow controller can be made compact.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a control circuit for a mass flow controller that controls the flow rate of a reaction gas, etc. supplied to a CVD apparatus or a vapor deposition apparatus.

``Prior art'' A conventional FFI mass flow controller winds a temperature-sensitive coil whose resistance value changes depending on temperature changes at two locations on a gas supply conduit, and detects the flow rate based on the temperature difference between the two locations due to the flow of gas. The control valve installed in the conduit was controlled according to the detected value.

To achieve high-speed response control of the mass flow controller, there are two methods:
Alternatively, a method is known in which the output gain of the sensor circuit is increased using a phase compensation circuit. Furthermore, in order to control the mass flow controller at high speed and to prevent it from being affected by the ambient temperature, there is also known a device in which a constant temperature circuit is incorporated into the temperature sensing coil (Japanese Patent Application Laid-Open No. 81-128123).

"Problem to be Solved by the Invention" Even if the thermal time setting of the sensor circuit of the mass flow controller is reduced or the output gain of the sensor circuit is increased with a phase compensation circuit, the response time is still 4 to 6 seconds. There were problems such as insufficient control of flow rate and uncertain flow control.

In addition, the type that incorporates a constant temperature circuit into the temperature sensing coil,
As the number of circuit components increases, the circuit becomes complicated and becomes larger, which is a problem.

An object of the present invention is to provide a smaller mass flow controller that increases the responsiveness of flow rate control without increasing the number of circuit components of a conventional mass flow controller.

"Means for Solving the Problems" A control circuit for a mass flow controller of the present invention will be explained with reference to a model diagram shown in FIG.

The sensor circuit includes a flow rate sensor 2a provided in the conduit 1 and a sensor amplification circuit 2b that amplifies the sensor voltage, so that a detected value corresponding to the flow rate flowing through the conduit 1 can be obtained. The detected value is increased in gain in a high frequency range by a phase compensation circuit 3, and further compared with a reference voltage 5 by a comparison amplifier circuit 4. Then, by the output of the comparison amplifier circuit 4, the conduit 1
A control valve 6 provided at the front is controlled.

The compensation frequency f- of the phase compensation circuit 3 is made almost the same as the attenuation frequency fs of the sensor circuit, as shown in FIG. 2, so that the time constant of the sensor circuit and the time constant of the phase compensation circuit are almost the same. I did it like that.

"Operation" In the mass flow controller control circuit of the above means, the compensation frequency of the phase compensation circuit is made almost the same as the attenuation frequency of the sensor circuit. Even if the attenuated frequency is
The gain is increased by the phase compensation circuit. Therefore, even when the change in flow rate is small, the flow control valve can be controlled to a predetermined flow rate, improving responsiveness.

"Example" An embodiment of the present invention will be explained with reference to FIG.

Two windings Rsl and Rs are installed around the outer circumference of the conduit that supplies gas etc.
2 are provided a little apart in the direction of fluid flow. Each winding is of a type whose resistance value changes depending on temperature changes. The temperature is raised by passing current from the power supply through the windings Rsl and Rs2, and when the temperature rises, the circuit Ic
Return the current to 5.

The current is controlled to be constant. Also, the winding Rs1, R
s2 forms a bridge circuit together with resistors R1 and R2, and is set so that when the gas flow rate is O, the bridge voltage is also O by changing the resistance value of resistor R1.

When gas etc. flows through the conduit, the heated winding 11R
The gas receives and takes different amounts of heat from sl and FLs2, creating a temperature difference between both windings. Therefore, the winding Rsl
, the resistance value of Rs2 changes, the equilibrium state of the bridge circuit is disrupted, and a bridge voltage is generated. The bridge voltage is amplified by the circuit Icl, and the resistor VRI is adjusted so that DC5V is obtained when the maximum flow rate specified by the mass flow controller is supplied. Further, the capacitor C1 provided in parallel with the circuit Icl is for cutting noise in the sensor voltage. In addition, the senna circuit 2 consists of a circuit that detects the above sensor voltage and a circuit that amplifies it.
will be constructed.

In order to input the output of the sensor circuit 2 to the phase compensation circuit 3, the output end of the circuit Icl is connected to the resistor R8. The phase compensation circuit 3 includes a resistor R1 for determining the sensor output amplification degree.
3, R7, R8, and a resistor R9 for low frequency output amplification.
The compensation frequency of the one-phase compensation circuit 3, which is composed of R[0, capacitors C2 and C3, is determined by the capacitor C2 and the resistor R9.

If the attenuation frequency of sensor circuit 2 is f$, its reciprocal (
(time constant) was set to have the following relationship: 1/fs=C2·R9. In this embodiment, since the time constant of the sensor circuit 2 is, for example, 3.6 seconds, the time constant of the phase compensation circuit 3 is 1/
For example, from the following equation, R9・C2=3 X106 (Ω) Xl, 2 XIO
逼(F)=3.6 C2 is 1.2 x 10' (F), R9 is 3 x
106 (Ω). By setting R8 and 02 in this way, the compensation frequency of the phase compensation circuit 3 becomes the same as the attenuation frequency of the sensor circuit 2, and a sensor voltage that compensates for the high frequency range of the frequency characteristics of the sensor circuit 2 can be obtained. .

Note that it is also applicable to a range where the compensation frequency of the phase compensation circuit 3 and the attenuation frequency of the sensor circuit 2 are almost the same.

In order to input the output of the phase compensation circuit 3 to the comparison amplifier circuit 4, the output terminal of the circuit Ic2 is connected to the resistor R11. The comparison amplifier circuit 4 has R12/R11 in the circuit Ic3.
Resistors R11, R12 and capacitor C4 that amplify the voltage, variable capacitor Vt that provides the reference voltage to be compared, and resistor R
14, and outputs in response to the sensor voltage, that is, in response to the difference voltage between the flow rate and the reference voltage. Resistance again! j15 and circuit Ic4 are buffer circuits that output the flow rate signal voltage to the outside.

The output end of the comparison amplification circuit 4 is connected to the valve drive circuit 7,
The valve drive circuit 7 controls a control valve 6 provided in the conduit. Based on the detected value corresponding to the flow rate in the sensor circuit 2, the valve drive circuit 7 is controlled via the phase compensation circuit 3 and the comparison amplification circuit 4, and the flow rate in the conduit is controlled in a predetermined manner.

"Effects of the Invention" The present invention makes the compensation frequency of the phase compensation circuit almost the same as the attenuation frequency of the sensor circuit, so the response speed of control valve control is several times lower than that of a conventional control circuit. 1, which further improves responsiveness.

Furthermore, since it is not necessary to increase the number of circuit components to obtain high-speed response, the mass flow controller can be made compact.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an outline of a control circuit for a mass flow controller of the present invention, FIG. 2 is a graph showing frequency characteristics of a sensor circuit and a phase compensation circuit, and FIG. 3 is a control circuit diagram of a mass flow controller. 2; Sensor circuit 3; Phase compensation circuit 4; Comparison amplifier circuit 6; Control valve applicant Hitachi Metals Co., Ltd. Agent Patent attorney Katsu Maki Frequency [Hzl Fig. 3 +VCc

Claims (1)

[Claims] A mass flow controller control that uses a sensor circuit to detect temperature changes corresponding to the flow rate in a conduit, increases its output gain with a phase compensation circuit, and then controls the flow rate control valve installed in the conduit via a comparison amplifier circuit. In the circuit,
A control circuit for a mass flow controller, characterized in that the compensation frequency of the phase compensation circuit is made almost the same as the attenuation frequency of the sensor circuit.