What is Pirani Gauge? Its Diagram and How it Works
Vacuum systems use the Pirani gauge, a reliable thermal conductivity gauge, to monitor pressures. Marcello Pirani came up with the idea in 1906.
By effectively using a resistance thermometer as the heated element, the Pirani gauge eliminates the use of a thermocouple to detect temperature (as in the thermocouple gauge).
In this reading, we will delve into the definition of a Pirani gauge, its various applications, its components, its diagram, its advantages and disadvantages, and its operational mechanism.
Let’s Begin!
What is a Pirani Gauge?
Vacuum systems use a Pirani gauge, a reliable thermal conductivity gauge, to measure low pressures. It works by suspending a hot metal wire in a tube and exposing it to a gas pressure medium. These hot metal wires consist of thin tungsten, nickel, or platinum wires.
It operates by monitoring the change in heat conductivity and using that information to calculate the system’s pressure. This gauge is appropriate for measuring pressures in the range of 0.1 to 100 pascals at very low pressures.
We use the Pirani gauge to measure pressure at low pressures and high vacuum pressures. it uses a plot graph based on the data obtained.
The Pirani gauge attaches a tube containing a metal filament (typically platinum) to the system for vacuum measurement. A ground glass joint or a flanged metal connector, sealed with an o-ring, is commonly used to make the connection.
After calibration, an electrical circuit connects to the filament, allowing for the measurement of pressure.
When an electric current travels through a conducting wire (platinum filament), it heats up. The wire, hanging in the gas, loses heat to the gas as the gas molecules clash with it and remove heat.
As the vacuum pumps drop the gas pressure, the number of molecules present decreases proportionally, the conductivity of the surrounding media decreases, and the wire loses heat more slowly. Measuring heat loss is an indirect way of determining pressure.
Because the electrical resistance of a wire fluctuates with its temperature, resistance testing also indicates the wire’s temperature. We now use the bridge to determine the change in the filament’s resistance. When calibrated, the change in resistance of the Pirani gauge filament becomes a measure of the applied pressure.
Various systems maintain the wire at a constant resistance R by controlling the current I that passes through it. You can set the resistance using a bridge circuit. The wire receives I2R power, while the gas receives the same amount of power.
As a result, the current required to attain this equilibrium is a measure of the vacuum.
The gauge can handle pressures ranging from 0.5 Torr to 103 Torr. The device may require calibration before obtaining correct readings, as the thermal conductivity and heat capacity of the gas can alter the meter’s readout.
We use other instruments like a Penning gauge to measure lower pressures.
Diagram of a Pirani Gauge
Advantages and Disadvantages of a Pirani Gauge
Advantages:
Below are the benefits of a Pirani gauge in its various applications.
They’re tough and affordable.
At low pressure, it produces reliable results.
You can read pressure from a distance.
We do not recommend the thermocouple gauge, another type of thermal conductivity gauge.
It is preferable because it is 10 times faster and can monitor a larger range of pressures.
Disadvantages:
Regular examination of the Pirani gauge is necessary.
To calibrate the Pirani gauge, use different gases.
Its operation necessitates the use of electricity.
Vacuum systems use a Pirani gauge, a reliable thermal conductivity gauge, to measure low pressures. It works by suspending a hot metal wire in a tube and exposing it to a gas pressure medium.
These hot metal wires consist of thin tungsten, nickel, or platinum wires. This article covers the definition, applications, parts, diagram, working, advantages, and disadvantages of the Pirani gauge.
