Vacuum switches are a type of pressure switch that functions in the vacuum end of the pressure spectra. They measure vacuum pressure (negative pressure). Their primary purpose is to monitor vacuum status and open or close a connection when there is a change in the vacuum level of a liquid or gas. Vacuum switches are available that produce signals for electromechanical, solid-state or pneumatic switches upon reaching a specific vacuum level. The most important parameter to consider is the vacuum range that is needed for the switch to actuate, or the range over which linear output is needed.
Vacuum switches can have an electro-mechanical or solid-state switch construction. The normal state can be normally open (NO), or normally closed (NC). They can have single poles (SP), double poles (DP), or more than two poles. The throw type on a vacuum switch can be single throw (ST) or double throw (DT). The switch may be TTL compatible. Electrical characteristics of vacuum switches to consider include switched current, switched AC volts, and switched DC volts.
Vacuum switches may be a sensor element or chip, a sensor or transducer, an instrument or meter, a gauge or indicator, a recorder or totalizer, and a controller. A sensor element or chip denotes a "raw" device such as a strain gage, or one with no integral signal conditioning or packaging. A sensor or transducer is a more complex device with packaging and/or signal conditioning that is powered and provides an output such a dc voltage, a 4-20mA current loop, etc. An instrument or meter is a self-contained unit that provides an output such as a display locally at or near the device. Typically also includes signal processing and/or conditioning. A gauge or indicator is a device that has a (usually analog) display and no electronic output such as a tension gage. A recorder or totalizer is an instrument that records, totalizes, or tracks force measurement over time. Includes simple datalogging capability or advanced features such as mathematical functions, graphing, etc.
Sensor technologies for vacuum switches include piston, diaphragm, strain gauge, semiconductor piezoresistive, piezoelectric, MEMs, variable capacitance, and vibrating element. Other important parameters to consider include switch accuracy, the type of material to be measured, features such as temperature compensation and temperature output, and electrical output. Important operating parameters to consider include operating temperature, maximum shock, and maximum vibration.