Glossary of Terms - P


The seeming displacement of an object and its background when viewed from two different points of observation.

Peak Demand (maximum RMS power)

The highest average load during a specified time interval (kW).

Peak Hold

An instrument function that permits retaining and displaying the peak value momentarily reached by a pulse or other brief signal under measurement.


Time relationship between current and voltage in AC circuits.

Phase Angle

The difference in time by which the voltage wave lags or leads the current wave in an AC circuit.

Pivot and Jewel

Method of suspending the moving coil or moving iron vane in a magnetic field, in analog meters. The movable element is equipped with two metal pivots that engage glass or synthetic jewel cup bearings. In most designs, the bearings are spring-backed to prevent dislodging of the pivots by shock or vibration.


A Special high output/high temperature platinum alloy thermocouple (Trademark of Englehard Industries). Platinel 1813 vs. Platinel 1503 has a DMF output of 0-51 mV over span of 32°F to 2372°F. Composition is gold, platinum and palladium. Usual diameter is "0.020" per lead.

Platinum Resistance Thermometer (PRT)

A resistance temperature detector (RTD) that uses platinum as the metal conductor whose electrical resistance changes as a function of temperature.

Polyphase Wattmeter

This wattmeter consists of 2 or 3 single-phase wattmeters mounted in the same package. The watt sensing elements can be electronic transducers or analog dynamometers. A dual element wattmeter will measure power in a 3 phase 3-wire system regardless of power factor, voltage or current variations between phases. Most common analog dynamometer forms are 2, 2-1/2, or 3 element types. In 4-wire circuits with the 4th wire carrying current, the 2-1/2 or 3 element types is used. If there is voltage unbalance, only the 3 element is suitable.

Positive Temperature Coefficient

Resistance increases positively with temperature increases in RTDs as against negative temperature coefficient in most thermistors.

Potential EMF

The relative voltage at a point in a circuit or in space with respect to some reference point.

Potential Transformer

An instrument transformer used to step down high voltage potentials to lower levels acceptable for the input of electrical test instruments

Power Factor

The ratio of consumed power (watts) to apparent (volt-ampere) power in an AC circuit. Expressed in decimal form.


The abbreviation for "parts per million," sometimes used to express temperature coefficients. For instance, 100 ppm is identical to 0.01%.


An indication of the number of distinguishable valid alternatives presented by an instrument scale or readout for obtaining a measurement. The greater the number of (analog) graduations or (digital) significant figures, the higher the precision, provide that the subdivisions have been meticulously achieved. Precision and accuracy are independent, but interrelated characteristics. A high degree of precision implies a high degree of accuracy, but does not assure it. On the other hand, a high degree of accuracy requires a high degree of precision.

Process Meter

A panel meter with sizeable zero and span adjustment capabilities, which can be scaled for readout in engineering units for signals such as 4029 mA, 10-50 mA and 1-5V.

Protecting Tube

A closed-end tube designed to isolate and protect a temperature sensor from the adverse effects of an environment. May incorporate means for mounting, but not primarily intended for pressure-tight attachment to a vessel.


Pressure gauge using vacuum as the reference (zero on scale represents vacuum).


Pressure gauge using ambient air pressure as the reference (zero on scale represents ambient pressure).