A danfoss pressure switch is a device that operates an electrical contact when a preset fluid pressure is reached. The switch makes an electrical contact on either pressure rise or pressure fall from a certain preset pressure level. Pressure switches are in a wide range. A danfoss pressure switch should not be confused with a pressure transducer. A pressure transducer converts pressure into an electrical output signal. Read our pressure transducer technical article to learn more about them. Mechanical pressure switch A mechanical pressure switch uses a spring and a diaphragm, or piston, to control at what pressure the micro-switch is triggered. The spring is the opposing force to the inlet pressure and the springs pretension is adjusted with a set screw or knob. The spring pretension directly correlates to the pressure at which the switch makes an electric contact. When the pressure drops, the switch resets to its original state. The difference between the switch point and reset point is called hysteresis. Often this is expressed as a percentage of the switch point value, for example, 20%. The manufacturer defines the hysteresis, and for most mechanical switches, it is not configurable by the user. These pressure switches usually have three different types of contact: normally open (NO), normally closed (NC), and changeover (SPDT) contacts. Changeover contacts are for both NO and NC operation. The mechanical pressure switch is better suited for handling high voltages and amperages than an electronic pressure switch. They can be used to make a contact change for an increase or decrease in pressure.