Pressure Switches Glossary

A

Absolute Pressure

The difference between zero pressure (a perfect vacuum) and some known pressure.

Accuracy (Repeatability)

The maximum allowable set-point deviation of a single pressure switch under one given set of environmental and operational conditions.

Actuation Point (Set Point)

The point at which the switch is actuated to either open or close the electrical circuit, depending on how the switch is wired.

Ambient Pressure

Adjacent (not necessarily atmospheric) pressure immediately surrounding the switch.

Ambient Temperature

Adjacent (not necessarily atmospheric) temperature immediately surrounding the switch.

Atmospheric Pressure

The actual weight of the earth’s atmosphere at a given locale and altitude. Atmospheric pressure at sea level is approximately 14.7 psia or 30 inches of mercury.

D

Deadband (Differential / Hysteresis)

The difference between the actuation point and the deactuation point.

Deactuation Point

Once the switch is actuated (See Actuation Point), the point at which the switch then changes state (open or closed depending on wiring) to return it to its initial state.

Differential

See Deadband.

Double-Pole Double-Throw (DPDT)

Switches which make and break two separate circuits. This circuit provides a normally open and normally closed contact for each pole.

Differential Pressure

The differential between two independent pressures.

E

Electrical Switching Element

Opens or closes an electrical circuit as a result of the movement it receives from the pressure sensing element.

Explosion-Proof Switch

A UL listed switch capable of withstanding an internal explosion of a specified gas without igniting surrounding gases.

F

Factory Set

A pressure switch design that can be set only at the factory to customer’s requirements.

Field Adjustable

A pressure switch design that provides for adjustment of set points in the field.

H

Hermetically Sealed

An enclosure completely sealed from escaping or entry of gases or liquids. All joints are soldered or welded to ensure sealing integrity. Hermetically sealed electrical assemblies are metal to metal or glass to metal infusion.

Hysteresis

See Deadband.

M

Maximum System Pressure

Maximum continuous pressure which may be applied to any switch without causing permanent degradation.

N

Normally Closed (N/C)

Provide a normally closed circuit when actuator is in free position.

Normally Open (N/O)

Provide a normally open circuit when actuator is in free position.

P

Pressure Sensing Element

The portion of the pressure switch that is in contact with the media and moves as a result of a change in pressure of the media.

Pressure Switch

An electromechanical device that upon the increase or decrease of pressure, opens or closes an electrical switching element at a predetermined set point.

Proof Pressure

Maximum momentary pressure including surges, which may be applied to any switch without causing permanent degradation.

R

Rise Rate or Ramp Rate

The rate at which the pressure will increase in a unit of time.

S

Set Point

See Actuation Point.

Single Pole Single Throw (SPST)

Continuity of circuit is only possible through one leg of circuit.

Single Pole Double Throw (SPDT)

Continuity of circuit is possible through either/both legs of circuit but not at the same time.

Surge Pressure

A transient pressure varying in amplitude, frequency and duration.

W

Wetted Parts

Components of a pressure switch that are directly exposed to the media.