KR20040013341A - Circuit of the Peltier vacuum gauge based on time-sharing method - Google Patents

Abstract

PURPOSE: A time sharing type Peltier vacuum gauge driving circuit is provided to precisely measure a vacuum degree by using thermocouples and to perform heat source and temperature sensor functions through a time sharing method. CONSTITUTION: A time sharing type Peltier vacuum gauge driving circuit includes a square wave signal generating device, which generates square wave signals with maintaining a short dead time(7). A switch(3) is provided to connect the square wave signals to thermocouples(1) installed in a vacuum vessel(2) in order to heat or cool the thermocouples(1). The switch(3) is connected to a voltage meter in such a manner that the voltage meter measures the temperature of the thermocouples(1) during the dead time(7). The thermocouples(1) are heated or cooled based on the square wave signals.

Description

Circuit of the Peltier vacuum gauge based on time-sharing method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for vacuum gauges, and more particularly to a Peltier vacuum gauge drive circuit. There are various types of vacuum gauges depending on the measuring range and operating method of the vacuum region. The Peltier vacuum gauge is a low vacuum gauge in terms of the vacuum measuring range, and belongs to a thermal conduction gauge. Low vacuum gauges typically measure a vacuum of about 10 ^-4 Torr at atmospheric pressure (760 Torr). Meanwhile, the thermally conductive vacuum gauge includes a Pirani vacuum gauge, a thermocouple vacuum gauge, and the like, and the thermal conductivity of gas molecules varies according to the vacuum degree.

1 and 2 are conventional thermally conductive vacuum gauge driving circuits. First, the piranha gauge drive circuit ([FIG. 1]) has a filament (resistance R _s ) in the vacuum container 1 forming one arm of the Wheatstone bridge. The change in temperature of the filament with the degree of vacuum results in a change in resistance and breaks the balance of the bridge, which is fed back through the differential amplifier 2 to correct the voltage 3 across the bridge. That is, it is a method of indirectly knowing the degree of vacuum by measuring the voltage of the bridge according to the pressure which makes the temperature (resistance) of the filament constant. It is a direct current (DC) driving method and the signal magnitude is about several volts.

As shown in the figure, the driving circuit of the thermocouple gauge ([Fig. 2]) forms a cross junction, one side is a filament and the other side is a thermocouple, and the filament and the temperature sensor are separately configured to control the temperature of the filament. Direct reading with the voltmeter (6) is used. It is also a direct current (DC) driving method and the filament is driven by a constant current (5). The signal magnitude is on the order of tens of millivolts (mVolt).

As described above, the driving circuit for measuring the vacuum degree with a thermal conductivity gauge is composed of a portion for flowing a current to heat the filament and a portion for measuring the temperature change of the filament according to the vacuum degree, and the Piranha vacuum gauge is a Wheatstone bridge. The filament is used simultaneously as a temperature sensor, and the thermocouple gauge is characterized by a heat source and a temperature sensor configured separately.

1) The first object is to provide a driving circuit for the Peltier vacuum gauge, which is a vacuum gauge for low vacuum.

2) Compared to the conventional thermally conductive vacuum gauge drive circuit (a circuit consisting of a heat source and a temperature sensor or a circuit measuring the degree of vacuum using a filament as one arm of the Wheatstone bridge), the thermocouple alone Can be used to measure the degree of vacuum more accurately,

3) Furthermore, it aims to provide a circuit that more accurately measures the degree of vacuum in the vacuum area of 10-760 Torr, which could not be accurately measured by conventional thermocouple gauges and pyranage gauges.

1 is a driving circuit of a conventional piranha gauge

2 is a driving circuit of a conventional thermocouple gauge

3 is a representative diagram of a time division type Peltier vacuum gauge driving circuit.

FIG. 4 is a Peltier vacuum gauge driving circuit that improves a problem caused by noise and pressure change over time by measuring a differential signal using two thermocouples by applying a time division driving circuit.

* Code description for main parts of drawing

[Figure 1]

1, 4: vacuum chamber

2: Differential Amplifier for Detecting and Feedbacking Unbalanced Signals at Wheatstone Bridge

3: voltage across Wheatstone Bridge

R, R ₁ , R ₂ : Resistors constituting Wheatstone Bridge

[Figure 2]

4: vacuum vessel

5: voltage source for heating the filament

6: voltmeter measuring the temperature of the thermocouple

[Figure 3]

1: Thermocouple used as a heat source and temperature sensor

2: vacuum container

3: Switching when driving currents for heating / cooling thermocouples

4: Switching when measuring thermocouple temperature

5: forward current drive (heating of thermocouple junction)

6: Reverse Current Drive (Cooling of Thermocouple Junction)

7: Dead time for measuring thermocouple temperature

8: Temperature change when driving current in thermocouple

T _H , T _L , ΔT: Time and temperature difference of thermocouple

[Figure 4]

1: Thermocouple used as a heat source and temperature sensor

2: vacuum container

3: Switching when driving currents for heating / cooling thermocouples

4: Switching when measuring thermocouple temperature

5: Differential Amplifier Amplifies Temperature Difference Between Two Thermocouples

