A temperature switch trips an electrical contact the instant temperature crosses a set threshold, turning a hot or cold limit into a direct on-off action. Like the household thermostat it is related to, it does not report the temperature - it decides whether the limit has been passed and acts. This guide explains how a temperature switch works, what set point and deadband mean, and why the TSH and TSL family is the backbone of compressor and bearing overtemperature shutdown.
Temperature Switch in one line: A temperature switch is a discrete device that opens or closes an electrical contact when temperature rises above or falls below a preset value, providing a trip or alarm signal rather than a continuous reading. High-temperature switches (TSH) and low-temperature switches (TSL) are used to shut down equipment and interlock processes, and they differ from a temperature transmitter, which outputs a continuous signal for trending and control.
A temperature switch senses temperature with an element that changes state at a threshold and drives a contact. Many use a bimetallic disc or strip that snaps at a target temperature, the same principle as a simple thermostat. Others use a filled bulb-and-capillary system, where a fluid sealed in a bulb expands with heat and pushes a bellows that trips the switch, letting the sensing bulb sit at the process while the switch body sits elsewhere. Electronic temperature switches use an RTD or thermistor and threshold logic. Whatever the sensing method, an adjustable set point defines the temperature at which the contact changes state.
As with any trip device, deadband is essential. Deadband is the gap between the temperature at which the switch trips and the temperature at which it resets, and it stops the contact from chattering when temperature hovers at the set point. Without deadband, a temperature drifting right at the limit would rattle the switch on and off and cause nuisance trips; with it, a high switch stays tripped until temperature falls back well below the set point. A high-temperature switch trips as temperature rises through its set point, and a low-temperature switch as temperature falls through its set point, so the two together define a safe temperature window.
In field tags, a temperature switch high is a TSH and a temperature switch low is a TSL, and these are the workhorses of rotating-equipment protection. Compressors and engines are especially dependent on them: a TSH on discharge gas, cooling water, or lube oil trips the machine when temperature climbs too high, catching a fouled cooler, a lost coolant flow, or a lube problem before heat destroys the equipment. Because overtemperature builds toward serious damage, the direct, hardwired action of a switch is valued for its speed and certainty.
Bearings are a classic application. A rising bearing temperature is one of the earliest and clearest signs of impending mechanical failure - loss of lubrication, misalignment, or overload - and a bearing temperature switch trips the machine before the bearing seizes. Low-temperature switches guard the other extreme: a TSL can prevent equipment from starting or running when a fluid is too cold to handle safely, such as blocking a start until lube oil warms to a workable temperature. In every case the switch reduces a temperature limit to a simple protective action wired straight into the shutdown circuit, completing the process-switch set alongside pressure, level, and flow switches.
A temperature switch and a temperature transmitter cover the same variable in different ways and often work together. The transmitter feeds a cloud SCADA such as Merobix the continuous temperature - the trend that lets operators watch a bearing or discharge temperature creep upward over hours and intervene early. The switch provides the independent hard limit: a discrete trip that fires whether or not anyone is watching the trend and without relying on the monitoring software to interpret a value.
That separation is deliberate protection design. The analog transmitter gives early warning and the room to act before anything trips, while a dedicated TSH stands as the final, hardwired shutdown that does not share a failure mode with the measurement. Keeping the safety trip on its own switch rather than deriving it from the transmitter avoids putting protection and measurement in the same basket, which is the core idea behind layered safeguards.
For remote sites, wiring the switch's state into the RTU turns each trip into a reported event. The control room is annunciated the instant a compressor or bearing switch trips, so the discrete shutdown is logged next to the continuous temperature record and operators can see exactly what happened and why. The transmitter gives the picture and the lead time to prevent a trip; the switch gives the guaranteed last-line action - and on an unmanned site both reach the control room through the same monitoring platform.
A temperature switch flips an electrical contact when temperature crosses a set point, giving a discrete trip or alarm signal. A temperature transmitter outputs a continuous analog signal proportional to temperature for trending and control. Switches drive direct, hardwired shutdowns; transmitters let operators read and trend the actual temperature and alarm on it before a limit is reached.
TSH is a temperature switch high, which trips when temperature rises above its set point, and TSL is a temperature switch low, which trips when temperature falls below its set point. Together they define a safe temperature window. They are widely used to shut down compressors, engines, and bearings on overtemperature, and to block operation when a fluid is too cold to run safely.
A rising bearing temperature is an early sign of trouble such as lost lubrication, misalignment, or overload. A bearing temperature switch trips the machine when temperature climbs past its set point, stopping it before the bearing seizes and causes major damage. Because the switch acts directly on a contact, the trip can be wired straight into the shutdown circuit for a fast, certain response.
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