Glossary of Transducer Terms

Acceleration Error

The maximum difference, at any measured value within the specified range, between output reading taken with and without the application of a specified constant acceleration along specified axes.

Ambient Conditions

The conditions of the medium surrounding the transducer. This includes temperature, humidity, pressure, radiation and vibration.

Absolute

The pressure measured relative to vacuum.

Absolute Pressure Transducer

A pressure transducer or pressure sensor that has an internal reference chamber sealed at or close to 0 psia (full vacuum) and normally provides increasing output voltage for increases in pressure.

Acceleration

A vector quantity equal to the time rate of change velocity, with respect to a reference system.

Acceleration Sensitivity

Acceleration error expressed in percent of full-scale output per g. The term is indicative of the response of a system due to the acceleration input.

Accelerometer

A device that measures the acceleration of moving body and translates it into a corresponding electrical quantity.

Accuracy

The extent to which the measured value deviates from the true value of the measured or the combined error of nonlinearity, repeatability, and hysteresis expressed as a percent of full scale output.

Active Element

A device capable of controlling voltages/ currents, to produce a gain or switching action in circuit.

Amplifying Transducer

A transducer with an integrally packaged amplifier.

Analog Output

Transducer output which is a continuous function of the measured (except as modified by the resolution of the transducer

Attitude

The relative orientation of a vehicle or object represented by its angles of inclination to three orthogonal reference axes.

Attitude Error

The error due to the orientation of the transducer relative to the direction in which gravity acts upon the transducer.

Axial Load

A load applied along or parallel to and concentric with the primary axis.

Bellows

A mechanical element of generally cylindrical shape with cylindrical walls having deep convolutions.

Best Fit Straight Line

A line midway between two parallel straight lines close together and enclosing all output versus measured values, on a calibration curve.

Bondable Transducer

A transducer which is designed to be permanently mounted to a surface by means of adhesives.

Bonded Strain Gauge

A resistance train transducer, permanently attached over the length and width of its active element.

Bourdon Tube

A pressure sensing element consisting of a twisted or curved tube of noncircular cross section which tends to get straightened on the application of internal pressure.

Bridge

A Wheatstone bridge configuration utilizing four active strain gages.

Bridge Resistance

The nominal value of the individual legs that make up a complete Wheatstone Bridge.

Burst Pressure Rating

Maximum pressure which may be applied to the sensing element or the case of a transducer, without rupture of either the sensing element or the case.

Calibration

A test during standard values measured are applied to the transducer and the corresponding output reading are compared with the standard values e.g., The comparison of transducer voltage outputs against the outputs of a reference standard.

Calibration Curve

A graphic representation of the calibration record (plot of calibration of the data).

Calibration Cycle

The application of known values of the measured and calibration of the readings of the corresponding output values, over the full (or specified) portion of the range of a transducer, in an ascending or descending order.

Calibration Traceability

The relation of a transducer calibration, through a specified step by step process, to an instrument or group of instruction calibrated by a national standard agency.

Calibration Uncertainty

The maximum calculated error in the output values shown in a calibration record, due to causes not attributable to the transducer.

Capsule

A pressure-sensing element consisting of two corrugated metallic diaphragms joined along their circumference.

Centre Of Seismic Mass

The point within an acceleration transducer where acceleration forces are considered to be summed.

Compensated Temperature Range

The operating temperature range of a transducer incorporating temperature compensation.

Compensation

The utilization of supplemental device, materials, or process to minimize known sources of error.

Conduction Error

The error in a temperature transducer due to heat conduction between the sensing element and the mounting of the transducer.

Conformance, Conformity

The closeness of a calibration curve to a specified curve.

Continuous Rating

The rating applicable to a specified operation for a specified uninterrupted length of time.

Creep

A change in output occurring over a specified period of time with the measured applied and all the environmental conditions and other variables remaining constant.

Critical Damping

The degree of damping required to give the most rapid transient response without overshoot or oscillation. It lies between underdamped and over damped conditions.

Cross Sensitivity

The maximum sensitivity of a transducer to a specified value of transverse measured applied in a direction orthogonal to the primary axis, expressed in percent of the sensitivity in the designed major axis.

