Accuracy
The limit of deviation from the set point of a pressure or vacuum switch. It is usually defined in either pounds per square inch, or percentage of full scale.
Actuation Value
The difference between the set point and reset point.
Deadband
The difference between the increasing and decreasing readings when the switch is operated between set point and reset point.
Electrical Switching Element
Opens or closes an electrical circuit in response to movement from the pressure or vacuum sensing element. Single pole, double throw (SPDT) snap action switches are standard, may be used as single pole, single throw (SPST). NO/NC circuitry is selectable, but must be specified at order placement.
Hysteresis
The difference in pressure or vacuum switch response to increasing and decreasing pressure or vacuum.
Normally Closed Switching Element
Current flows through the switch until broken by a pressure or vacuum change.
Normally Open Switching Element
No current flows through the switch until contact by a pressure or vacuum change is made.
Pressure, Absolute
A pressure scale based on PSIA “0” or a perfect vacuum.
Pressure, Ambient
The pressure immediately surrounding a pressure switch, usually but not necessarily, atmospheric gauge pressure.
Pressure, Atmospheric
The pressure caused by the actual weight of the earth’s atmosphere. At sea level atmospheric pressure equals 14.7 psi, 30 inches of mercury or 408 inches of water, above absolute “0” (“0” PSI).
Pressure, Differential
The arithmetic difference between two pressures. The term is correctly applied to “differential” pressure switches that detect variations in a fixed difference between two pressures.
Pressure, Gauge
Atmospheric pressure used as zero reference point so there is no compensation for changes in barometric pressure.
Pressure, Proof
Maximum pressure which can be applied to a pressure switch without causing irreparable damage. It is usually 150% of the pressure sensing element’s rated maximum system pressure.
Pressure, System
Normal system pressure level not including surges or spikes.
Pressure Sensing Element
The portion of the pressure switch that moves with a change in system fluid pressure.
Pressure Switch
An instrument that converts a pressure change to an electrical function.
Repeatability
The ability of the switch to actuate repeatedly at the desired set point within sensor tolerance.
Reset Point
After the pressure has reached set point and operated the electrical switch, it must return to the reset point before the electrical switch returns to its original position.
Set Point
The exact point at which the electrical switching element functions. This is generally expressed in PSI, inches of mercury or PSIA.
Vacuum
Gauge pressure less than ambient pressure using ambient pressure as a reference.