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Motorola Sensor Device Data
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Glossary of Terms
Absolute Pressure Sensor
A sensor which measures input pressure in relation to a zero pressure (a total vacuum on one side of
the diaphragm) reference.
Analog Output
An electrical output from a sensor that changes proportionately with any change in input pressure.
Accuracy — also see
Pressure Error
A comparison of the actual output signal of a device to the true value of the input pressure. The various
errors (such as linearity, hysteresis, repeatability and temperature shift) attributing to the accuracy of
a device are usually expressed as a percent of full scale output (FSO).
Altimetric Pressure
Transducer
A barometric pressure transducer used to determine altitude from the pressure-altitude profile.
Barometric Pressure
Transducer
An absolute pressure sensor that measures the local ambient atmospheric pressure.
Burst Pressure
The maximum pressure that can be applied to a transducer without rupture of either the sensing ele-
ment or transducer case.
Calibration
A process of modifying sensor output to improve output accuracy.
Chip
A die (unpackaged semiconductor device) cut from a silicon wafer, incorporating semiconductor cir-
cuit elements such as resistors, diodes, transistors, and/or capacitors.
Compensation
Added circuitry or materials designed to counteract known sources of error.
Diaphragm
The membrane of material that remains after etching a cavity into the silicon sensing chip. Changes
in input pressure cause the diaphragm to deflect.
Differential Pressure Sensor
A sensor which is designed to accept simultaneously two independent pressure sources. The output
is proportional to the pressure difference between the two sources.
Diffusion
A thermochemical process whereby controlled impurities are introduced into the silicon to define the
piezoresistor. Compared to ion implantation, it has two major disadvantages: 1) the maximum impuri-
ty concentration occurs at the surface of the silicon rendering it subject to surface contamination,
and making it nearly impossible to produce buried piezoresistors; 2) control over impurity concentra-
tions and levels is about one thousand times poorer than obtained with ion implantation.
Drift
An undesired change in output over a period of time, with constant input pressure applied.
End Point Straight Line Fit
Motorola’s method of defining linearity. The maximum deviation of any data point on a sensor output
curve from a straight line drawn between the end data points on that output curve.
Error
The algebraic difference between the indicated value and the true value of the input pressure.
Usually expressed in percent of full scale span, sometimes expressed in percent of the sensor output
reading.
Error Band
The band of maximum deviations of the output values from a specified reference line or curve due
to those causes attributable to the sensor. Usually expressed as “
±
% of full scale output.” The
error band should be specified as applicable over at least two calibration cycles, so as to include
repeatability, and verified accordingly.
Excitation Voltage (Current) —
see Supply Voltage (Current)
The external electrical voltage and/or current applied to a sensor for ts proper operation (often referred
to as the supply circuit or voltage). Motorola specifies constant voltage operation only.
Full Scale Output
The output at full scale pressure at a specified supply voltage. This signal is the sum of the offset signal
plus the full scale span.
Full Scale Span
The change in output over the operating pressure range at a specified supply voltage. The SPAN of
a device is the output voltage variation given between zero differential pressure and any given
pressure. FULL SCALE SPAN is the output variation between zero differential pressure and when the
maximum recommended operating pressure is applied.
Hysteresis — also see Pressure
Hysteresis and Temperature
Hysteresis
HYSTERESIS refers to a transducer’s ability to reproduce the same output for the same input,
regardless of whether the input is increasing or decreasing. PRESSURE HYSTERESIS is measured
at a constant temperature while TEMPERATURE HYSTERESIS is measured at a constant pressure
in the operating pressure range.
F
Freescale Semiconductor, Inc.
n
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