Glossary

The vibration monitoring industry has specialized jargon that is commonly used when talking about vibration sensors, accelerometers and associated applications. It's important that you understand common terminology to communicate effectively with vibration monitoring, reliability, condition monitoring and process automation professionals. We hope you find our glossary useful to find specialized terms and definitions used across vibration, condition monitoring and predictive maintenance.

 






ABSOLUTE PRESSURE

The pressure measured relative to a perfect vacuum.

ABSOLUTE PRESSURE TRANSDUCER

A transducer that has an internal reference chamber sealed at or close to 0 psia (full vacuum).

ACCURACY

The ratio of the error to the output or to the full scale output, as specified, expressed in percent.

ATMOSPHERIC PRESSURE

The pressure caused by the weight of the earth’s atmosphere; varies with geographic location, altitude, and weather.

BAROMETRIC PRESSURE

See ATMOSPHERIC PRESSURE.

BEST STRAIGHT LINE

The line parallel to, and centered between, two parallel straight lines enclosing all calibration data points.

BRIDGE

A Wheatstone bridge configuration utilizing four resistive elements.

BRIDGE RESISTANCE

See INPUT IMPEDANCE and OUTPUT IMPEDANCE.

CALIBRATION

The comparison of transducer voltage outputs against the outputs of a reference standard.

COMMON MODE PRESSURE

See LINE PRESSURE.

CONSTANT CURRENT

Electric current independent of either voltage or resistances and fixed at a specific value. A constant current power supply varies its output voltage, up to its maximum compliance voltage, to maintain the fixed current into the load.

DAMPING

The reduction of response at the resonance frequency through the use of a damping medium such as oil. Usually specified as the ratio to the critical damping.

DEAD VOLUME

The volume inside the pressure port of a transducer at room temperature and barometric pressure.

DEFLECTION

The change in length along the primary axis or the distance a diaphragm moves at the center between no-load and rated-load conditions.

DIAPHRAGM

The sensing membrane which is deformed when pressure is applied.

DIFFERENTIAL PRESSURE

The difference in pressure between two measurement points.

ENDEVCO

An acronym for ENgineering DEVelopment COmpany. A leader in developing instrumentation for the sensing of physical phenomena.

EXCITATION, ELECTRICAL

The voltage or current applied to the input terminals of the transducer.

FLUSH DIAPHRAGM

Sensing element is located on the very tip of the transducer (No pressure port).

FREQUENCY RESPONSE

The range of frequencies over which the transducer voltage output will follow a sinusoidally varying mechanical input within specified limits.

FULL SCALE

The maximum measurand that a transducer is designed to measure within its specification.

FULL SCALE OUTPUT

The algebraic difference between the output with zero input and output with full scale input (range) applied.

GAGE PRESSURE

The pressure above (or below) atmospheric. Represents positive difference between measured pressure and existing atmospheric pressure. Can be converted to absolute by adding actual atmospheric pressure value.

HYSTERESIS

The maximum difference between output readings for the same measurand point, one point obtained while increasing from zero and the other while decreasing from full scale. The points are taken on the same continuous cycle. The deviation is expressed as a percent of full scale.

IMPACT PRESSURE

The pressure in a moving fluid which is exerted parallel to the direction of flow, caused by the inertial effects of the mass of the fluid. Also called DYNAMIC PRESSURE or VELOCITY PRESSURE.

INDEPENDENT LINEARITY

Maximum deviation from the linear regression line (least squares fit) for all measured points, expressed as percent of full scale output.

INPUT IMPEDANCE

The resistance measured across the excitation terminals of a transducer at room temperature.

INSULATION (ISOLATION) RESISTANCE

The DC resistance, expressed in ohms, measured between any electrical connector pin or lead wire and the transducer body or case. Normally measured at 50 Vdc.

LINEARITY

The maximum deviation of the calibration curve from a specified straight line expressed as a percent of full scale output and only measured on increasing measurand.

LINE PRESSURE

The maximum pressure in the pressure vessel or pipe for differential pressure measurement. Also called COMMON MODE PRESSURE.

MEASURAND

The physical quantity, property, or condition which is measured. (e.g.: pressure, load, weight, acceleration).

MEDIUM (MEDIA)

The fluid(s) in contact with the diaphragm, the pressure of which is being measured.

NONLINEARITY

Used interchangeably with “linearity.”

NONREPEATABILITY

Used interchangeably with “repeatability.”

OUTPUT

The electrical signal measured at the output terminals which is produced by an applied input to a transducer.

