A wide
variety of sensors (also known as transducers) are used to measure
and acquire a physical property’s value. It is up to the instrumentation
engineer to select the device to meet the environmental, response,
accuracy,
size, and cost specifications for the application. Signal conditioners
serve as the interface of the data acquisition system from the transducers.
Many transducers require ac or dc power (e.g., thermistors, strain
gages,
and linear variable differential transformers - LVDTs) while others generate
signals (tachometers, thermocouples, and piezoelectric strain gages).
They provide excitation (power), network calibration, signal amplification,
and filtering.In airborne data acquisition, sensor output characteristics must be transformed,
filtered, or modified for compatibility with the next stage of the system.
The absolute relationship between the output and the actual property value
of the measurand may vary with time, altitude, pressure, temperature,
etc. Therefore, signal conditioners also incorporate calibration features
to assist in defining the relationships.
A system under test may be
subjected to known physical characteristics and the output measured
to ascertain and verify the relationship between
the sensor and its output. For example, when on the ground, an airplane’s
flaps may be moved at known angles, while measurements are taken on sensor
or airborne system output. The plot of angle vs. output will be used
by
the ground system for real-time data display in engineering units.
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