The A20 Series (2 inch/51 mm dial) and the A25 Series (2-1/2 inch/64 mm dial) Swichgage® models are diaphragm-actuated, temperature-indicating gauges, with built-in electrical switches for tripping alarms and/or shutdown devices.
All models of these rugged, built-to-last instruments are fully sealed from the environment by the unique combination of a polycarbonate case and lens, a polished stainless steel bezel and O-ring seals.
These vapour/pressure actuated gauges feature a sealed capillary tube and a sensing bulb. When subjected to heat, the liquid in the sensing bulb changes to vapour creating pressure against a diaphragm mechanism. The diaphragm translates this vapour pressure into a mechanical gauge reading.
For series A20T and A25T, the gauge pointer acts as a temperature indicator and as one pole switch which completes a circuit when it touches the adjustable limit contact. Contact(s) are isolated from ground. They have a self-cleaning motion to enhance electrical continuity.