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 IMPEDANCEand 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 ower 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.
DYNAMIC PRESSURE:
See
IMPACT PRESSURE.
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 ELEMNT:
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.
STANDARD PRESSURE:
Pressure of one normal (standard) atmosphere, defined (in the United States and
some other countries) as 101.325 kPa (14.696 psia).
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 COEFFICIENT:
The percentage change in the sensitivity of a transducer as a result of a
change in the operating temperature of the transducer (expressed as percent per
degree [%/ºF]).
TEMPERATURE COMPENSATED:
The range of temperature over which a transducer can operate up to full scale
and still meet all specifications. 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.