Damping

The energy dissipating characteristics which together with a natural frequency determines the limit of frequency response and the response characteristics of a transducer. Any action or influence that extracts energy from a vibratory system in order to suppress the vibration or oscillation.

Damping

The reduction of response at the resonant frequency through the use of a damping media such as oil. Usually specified as the ratio of critical damping.

Damping Factor

The ratio of amplitude of any one series of damped oscillations to that of the following one- also called decrement.

Damping Ratio

The ratio of the degree of actual damping to the degree of damping required for critical damping.

Damping-Magnetic

Damping effect (by use of current in electrical conductors) by changes in magnetic fields.

Damping-Viscous

Damping effected by use of the viscosity of liquids and gases.

Dead Band

The range of values over which a measured variable can change without affecting the output.

Dead Time

The time during which a device or a system is insensitive after receiving a stimulus, to any other impulse or stimulus.

Dead Volume

The total volume of internal cavity between the sensing element and the external portion of the pressure port of a pressure transducer e.g., 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 distance a diaphragm moves at the center between no-load and rated load conditions.

Diaphragm

A sensing element consisting of a thin flexible circuit plate which can be actuated by a pressure differential applied across the plate.

Diaphragm

The sensing membrane which is deformed when pressure is applied.

Differential Transformer Transducer

A transducer in which movement of the ferromagnetic core of a transformer varies the output voltage across two series opposing secondary windings.

Directivity

The solid angle or the angle in a specified plane over which sound energy or radiant energy, impinging on a transducer, is measured.

Displacement

The extent of special distance through which an object or a point is moved.

Displacement Transducer

A transducer that convert a linear or angular movement into a corresponding electrical signal.

Drift

The random change in output under constant measured and normal operating conditions.

Dynamic Calibration

A calibration during which the measurement varies with time in a specified manner and the output is recorded as a function of time.

Dynamic Characteristics

Characteristics of a transducer which relate to its response to variations of the measurand with time.

Elastic Member

The element or element within the transducer to which a number of sensing elements are attached.

Electro-Magnetic Transduction

The conversion of the measurand into an induced voltage in a conductor by a change in magnetic flux without any excitation.

End Point

The output at the specified upper or lower limit of the range.

End Point Line

The straight line between the end points.

Environmental Conditions

Specified external conditions (shock vibration temperature, and humidity) to which a transducer may be exposed during operation, storage, or shipping.

Error

The algebraic difference between the indicated or observed value and the true value of the measurand.

Error-Band

The band of maximum deviation of output values from a specified reference line or curve, due to those causes attributable to the transducer, as measured over two consecutive calibration cycles.

Error-Curve

A graphical representation of error obtained from a specified number of calibration cycles.

Excitation (Electrical)

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

Fatigue Life

The number of load cycles at a specified measurand value, before deterioration of electrical characteristics occurs.

Field Of View

The solid angle or angle in a specified plane over which radiant energy incident on a transducer is measured within stated to tolerances.

Flow Meter

A device that measures/ indicates the rate of flow of a liquid or gas.

Flow Rate

The time rate of motion of a fluid quantity unit time.

Fluid

A gas or liquid.

Fluid Damping

See viscous damping.

Flush Diaphragm

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

Force

The vector quantity necessary to cause a change in momentum.

Frequency Response

The range of frequencies over which the faithful reproduction of the measurand is obtained / The range of frequencies over which the transducer voltage output will follow the sinusoidal varying mechanical input within specified limits.

Frequency, Natural

The frequency of free oscillations of the sensing element of a fully assembled transducer.

Frequency, Resonant

The measurand frequency at which the transducer responds with maximum output amplitude.

Friction Error

The maximum change in output before and after minimizing friction within the transducer by dithering.

Friction -Free Calibration

Calibration under conditions minimizing the effect of static friction obtained by dithering.

Full Scale

See Rated Capacity.

Full Scale Output

The algebraic difference between the minimum output (normally zero) and the rated capacity.

Full-Scale Output

The algebraic difference between the end points of the range of the device.

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.

Gage Pressure Transducer

A transducer which measures pressure relative to the atmospheric pressure.

