Pirani Sensor
By DarthVader
Date: 2026-11-14
Topic: 262 see comments
Post views: 2
Pirani Sensor
- The Pirani sensor is a MEMS (micro-electro-mechanical-system) device.
- Measures gas pressure ranging from 1 Pa to 105 Pa (105 Pa = atmospheric pressure at sea level)
- The sensor consists of a heated wire which conducts heat into the surrounding air at different rates depending on surrounding gas pressure.
- Silicon nitride (Si3Ni4) is used to support the conductive Platinum (Pt) wire, because silicon nitride is a strong insulator and so heat can only leave the wire through the surrounding gas and not its supporting structure. (Thermal conductivity of Si3Ni4 = 3 W m-1 K-1) It also insulates the supporting structure from the electric current passing through the wire which is used for resistive heating, and measuring the temperature change in the wire. (The relationship between resistance and temperature in the wire is almost linear).
- Platinum is used for the wire because it is not oxidised when heated, so the material properties such as electrical resistivity remain constant through the wire.
- The Pirani sensor usually makes up one resistor in a Wheatstone bridge.
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