JPH0317233Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a thermal conduction vacuum gauge using a thin film sensor.

Conventional technology and its problems The heat conduction vacuum gauges currently in general use are:
This is a Pirani vacuum gauge that uses thin platinum wire as the heating resistor. Among these Pirani vacuum gauges, the constant temperature type is particularly widely used because it can measure a wide range without changing the measurement range and does not damage the filament due to red heat. However, even with this constant temperature Pirani vacuum gauge, the measurement range is 10 to 10 ^-3.
Torr, which is often sufficient for industrial purposes, but cannot be used when measurement over a wider range is required, in which case a Penning vacuum gauge, etc., which lacks reliability in reading, cannot be used. It was necessary to use it.

To overcome this drawback, a thin film sensor has been developed whose element has a larger effective surface area than the thin platinum wire ^.
It has been confirmed that measurements can be made up to a degree of vacuum. However, thin film sensors have a resistance of several kΩ compared to thin platinum wires (several tens of Ω under heating).
and the resistance value is large. Therefore, conventional circuits require a higher power supply voltage to heat the sensor to operating temperature. In addition, the Wien Bridge oscillation circuit, which is often used in platinum sensors, cannot be used as a drive circuit as is, resulting in a problem that the device becomes larger.

It is an object of the present invention to solve the problems of the prior art and to provide a thin film heat conduction vacuum gauge with a simple structure using a simple Wien Bridge oscillation circuit.

Means for Solving the Problems The object of the present invention is to provide a series circuit consisting of a first resistor and a first capacitor, a parallel circuit consisting of a second resistor and a second capacitor, and a resistance-temperature characteristic. A thin film vacuum sensor that has a thin film and is placed in a vacuum atmosphere to be measured and a third resistor are bridge-connected,
A power operational amplifier is connected to the connection point between the series circuit and the parallel circuit to form a Wien Bridge oscillation circuit, and the electrical resistance value R ₄ of the first resistor and the capacitance C ₂ of the first capacitor The electric resistance value R ₃ of the second resistor and the capacitance C ₁ of the second capacitor are (R ₃ C ₁ +R ₃ C ₂ +R ₄ C ₂ )/R ₃ C ₂ ≧5. The thin film vacuum sensor is characterized in that the thin film vacuum sensor serves as a gain stabilizing element in the Wien Bridge oscillation circuit, and oscillation output measuring means is provided on the output side of the Wien Bridge oscillation circuit. Achieved by a heat conduction vacuum gauge.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a diagram showing the circuit configuration of a thin film thermal conduction vacuum gauge equipped with a Wien Bridge oscillation circuit B. As shown in the figure, the oscillation circuit B is constructed using a general-purpose power operational amplifier 7, and connects one input terminal to the power operational amplifier to the connection points 20, 21 of the bridge circuit.
A resistor 1 and a capacitor 2 are connected in series to one of two sides extending to , and a resistor 3 and a capacitor 4 are connected in parallel to the other, and the oscillation frequency is defined by these. Connection point 20,2
1, a resistor 5 and a thin film sensor 6 are connected in parallel to the circuit consisting of the resistors 1, 3 and capacitors 2, 4, and the mutual connection between the resistor 5 and the sensor 6 is connected to the other input terminal of the power operational amplifier 7. It is connected. Connection point 20 is connected to the output side of power operational amplifier 7, and connection point 21 is grounded. Power operational amplifiers 7 include μA759, μA791 (manufactured by Fairchild), CA3105 (manufactured by RCA),
Appropriate ones such as μA206 (manufactured by Analog System Co., Ltd.) and 1468 (manufactured by Teledyne Film Corporation) can be used, and as the thin film sensor, for example, a TaN thin film sensor with a negative temperature coefficient of resistance can be used. In a general Wien Bridge oscillation circuit, the resistance values R ₃ and R ₄ of the resistors 3 and 1 and the capacitances C ₁ and C 2 of the capacitors 4 and ₂ are R ₃ = R ₄ C ₁ respectively. = _C2 , but in this case, the voltage applied to the sensor 6 is approximately 67% of the oscillation output voltage, making it impossible to obtain an appropriate operating voltage.

