Gas-Actuated Temperature Switch

Above the range of vapour-pressure systems, the gas-actuated temperature switch takes over. Its bulb, capillary and measuring element are filled with an inert gas whose pressure rises linearly with absolute temperature, giving a wider range, a linear scale and better repeatability. The measuring element moves a snap-action microswitch at the adjustable set point, with no electrical power required for sensing.

The range is −30 to +600 °C, which covers thermal oil systems, exhaust gases, furnace zones, glass and metal processes, with repeatability better than 0.5 % of span. Contacts are SPDT or DPDT rated up to 20 A at 250 VAC. The 316 stainless steel bulb mounts through a ½" or ¾" thread or a thermowell, directly or on a capillary up to 10 m, and the enclosure is aluminium or 316L in weatherproof or explosion-proof versions. Pressure capability is determined by the thermowell and process connection.

Accessories are capillary, compression fittings, mounting brackets, and helical or surface bulbs.

Applications are high-temperature safety monitoring, alarms and shutdowns, and hazardous-area installations in chemical, petrochemical, oil and gas, power, mining and glass industries. For ranges up to 250 °C in general process duty, the compact temperature switch is the standard choice.