Ohmmeter: A device used to measure electrical resistance.
One-to-one repeater: A diaphragm-operated device which detects process pressure and generates an air (or nitrogen) output signal of equal pressure.
Optical isolation: Two networks or circuits in which an LED transmitter and receiver are used to maintain electrical discontinuity between the circuits.
Output settling time: The time required for an analog output voltage to reach its final value within specified limits.
Output signal: A signal delivered by a device, element or system.
Output slew rate: The maximum rate of change of analog output voltage from one level to another.
Overtravel: That part of a stroke which falls between the end of the calibrated range and the travel stop.
Phase: A time-based relationship between a periodic function and a reference.
Phase shift: The angle in degrees between an energizing voltage waveform and an output signal waveform.
Polarity: In electricity, the quality of having two charged poles, one positive and one negative.
Port: A communications connection on an electronic or computer-based device.
Power supply: A separate unit or part of a system that provides power (pneumatic, electric, etc.) to the rest of a system.
Pressure, ambient: The pressure of the medium surrounding a device.
Pressure, design: The pressure used in the design of a vessel or other item of equipment for the purpose of determining the minimum permissible wall thickness or size of parts for a given maximum working pressure (MWP) at a given temperature.
Pressure, maximum working: The maximum permissible operating pressure at a specified temperature. This is the highest pressure to which the device will be subjected during regular use.
Pressure, operating: The actual (positive or negative) pressure at which a device operates under normal conditions.
Pressure, rupture: The burst pressure of a device (determined by testing).
Pressure, static: The steady-state pressure applied to a device.
Pressure, supply: The pressure at which a utility (such as air) is supplied to a device.
Pressure, surge: Operating pressure plus the increment to which a device can be subjected for a very short time during temporary pressure surges caused by such phenomena as pump start-up or valve shut-off.
Pretravel: That part of a stroke which falls below the calibrated range, between zero and the travel stop.
Primary element: An element that converts a measured variable into a force, motion or other form suitable for measurement.
Process: Physical or chemical change of matter or conversion of energy.
Process measurement: The acquisition of information that establishes the magnitude of process quantities.
Programmable logic controller (PLC): Computer-based industrial monitoring and control package with applications mostly in the areas of safety, sequential or logical operations, where control actions are based on equipment and alarm status.
Proportional control: A control mode which generates an output correction in proportion to error (the process variable’s deviation from setpoint).
Proportional-integral-derivative (PID): Also referred to as a 3-mode controller, combining proportional, integral, and derivative control actions.
psia: Pounds per square inch absolute; the unit of pressure used when the zero reference is full vacuum.
psig: Pounds per square inch gauge; the unit of pressure used when the zero reference is the barometric pressure of the atmosphere.