In this example, each value is determined so that R ₄ =10R ₃ and C ₁ =10C ₂ . Therefore, 95% of the oscillation output voltage is applied to the sensor 6. Therefore, the driving voltage of the operational amplifier 7 is, for example, ±
Even at 15V, sensor 6 has a maximum effective voltage of approximately
It can apply up to 10V and can supply sufficient power. In this case, the feedback coefficient of the bridge will be lower, but
Since the amplification factor of the operational amplifier is sufficiently high, oscillation is possible. In order to satisfy the oscillation conditions and to realize the supply of sufficient power to the sensor 6, at least the condition (R ₃ C ₁ + R ₃ C ₂ + R ₄ C ₂ )/R ₃ C ₂ ≧5 must be satisfied. There is a need. Note that R ₄ /
This condition is also satisfied even if R ₃ =C ₁ /C ₂ ≧2. In the example given here, R ₄ /R ₃ =C ₁ /C ₂ =10
That is.

Rectifiers 12, 13, capacitors 14, 15, and a resistor 16 are connected to the output terminal of the operational amplifier 7 via a capacitor 10 and a resistor 11 to form a rectifier as shown in the figure, and an ammeter 30 and a variable resistor 31 are also connected. A drive power source 32 is connected to the drive power source 32 via the drive power source 32 . The variable resistor 31 is provided to obtain an ammeter reading range depending on the degree of vacuum.

Therefore, to measure the degree of vacuum, by placing the thin film sensor 6 in the atmosphere to be measured and applying driving power from the power source 32, the thin film sensor 6 can respond to changes in the degree of vacuum like a normal Pirani vacuum gauge. The amount of heat dissipated from sensor 6 changes, and in response, the voltage changes to keep the temperature of sensor 6 constant based on the properties of the Vienna Bridge oscillator circuit, so the degree of vacuum can be determined by reading the ammeter 30. can.

FIG. 2 shows an example of a vacuum gauge in which a logarithmic amplifier 50 is provided between the rectifier 40 and the ammeter 30.
The rectifying section 40 is constituted by a circuit using operational amplifiers 41 and 42 and diodes 43 and 44 for double-wave rectification and smoothing.

The logarithmic amplifier 50, which is a general-purpose IC, logarithmically converts the output voltage so that a wide pressure range can be displayed without changing the sensitivity, and changes on the low pressure side can be displayed largely.

Effects of the invention As is clear from the above explanation, according to the invention, the electrical resistance values and capacitances of the resistors and capacitors in the Vienna Bridge oscillation circuit are determined to have a ratio different from that of general ones as described above. As a result of relatively increasing the voltage applied to the thin film sensor, the thin film sensor can be operated with a low drive voltage, and the number of external parts is reduced by using a general-purpose power operational amplifier. Based on these, We can provide a thin film heat conduction vacuum gauge with a simple structure.

[Brief explanation of the drawing]

The figures show an example of the present invention; Fig. 1 is a diagram showing the electric circuit configuration of an example of a thin film thermal conduction vacuum gauge;
The figure is a diagram showing an electric circuit configuration of another example. 1, 3, 5...Resistor, 2, 4...Capacitor, 7...
Power operational amplifier, 30... Ammeter, B... Vienna Bridge oscillation circuit.

Claims (1)

[Claims for Utility Model Registration] A series circuit consisting of a first resistor and a first capacitor, a parallel circuit consisting of a second resistor and a second capacitor, and a resistor having temperature characteristics in a vacuum atmosphere to be measured. The thin film vacuum sensor placed in electrical resistance value R ₄ , capacitance C ₂ of the first capacitor, and electrical resistance value of the second resistor
R ₃ and the capacitance C ₁ of the second capacitor are determined to be (R ₃ C ₁ +R ₃ C ₂ +R ₄ C ₂ )/R ₃ C ₂ ≧5, and the thin film vacuum sensor 1. A thin film thermal conduction vacuum gauge, comprising a gain stabilizing element in the Wien Bridge oscillation circuit, and comprising oscillation output measuring means on the output side of the Wien Bridge oscillation circuit.