The pressure or temperature to be controlled is applied to a sensor (manometric, tube, bellows, bulb). Whenever there is a change of pressure or temperature, the sensor is distorted and acts on a force balance connected to a microswitch. Opposite this sensitive element, an adjustable spring enables the working point to be adjusted : whenever the pressure on the sensor is sufficient to counter the spring pressure, the force balance changes position. Adding a second adjustable spring permits greater or lesser increase of the hysteresis (dead-band) or to act on dislocation between the two contacts if the instruments is thus equipped. Search industrial control device within a few mouse clicks
