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Glossary

 

Accuracy

The limit of deviation from the set point of the switch. It is normally defined in either points per square inch or percentage of full scale.
 

Actuation Point

See Set Point.
 

Actuation Value

The difference between the set point and the reset point.
 

Adjustable Range

The range between the lowest or highest point, within which the switch can be set. It is normally expressed in PSI, inches of mercury or inches of water column.
 

Deadband

The difference between the increasing and decreasing readings when the switch is operated between set point and reset point.
 

Differential

The mechanical motion lost within the electrical switch element while it reverses itself. This is usually greater in high amperage switches than in low amperage switches.
 

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 it must be specified at order time.
 

Hysteresis

The difference between the increasing and decreasing readings when the switch is operated between set point and reset point.
 

Normally Closed Switching Element

Current flows through the switch until it is broken by a pressure or vacuum change.
 

Normally Open Switching Element

No current flows through the switch until contact is made by a pressure or vacuum change.
 

Pressure, Absolute

A pressure scale based on PSIA "0" or a perfect vacuum.
 

Pressure, Ambient

The pressure immediately surrounding a pressure switch.
 

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 or mercury or 408 inches or water, above absolute "0" ("0" PSIA).
 

Pressure, Barometric

Actual atmospheric pressure in a specific location and altitude. The standard is 29.22 inches of mercury at sea level at 70°F.
 

Pressure, Differential

The difference between a reference pressure and a variable pressure.
 

Pressure, Gauge

Uses atmospheric pressure as a zero reference point so there is no compensation for changes in barometric pressure.
 

Pressure, Maximum System

System pressure including surges or spikes.
 

Pressure, Proof

The 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.
 

Reset Point Range

The difference between the set point and the reset point. It is caused by the hysteresis of the pressure or vacuum sensing element and the differential of the electrical switch.
 

Response Time

The amount of time taken between a change in the pressure of the system and the change in the electrical signal.
 

Set Point

The exact point at which the electrical switching element functions. This is generally expressed in PSI, inches of mercury or inches of water column.
 

Set Point Range

The range within which the switch can be set from the lowest to the highest point, usually expressed in PSI, inches of mercury or inches of water column.
 

Switching Current, Maximum

The maximum amperage load that the electrical switch will carry. Temperature, Ambient - 21° C or 70° F. Also known as "room temperature."
 

Temperature, Shift

A change in switch set point due to changes in surrounding temperature.
 

Vacuum

Gauge pressure less than ambient pressure using ambient pressure as a reference.