Gauge Factor

A measure of the ratio of the relative change of resistance to the relative change in length of a resistive strain transducer (strain gauge).

Gauge Pressure

Pressure measured relative to ambient pressure.

Gyro (Gyroscope)

An initial device having a spinning mass, the tendency of which is to remain fixed in its angular relationship to inertial space.

Hall Effect

The development of a transverse electric potential gradient between the two edges of a current carrying conductor or semiconductor whose faces are perpendicular to an applied magnetic field.

Harmonic Distortion

The distortion in a transducer's in the form of harmonious other than the fundamental component.

Harmonic Motion

A motion whose instantaneous amplitude varies sinusoidal with time.

Heat Conduction

The transfer of heat energy by diffusion through solid material or through stagnant fluids.

Heat Convection

The transfer of heat energy by the movement of a fluid between two points.

Heat Flux

The time rate flow of heat energy per unit area.

Heat Radiation

The transfer of heat energy by electromagnetic waves.

Hysteresis

The maximum difference between output readings for the same measured 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.

Hysteresis, Thermal

The maximum difference in output, at a given measurand value within the specified range and at a given temperature when this temperature is approached in the increasing and in the decreasing portion of a temperature cycle whose maximum temperature is substantially beyond the given temperature.

Impact Pressure

The pressure in moving fluids exerted parallel to the direction of flow due to the velocity of the flow.

Inductive Transduction

Conversion of the measurand into a change of the self-inductance of a single coil.

Input Impedance

The impedance presented to the excitation source, measured across the excitation terminals of a transducer / The resistance measured across the excitation terminals of a transducer at room temperature, with no load applied, and with the output terminals open-circuited.

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. / The DC resistance measured between specified insulated portions of a transducer (when a specified DC voltage is applied).

Integrating Transducer

A transducer whose output is a time integral function of the measurand.

Intermittent Rating

The rating applicable to a specified operation over a state number of time intervals of specified duration.

Ionizing Transduction

Conversion of the measurand into a change in ionizing current, such as that through a gas between two electrodes.

Jerk

A vector unit that specified the time rate of change of acceleration.

Lead Impedance

The complex impedance presented to the output terminals of a transducer by the associated external circuitry or load.

Leakage Rate

The maximum rate at which a fluid at a specified pressure in leaking through specified scaled portion of transducer.

Least Square Line

The straight line for which the sum of the squares of the residual deviation is minimized.

Life Cycling

The specified minimum number of full range excursion s or specified partial changing its performance beyond specified tolerances.

Life, Operating

The specified minimum length of time over which the specified continuous or intermittent rating of a transducer applies without changing its performance beyond specified tolerances.

Life, Storage

The specified minimum length of time over which a transducer can be exposed to a specified storage condition without changing its performance beyond specified tolerances.

Line Pressure

The maximum pressure in the pressure vessel or pipe for differential pressure measurement.

Linearity

The maximum deviation of any calibration point, obtained for either increasing or decreasing input, from the best fit straight line having overall minimum deviation. / The maximum deviation of the calibration curve from a straight line between zero and full scale, expressed as a percent of full scale output and measured on increasing measured only.

Linearity, Endpoint

Linearity, referred to a straight line between the end points.

Linearity, Independent

Linearity referred to the best straight line passing through zero.

Linearity, Least Square

Linearity referred to a straight line for which the sum of the squares of the residuals is minimized.

Linearity, Terminal

Linearity, referred to the terminal line.

Load

The weight, torque, or force applied to the transducer.

Load Buttons

The spherical like shape of the top surface of a load cell where the load is applied.

Load Cell

The device, which generates an output signal proportional to the applied force or weight.

Loading Error

An error introduced due to the effect of the load impedance on the transducer output.

Magnetoresistive Effect

The change in the resistance of a conductor or semiconductor due to the application of a magnetic field.

Magnetostriction

The change in dimension of a ferromagnetic object when the object is placed in a magnetic field.

Mass

The quantity of matter in body. Mass is a measure of inertia and determines resistance to acceleration, independency of gravitation force.

