Thermal conductivity measurement is commonly used to control electron combustion in CO2 recorders. It is used to determine the amount of hydrogen in nitrogen air and oxygen, by this it can determine ammonia, sulfur, dioxide, hydrocarbon mono oxide, and hydrogen sulfide and oxygen, it is of two types.
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(i) Pirani Gauge
This gauge is used to measure pressure ranging from 10¯¹⁰ to 0 mmHg.
Construction
It mainly consists of two cells, these cells are made of hard glass, and they have a filament of tungsten, in which a cell is sealed on the vacuum. This cell is called a temperature compensation cell. The second cell is connected to the gas whose pressure is to be measured, this cell is also called the measuring cell.
The current passing through the filament is kept constant with the help of a wheel stone bridge and it is connected to an E.M.F indicating instrument.
Working Principle of Pirani Gauge
Its working principle is that the heat loss due to conduction and convection in a hot resistance wire is proportional to the pressure of the gases filled on all four sides of that resistance wire. In this, an equal electric current is passed through the filaments of both cells so that they get heated.
After this, the pressure of the gas is to be determined. It is connected to the measuring cell due to which heat loss occurs due to conduction and convection. Due to this, the temperature of the measuring filament falls, but due to keeping the compensation cell in a vacuum, its temperature does not fall, thus due to the temperature difference between the two filaments, E.M.F is generated, which is read by the potentiometer. This e.m.f is related to the pressure of the gas to be measured being proportional.
Advantages
1. The Pirani Gauge is a highly accurate and reliable vacuum gauge used to measure pressure in the range of 10-3 to 10-7 Torr.
2. It is an essential tool for many applications such as semiconductor fabrication, vacuum deposition, sputtering, and electron microscopy.
3. The Pirani Gauge offers numerous advantages over other types of vacuum gauges including its low cost, fast response time, high accuracy, and repeatability.
4. Furthermore, it can be easily calibrated with only minimal maintenance required.
5. It is also a very robust instrument that can be used in harsh environments and can withstand high temperatures.
(ii) Thermo Couple Gauge
It is apparent that the basic principles of operation it is the same as in the Pirani gauge where the temperature of the heated filament depends on the heat loss by conduction and convection through the gas surrounding the filament in the thermocouple gauge however the temperature of the filament is measured by a fine wire thermocouple directly attached to a filament.
Thermo Couple Gauge Advantages
1. It is a reliable and accurate temperature-measuring instrument designed for use in industrial and commercial environments.
2. The device uses two thermocouples connected in series to measure the temperature change.
3. This allows for highly accurate readings even in extreme temperatures.
5. The thermocouple gauge also provides long-term stability, making it suitable for long-term monitoring applications.
6. It is easy to set up and operate, making it ideal for both experienced and novice users.
Thermocouple Gauge Uses
Thermocouple gauges have various uses in industry and research, including monitoring temperature in industrial processes, measuring temperature in engine cylinders, controlling the temperature in ovens and furnaces, as well as studying heat transfer rates.
It is also widely used in medical equipment such as incubators and blood analyzers.