6: Phase shift to shift the phase of the input signal 180˚

7: Square wave current drive with short dead time

The present invention relates to a drive circuit of a Peltier vacuum gauge consisting of one thermocouple, characterized in that the function of the heat source and the temperature sensor is enabled through a time division method. The time division type Peltier vacuum gauge driving circuit according to the present invention,

A square wave signal generator comprising a short dead time;

A switch that connects said generation signal to a thermocouple to heat / cool the thermocouple or to a voltmeter to measure the temperature of the thermocouple during standby time;

A thermocouple heated / cooled by the generated signal;

A voltmeter to measure temperature during standby time;

And the like.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. First, the Peltier effect will be described. When current flows through a thermocouple consisting of different conductors A and B at a certain temperature T, the differential amount of time of heat (Q) at the junction of the thermocouples is represented by Equation 1 due to the difference in electrochemical potential of the two conductors. Difference occurs.

Here, Δ S is a coach, I open the power line is two conductive current. Therefore, depending on the direction of the current, the junction of the thermocouple can be heated or cooled, which is called the Peltier effect.

When the current is applied (5, 6) with the thermocouple 1 in the vacuum vessel 2 as shown in FIG. 3, the junction of the thermocouple repeats heating / cooling according to the direction of the current. When the current direction is forward 5 or reverse 6 the switching 3 is connected to a current drive contact. During this period, the junction of the thermocouples acts as a heat source. During a short dead time (7), the current drive is turned off, switched to a voltmeter (4) to see the voltage associated with the thermocouple's temperature. Reading the temperature T _H , T _L between two successive waiting times gives us the amplitude of the temperature oscillation (ΔT) and indirectly obtains the degree of vacuum from the temperature amplitude. Here, it is assumed that the waiting time is shorter than the period of the square wave so that the current driving of the thermocouple is close to the ideal square wave driving. Qualitatively, if the degree of vacuum is good, the temperature amplitude is large because there is little heat loss due to gas molecules, and it is small near atmospheric pressure. On the other hand, the reason for performing AC square wave driving is to have a good sensitivity even in the vicinity of the atmospheric pressure by including the specific heat measurement of the gas molecules in the vicinity of the atmospheric pressure.

In a time division manner, the thermocouple junction acts as a heat source to be heated / cooled during the current drive (3) of the thermocouple, and as a temperature sensor during the connection (4) to the voltmeter during standby time, so that one thermocouple is used as a vacuum sensor. Peltier vacuum gauge can be used as a simple circuit. On the other hand, the disadvantage of the time division type vacuum gauge driving circuit is that 1) the temperature is measured at different times so that it is not possible to cancel the random noise, and 2) the drift error when the pressure changes rapidly with time. (drift error) (Because the thermocouple is also a resistor, due to Joule heating by current driving, the temperature of the entire thermocouple changes when the pressure changes.)

4 is a method of applying a square wave of 180 ° out of phase to two thermocouples and measuring the voltage difference with a differential amplifier in order to solve the problems caused by measuring temperature at different times. In the vacuum vessel 2, two thermocouples 1 are driven by a square wave 7 having a waiting time 3, and one thermocouple has a 180 ° different phase through a phase shifter 6. Thus, during one cycle of current driving, one thermocouple is heated / cooled and the other thermocouple is cooled / heated. When the temperature difference between the two thermocouples is measured by the differential amplifier 5 during the standby time 4 of the square wave, the temperature difference ΔT can be known at the same time, unlike in FIG. 3. Therefore, the in-phase noise can be canceled, and furthermore, since the temperature change of the two thermocouples by Joule heating is the same (Joule heating regardless of the current direction), the drift error due to the pressure change can be eliminated.

1) Since a single thermocouple can be used as a heat source / temperature sensor through time division, a Peltier vacuum gauge driving circuit can be manufactured with a simple circuit configuration.

2) By using two thermocouples and driving 180 ° of different current in phase to measure the temperature difference between the two thermocouples at the same time, the phase noise is canceled and the Peltier vacuum gauge driving circuit without signal distortion due to pressure change can be manufactured. Can be.

Claims (2)

In the Peltier vacuum gauge drive circuit, A square wave signal generating device having a short dead time; A switch that connects the generated signal to a thermocouple for heating / cooling the thermocouple or a voltmeter to measure the temperature of the thermocouple during standby time; A thermocouple heated / cooled by the generated signal; A time division Peltier vacuum gauge drive circuit comprising a voltmeter for measuring temperature during standby time In the Peltier vacuum gauge drive circuit, A square wave signal generating device having a short dead time; A phase shifter for shifting a phase of the generated signal by 180 °; A switch that connects the generated signal to a thermocouple to heat / cool the thermocouple or to a differential amplifier to measure the temperature difference between the two thermocouples during standby time; Two thermocouples heated / cooled by the generated signal; Time division Peltier vacuum gauge drive circuit comprising a differential amplifier for measuring the temperature difference between two thermocouples during standby time