Mean Output Curve

The curve through the mean values of output during any one-calibration cycle of a different specified number of calibration cycles.

Measurand

The physical quantity, property, or condition that is to be measured.

Measurand Medium

The medium, which comes in contact with the sensing element.

Measured Media

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

Mechanical Impedance

The complex ratio of force to velocity during simple harmonic motion.

Motion

The change in position of a body or point with respect to a reference system.

Mounted Resonant Frequency

The frequency at which the internal spring/mass system of an accelerometer resonates, producing a 90º phase shift in output signal vs. applied acceleration.

Mounting Error

The error resulting from mechanical deformation of the transducer caused by mounting the transducer.

Non-Linearity

(See linearity).

Null

A condition of balance, which results in a minimum absolute value of output.

Output

The electrical quantity (useful energy) produced by a transducer. The magnitude is a function of the applied measurand.

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 measured applied, and with the excitation terminals open-circuited.

Output Noise

The unwanted component (typically of broad frequency spectrum) of the output of a transducer.

Output Rated

The algebraic difference in value between the outputs at no input and rated input of measurand.

Over Range

(See Overload).

Overload

The maximum magnitude of measurand that can be applied to a transducer without causing a change in performance beyond specified tolerance.

Over range, Safe

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

Overshoot

The amount of output measured beyond the final steady output value in response to a step change in the measurand.

Phase Shift

The phase angle between the output signal and the applied acceleration.

Photoconductive Transduction

Conversion of a measurand into a change in resistance or conductivity by a change in the magnitude of illumination incident upon the material.

Photoemissive Transduction

Conversion of the measurand into a change of emission of electrons due to a change in the incidence of photons on a photocathode.

Photovoltaic Transduction

Conversion of the measurand into a change in voltage generated when a junction between dissimilar materials is illuminated.

Piezoelectric Transduction

Conversion of the measurand into a change in electrostatic charge or voltage generated by certain materials when mechanically stressed.

Piezoresistive Transduction

Conversion of the measurand into a change in the resistance of a conductor or semiconductor by a change in the mechanical stress applied to it.

Potentiometric Transduction

Conversion of the measurand in to a voltage ratio by a change in the position of a movable wiper on a resistance element across which excitation is applied.

Precision

The degree reproducibility among several independent measurements of the same true value under reference conditions.

Pressure

Force acting on a surface measured as force per unit area (this may be absolute pressure, differential pressure, gauge pressure, or reference pressure).

Primary Axis

The axis along which the transducer is designed to be loaded; normally its geometric centerline.

Psi

Pounds per square inch.

Psia

Pounds per square inch absolute.

Psid

Pounds per square inch differential.

Psig

Pounds per square inch gage.

Pull Plate

Load cell attachment which allows tension or compression force to be directed at the center line of a load cell through a threaded center hole.

Pyroelectric Effect

The generation of charge in certain crystals when unequally heated or cooled.

Random Vibration

Non-periodic vibration described only in statistical terms (mean vibration characterized by a normal amplitude distribution) within prescribed limits.

Range

The measured value over which transducer is intended to measure, specified by upper or lower limits.

Range

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

Rated Capacity

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

Recovery Time

The time interval after a specified event after which a transducer again performs within its specified tolerances.

Reference Pressure

The pressure relative tops which a differential pressure transducer is used.

Reference Standard

A transducer or a device whose characteristics are precisely known relative to a primary standard.

Relative Humidity

The ratio of the water vapour pressure actually present to the water vapour required for saturation at a given temperature expressed in percentage.

Reliability

A measure of the probability that a transducer / device will continue to perform within specified limits of error a specified length of time under specified conditions.

Repeatability

The ability of a transducer to reproduce output reading when the same measurand value is applied to it repeatedly under the same environment condition and in the same direction.

Repeatability

The ability of a transducer to reproduce output readings when the same measured 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

The magnitude of discernable (detectable) output changes as the measurand is continuously varied over the range or The smallest change in mechanical input which produces a detectable change in the output signal.

Response Time

The time required for the output of a transducer to reach a specified percentage of its final value as a result of a step change of measurand.

Rise Time

The time required for the output of a transducer to rise from 10% to 90% of its final value.