OUTPUT IMPEDANCE

The resistance as measured on the output terminals of a transducer at standard temperature, with no measurand applied, and with the excitation terminals open-circuited.

OVERRANGE

The maximum pressure or load which may be applied to the transducer without causing a permanent change in the performance specifications.

PARTIAL PRESSURE

The pressure which would be exerted by one constituent of a mixture of gases, if it alone were to occupy the same volume as the mixture. See also TOTAL PRESSURE.

PASCAL

Pressure of one Newton (force) per square meter.

PHASE SHIFT

The phase angle between the output and the applied signal.

PRESSURE HEAD

The height of a liquid column at the base of which a given pressure would be developed due to gravity acting on the fluid mass.

PSI

Pounds per square inch.

PSIA

Pounds per square inch absolute.

PSID

Pounds per square inch differential.

PSIG

Pounds per square inch gage.

RANGE

The measurand values, over which a transducer is intended to measure, specified by their upper and lower limits.

REFLECTED OVERPRESSURE

The total pressure that results at the interface when a shock wave traveling in a medium encounters a discontinuity such as a rigid surface or another shock wave.

REPEATABILITY

The ability of a transducer to reproduce output readings when the same measurand value is applied to it consecutively, under the same conditions, and in the same direction. Repeatability is expressed as the maximum difference between output readings as a percent of full scale.

RESOLUTION

A measure of ability to delineate, detail, or distinguish between nearly equal values of quantity. Also referred to as “threshold” – lowest level of valid measurement.

RESPONSE TIME

The time required for the output of a transducer to increase from zero to some specified percentage of its final value when excited by a step change in measurand.

RISE TIME

The time required for the output of a transducer to rise from 10% to 90% of its final value as a result of a step change of measurand.

SEALED (or SEALED GAGE) PRESSURE

Pressure measured with reference to the pressure in a sealed container; the container is usually within the sensor.

SENSING ELEMENT

The part of the transducer which reacts directly in response to the measurand.

SENSITIVITY

The ratio of change in transducer output to a change in the value of the measurand. Specified sensitivity is usually averaged over the full scale range of the measurand.

SHUNT CALIBRATION

The change in electrical output caused by placing a fixed resistor between the appropriate transducer terminals. Used “in the field” for quick calibration.

S.I. SYSTEM

The international (metric) system of units.

SPAN

The algebraic difference between the limits of the range from zero to full scale.

SPECIFICATIONS

The group of error limits within which each device will operate.

STAGNATION PRESSURE

The sum of the static pressure and the impact pressure. It can be measured at a point where the velocity of the fluid is zero.

STATIC PRESSURE

The pressure of a fluid, exerted normal to the direction along which the fluid flows.

STRAIN GAGE

A measuring element for converting mechanical strain into an electrical signal.

SUPPLY VOLTAGE

See EXCITATION.

TEMPERATURE COMPENSATED

The range of temperature over which a transducer can operate up to full scale and still meet all specifications. Meggitt’s Endevco pressure transducers incorporate temperature compensation.

TEMPERATURE COMPENSATION

The utilization of supplementary devices, materials, or components with the transducer to minimize sources of error caused by changing temperature.

TERMPERATURE, OPERATING

The range of temperature over which a transducer may be safely operated up to full scale without causing failure; but specifications may not be met.

THERMAL SENSITIVITY SHIFT

The change in sensitivity due to a change in ambient temperature. Usually expressed as the maximum percentage change in sensitivity.

THERMAL ZERO SHIFT

The change in zero balance due to a change in ambient temperature. Usually expressed as the maximum percentage change of FSO over the compensated temperature range.

TOTAL PRESSURE

The sum of the pressures (partial pressures) which each gas (in a mixture of gases) would exert were it to occupy the containing vessel alone.

TRANSDUCER

A device (or medium) that converts energy from one form to another. The term is generally applied to devices that take a physical phenomenon (pressure, temperature, humidity, flow, etc.) and convert it to an electrical signal.

VACUUM

Pressure measured below atmospheric pressure and with reference to atmospheric pressure (Negative gage pressure).

VELOCITY PRESSURE

See IMPACT PRESSURE.

ZERO ADJUSTMENTS

Used when “setting up” a transducer to adjust the output signal to zero when zero load/pressure is applied.

ZERO BALANCE

The output signal of the transducer with rated excitation and with no-load applied, usually expressed in millivolts. Also called ZMO and zero pressure output.

ZERO RETURN

The difference in zero balance measured immediately before rated load application of specified duration and measured after removal of the load, and when the output has stabilized.