Metrology Glossary – P

At J.A. King, we strive to educate our team and our customers so we can all make informed decisions and improve quality. Having information at our fingertips is the best way to do that. We have compiled a list of the most common terminology within the precision measurement industry, backed by our experts with years within our industry.


Precision Measurement Glossary of Terms

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Panel Meter

An instrument that displays an input signal in either a digital or analog form

Parallax

The seeming displacement of an object and its background when viewed from two different points of observation. A common source of error when reading analog gauges.

Parallel Circuit

A parallel circuit is a closed circuit in which the current divides into two or more paths before recombining to complete the circuit. Each load connected in a separate path receives the full circuit voltage, and the total circuit current is equal to the sum of the individual branch currents.

Parallel Communications

A method of conveying multiple binary digits (bits) simultaneously. For example, an 8-bit parallel channel will convey eight bits (or a byte) simultaneously, whereas a serial channel would convey those same bits sequentially, one at a time.

Parity

A process that ensures accurate data transmission between nodes. A parity bit is added to the end of the original data bits to create an even or odd number.

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.

pH

A figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acid and higher values more alkaline.

pH Meter

A scientific instrument used to measure the hydrogen-ion activity in water-based solutions to determine the acidity or alkalinity of the solution.

Phase

In electronic signaling, phase is a definition of the position of a point in time (instant) on a waveform cycle. A complete cycle is defined as 360 degrees of phase. Phase can also be an expression of relative displacement between or among waves having the same frequency.

Phase Angle

An expression of relative displacement between or among waves having the same frequency.

Pin Gage

A small length of steel with known dimensions used to compare hole and slot dimensions to specific tolerances.

Pipette

A calibrated glass tube drawn to a fine bore at one end, filled by sucking liquid into the bulb, and used to transfer or measure known volumes of liquid

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.

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.

Poise

A counterweight used to balance a scale

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 are used. If there is voltage unbalance, only the 3 element is suitable.

Port (Electronics)

A place where different devices connect in a circuit and signals can be introduced or taken away

Positive Temperature Coefficient

In Resistance Temperature Detectors (RTD’s), the increase in resistance value with a corresponding increase in temperature.

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

Potentiometer

A resistor with an adjustable voltage divider.

Potted Cell

A load cell that is protected well so it may perform in harsh environments

Pounds per Square Inch (PSI)

A unit of measure defined by the pressure created when one pound-force is applied over a surface area of one inch.

Pounds per Square Inch Absolute (PSIA)

A measurement of pressure measured relative to a vacuum rather than the atmosphere

Pounds per Square Inch Gauge (PSIG)

A measurement of pressure measured relative to the atmosphere rather than a vacuum

Power Factor

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

Power Supply

A device that supplies electric power to an electric load.

PPM (Parts Per Million)

Just as per cent means parts of a hundred, parts per million defines parts of a million. Often used in measurement to annotate very small percentages (0.0001% = 1ppm).

Precision

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.

Pressure Gauge

Any of a variety of instruments used to indicate pressure. Pressure gauges may be analog or digital and may have manufacturer-specified accuracy or meet accuracy classes defined in ASME-B40.100.

Pressure Relief Valve

Used in hydraulic systems to limit the system pressure to a specific set level. If this set level is reached, the pressure relief valve responds and feeds the excess flow from the system back to a reservoir.

Pressure Transducer

Is a transducer that converts pressure into an analog electrical signal.

Pressure Transmitter

A variety of pressure transducer that measures pressure in a liquid, fluid, or gas and transmits the electronic output to a computer or display at a remote location. Typically used in industrial environments to monitor process machinery.

Pressurization

The act of increasing the pressure in an enclosure above the atmospheric pressure outside the enclosure.

Primary Axis

The imaginary line that the load should be placed on. Usually runs through the center of the load cell

Process Calibrator

A single device containing a variety of instruments used for calibrating process instruments such as pressure gauges or transducers and thermocouple or RTD temperature controllers.

Process Meter

Any of a variety of instruments designed to measure, display, alarm, and control a wide range of process variables, such as 4-20 mA and 0-10 V analog inputs.

Protection Device

Device installed with the aims of protection of assets and ensuring continued supply of energy. Switchgear is a combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment.

Pneumatic Torque Tool

A planetary torque multiplier or a gearbox that is mated to a pneumatic air motor. At the end of the gearbox is a reaction device that absorbs torque to ensure proper torque at the joint.

Pulse Torque Tool

Rotary torque tools which apply torque in increments rather than in one continuous effort. This type of torque application is also known as discontinuous drive.

Purging

Supplying a steady flow of clean air into a closed area to get rid of any flammable or hazardous gas

Push-Button Auto Zero (PAZ)

A button that when pushed balances the scale to display 0 even if something is on it


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