Sensing Element

That part of the transducer, which responds directly to the measurand.

Sensitive Axis

The axis along which the input measurand is applied or mounted.

Sensitivity

The ratio of the change in transducer output to a corresponding change in the value of the measurand.

Shock

A short non-periodic or transient excitation of a mechanical system.

Shunt Cal (R-Cal)

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

Source Impedance

The impedance presented to the transducer’s excitation terminals by the excitation source.

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.

Stability

The ability of a transducer to retain its repeatability and other characteristics throughout its specified operating life and storage life.

Stagnation Pressure

Sum of the static pressure and the impact pressure in a fluid flow.

Static Calibration

A calibration performed by application of the measurand to the transducer at discrete amplitude intervals.

Static Error Band

The error band applicable are room conditions and in the absence of any vibration shock or acceleration. It is cumulative effect of non-linearity, hysteresis and non-repeatability.

Strain

The deformation in a body or object resulting from a stress measured as the ratio of the dimensional change to the total value of the dimension in which the change occurs.

Strain Gage

A measuring element for converting force, pressure, tension, etc., into an electrical signal.

System Accuracy

Difference between the value as measured on the system and the true value.

Temperature Compensation

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

Temperature Effect On Span

The change in rated output due to a change in ambient temperature. Usually expressed as ± a percentage change in rated output per degree F change in ambient temperature, over the compensated temperature range.

Temperature Effect On Zero

The change in zero balance due to a change in ambient temperature. Usually expressed as ± a percentage change in rated output per degree F change in ambient temperature over the compensated temperature range.

Temperature Error

The maximum change in output at any measured value within the specified range, when the temperature of the transducer is changed from one value to another.

Temperature, Compensated

The range of temperature over which a transducer can operate up to full scale and still meet all specifications.

Temperature, 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.

Terminal Line

A theoretical slope for which the theoretical end points are 0% and 100% of both measurand and output.

Thermal Co-Efficient Of Resistance

The relative change in resistance of a conductor or semiconductor per unit change in temperature over a stated range of temperature.

Thermoelectric Transduction

Conversion of the measurand into a change in e.m.f generated by a temperature difference between the junctions of two selected dissimilar metals.

Threshold

The smallest change in the measurand that produces a detectable change in the transducer output.

Time Constant

The time required for the output of a transducer to rise to 63.2% of its final value as a result of a step change in the measurand.

Torque

The moment of force.

Traceability

The step transfer process by which the transducer calibration can be related to the reference standards.

Transducer

A device, which provides a usable output in response to a specified measurand.

Transducer

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

Transduction Element

The part of the transducer in which the information originates.

Transfer Function

A mathematical relationship between the input and the output expressed as a ratio of two polynomials.

Transient Response

The response of a transducer to step/ fast change in measurand.

Transmitter

A transducer that has a 4-20 mA two wire output.

Transverse Acceleration

Acceleration perpendicular to the sensitive axis of transducer.

Transverse Sensitivity

Signal output as a result of acceleration perpendicular to the sensitive axis. Specified as a percentage of sensitive axis output for equivalent right angle acceleration or as a decimal fraction.

Triboelectric Effect

The generation of electric charge by friction between surfaces.

Velocity

A vector quantity equal to the time rate of change of displacement with respect to a reference system.

Vibration Error

The maximum change in output of a transducer when a specific amplitude and range of frequencies are applied to a specific axis at room temperature.

Warm-Up Period

The period of time, starting with the application of power to the transducer, required to assure that the transducer will perform within specified tolerance.

Wet/Dry Differential

A differential pressure transducer or transmitter that uses a metal diaphragm at the wet port where fluids can be applied, and no diaphragm at the dry port. The dry port exposes the internal circuitry to the medium, so only clean dry gas can be applied to this port.

Wet/Wet Differential

A differential pressure transducer or transmitter that has a metal diaphragm in each pressure port to permit fluid into both ports.

Wetted Parts

The diaphragm and pressure port material that comes in direct contact with the medium (gas, liquid).

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 as a percent of rated 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.

Zero Shifts

A change in output over a specified period of time at specified ambient conditions with input held constant.