Working Principle of Thermocouple Vacuum Gauge
The operating principle of thermocouple Vacuum Gauge is that the conducting ability of gas in vacuum or low pressure depends on the pressure i.e., it is a function of pressure. The measurement of vacuum using thermocouple gauge is shown in figure 1.
Figure 1: Thermocouple Vacuum Gauge.
Construction and Working of Thermocouple Vacuum Gauge
The thermocouple and heater element are placed inside the chamber whose vacuum is to be measured. When the supply voltage is applied to the circuit using a battery. some current will flow in the circuit which heats the heater element.
Since the thermocouple is attached (welded) to it. the developed heat will be sensed by the thermocouple. Here, the presence of vacuum causes the heat element to loose some heat. In other words. variations in the vacuum causes the temperature to change.
This change in temperature is measured by thermocouple and it develops a proportionate amount of voltage which is indicated by the voltmeter. Here, the reading of voltmeter is calibrated directly in terms of applied pressure or vacuum.
Advantages of Thermocouple Vacuum Gauge
- Rugged construction.
- Cost is less.
- Simple operation.
- We can note the readings directly since the output of thermocouple is directly calibrated in terms of pressure.
Disadvantages of Thermocouple Vacuum Gauge
- Short life of filament
- It requires electrical supply voltage to operate.
Minimization of Radiation Effects in Thermocouple Vacuum Gauge
The heat loss occurs in both the types of thermal conductivity gauges (i.e.. thermocouple The operating principle of thermocouple Vacuum Gauge is that the conducting ability of gas in vacuum or low pressure depends on the pressure (i.e., it is a function of pressure and pirani gauge) because of conduction and radiation. This is due to the hot and cold surface temperatures. The radiation losses can be minimized with the help of surface having low emissivity. If the diameter of the wire used in the device is reduced. then the radiation effect can be controlled.
When the current passes through the resistor there results power loss iii the instrument because of rise in the temperature value. Based upon the gas medium of the thermal conductivity, the device achieve constant temperature. The transfer of heat takes place through conduction and radiation via gas to the atmosphere. The radiation loss can be reduced by keeping the enclosure tube cool.
Applications of Thermocouple Vacuum Gauge
- Can be applied in the measurement of low vacuum.
- Can be applied in the measurement of pressures of ultra high vacuum.