TERMINOLOGY

TECHNICAL TERMS

ABSOLUTE PRESSURE TRANSDUCER : A transducer that has an internal reference chamber sealed at or close to 0 psia (perfect vacuum) which provides electrical output pressure been applied.

ACCURACY : The combined error of nonlinearity, repeatability and hysteresis in terms of percent of full scale output.

BFSL : BFSL means Best fit straight line. BFSL takes all the data points from the curve and describes a straight line through these data points such that the deviation between the curve and the straight line is at a minimum. The sensitivity of a sensor ideally should be a straight line but it often has some small non-linearity associated with it.

BRIDGE : A Wheatstone bridge configuration consists of four active strain gauges.

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

CALIBRATION : The comparison of transducer outputs against the outputs of a reference standard.

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 distance a diaphragm moves at the center between no-load and rated load conditions.

DIAPHRAGM : The sensing element which is deformed when pressure is applied.

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

FULL SCALE : Rated Capacity.

FULL SCALE OUTPUT : The algebraic difference between the minimum output and the rated capacity.

GAGE PRESSURE : The pressure above (or below) atmospheric is a gage pressure. Represents positive difference between measured pressure and existing atmospheric pressure.

GAGE PRESSURE TRANSDUCER A transducer which measures pressure relative to the atmospheric pressure.

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 continous cycle. The deviation of loading and unloading readings are expressed as a percent of full scale.

INPUT IMPEDANCE : 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 RESISTANCE : The DC resistance expressed in ohms measured between any electrical connector pin or lead wire and the transducer body or case.

LINEARITY : 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 measurandonly.

LINE PRESSURE : The maximum pressure in the pressure vessel or pipe for differential pressure measurement

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

LOAD BUTTONS : The Spherical shape of the top surface of a loadcell where the load is applied.

MEASURAND MEDIA : The physical quantity, property, or condition which is measured. ( eg.: load, weight, pressure )

OUTPUT : The electrical signal measured at the output terminals when given input signal 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, SAFE : The maximum pressure or load which may be applied to the transducer without causing a permanent change in the performance specifications. Acceptable safe limit is 150% of rated capacity.

PSI : Pounds per square inch.

PSIA : Pounds per square inch absolute.

PSID : Pounds per square inch differential.

PSIG : Pounds per square inch gage.

RANGE : Range is the measurand 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.

REPEATABILITY : The ability of a transducer to reproduce output readings when the same consecutive measurand value is applied to it, 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 smallest change in input which produces a change in the output signal.

SENSING ELEMENT The part of the transducer which directly reacts in response to the measurand or has direct contact with the measuring medium.

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

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.

STRAIN GAUGE : A sensing element for converting force, pressure, etc. into an electrical signal.

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.

TEMPERATURE EFFECT ON SPAN : The change in rated output due to a exchange in ambient temperature. Usually expressed as +/- a percentage change in rated output per degree C change in ambient temperature, over the compensated temperature range.

TEMPERATURE EFFECT ON ZERO : The change in zero balance due to a exchange in ambient temperature. Usually expressed as +/- a percentage change in rated output per degree C change in ambient temperature, over the compensated temperature range.

TRANSDUCER : A device that converts energy from one form to another. The term is generally, applied to devices that take physical phenomenon and convert it to an electrical signal.

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

TRUE GAUGE : A true gauge transducer differs from a standard gauge because it has a second diaphragm. The additional diaphragm seals the strain gauges and element in a hermetic chamber, keeping moisture and potentially corrosive gases out. Wet or dry atmospheric pressure is vented to the back side of the second diaphragm to reference barometric changes on the sensing element.

WET / DRY DIFFERENTIAL : A differential presssure 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 presssure 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 measuring 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.