GLOSSARY

Terminology:

Accuracy (Repeatability): Accuracy is the maximum allowable set point deviation of a single pressure or temperature switch under one given set of environmental and operational conditions.

Actuation Point and Deactuation Point: The actuation point (sometimes called set point) is the exact point at which the electrical circuit controlled by the switching element is opened (or closed) on increasing pressure or temperature. The deactuation point is the opposite of the point at which the electrical circuit is closed (or opened) on decreasing pressure or temperature.

Adjustable Range: It is the range within which a switch can be set from lowest to highest set point.

Bimetal Temperature Switch: A temperature sensing device that contains a bimetallic strip. It has a specified temperature set point for which the switch will open or close the circuitry.

Blade Contact: A pressure switch that is not operated by a microswitch, but rather the circuitry is opened or closed through a piece of metal that bridges the two terminals.

Dead Band Differential: Sometimes referred to as "hysteresis", is the change in pressure between the actuation and deactuation set points.

Diaphragm: The membrane of flexible material (Buna, EPDM, Viton®), which is deflected by input pressure.

Field Adjustable: A sensor which has been designed to permit adjustment or calibration of set points in field applications.

Fluid: In engineering terms, a liquid or gas which tends to conform to the shape of its container, and which alters its shape in response to applied force.

Gauge Pressure: A form of differential pressure measurement which uses atmospheric pressure (14.7psia) as the zero reference.

Gold Contacts: Gold switching elements provide high corrosion resistance and high reliability when switching low voltage circuits.

Impedance: In a circuit, the opposition to flow of alternating current, consisting of ohmic resistance, inductive reactance, and capacitive reactance.

Inductive Load: Load from electrical devices which are made of wound or coiled wire. Current passing through the windings creates a magnetic field which produces mechanical work. When an inductive circuit is switched open, energy stored in the coil can reverse flow, sparking at the switch contact surfaces.

Maximum System Pressure: Rated pressure above the normal system pressure, including surges or spikes.

Normally Closed Switching Element: Is one in which the terminals are wired so that current can fl ow through the switching element until pressure is applied to open the electrical circuit.

Normally Open Switching Element: Is one in which the terminals are wired so that no current can fl ow through the switching element until the pressure is applied to close the electrical circuit.

Pressure Range: Minimum and maximum pressure for which a sensor has been calibrated or specified.

Pressure, Proof: Proof Pressure (normally 1-1/2 times system pressure) is the maximum static pressure which can be applied to any switch without causing permanent degradation.

Pressure Sensing Element: That portion of the pressure switch that is in contact with and moves as a result of a change in pressure of the fluid. The most common type of pressure sensing elements are diaphragms, bellows, bourdon tubes, and pistons.

Pressure Switch: An instrument that upon the increase or decrease of a pressure or vacuum, opens or closes one or more electrical switching elements at a predetermined actuation point (setting).

Reed Switch: Is an electrical switch operated by an applied magnetic field. It consists of a pair of contacts, either normally open or normally closed, in a hermetically sealed glass tube.

Resistive Load: Load from devices which use electrical resistance to produce heat or light. Restive loads cause current to flow in only one direction through a circuit.

Set Point: The point at which motion of the pressure or vacuum or temperature sensing element causes the switch to function.

Single Pole Double Throw (SPDT): A SPDT switching element has one normally open, one normally closed and one common terminal. Three terminals mean that the switch can be wired with the circuit either normally open (N/O) or normally closed (N/C) or both.

Snap-Action Switch: A mechanically operated electric switch which, once its actuator has reached its operating (or release) point, immediately transfers to its opposite position without further travel of the actuator.