It is an
element which is subjec ted to physical change experience a related cha nge.
It is an
element which is not subjected to physical change experience a related change.
Range and Span:
of a transducer defines the limits between which the input can var y.
difference between the limits (maximum value - minimum value) is kno wn as
For example a load cell is us ed to measure force. An input
force can vary from 20 to 100 N. Then the range of load cell is 20 to 100 N.
And the span of load cell is 80 N (i.e., 100-
The algebraic difference betw een the indicated value and the
true value of the measured parameter is termed as the error of the device.
Indicated value — tru e value
For example, if the transduc er gives a temperature reading of
30°C when the actual temperature is 29° C, then the error is + 1°C. If the
actual temperature is
3 1° C,
then the error is — 1°C.
Accuracy is defined as the ability of the instrument to
respond to the true value of the measure variable under the reference c
For example, a thermocouple has an accuracy of ± 1° C. This
means th at reading given by the thermocouple can be expecte d to lie within +
1°C (or) — 1°C of the true valu e.
Accuracy is also expressed as a percentage of the full range
output (or) full scale deflection.
For example, a thermocouple can
be specified as having an accuracy of ±4 % of full range output. Hence if the
range of the thermocouple is 0 to 200°C, then the reading
be expected to be w ithin + 8°C (or) — 8°C of the true reading.
sensitivity is the relation ship showing how much output we can get per u nit
= Output / Input
defined as the degree of exactness for which the instrument is intended t o
When a device is used to measure any parameter plot the graph
of output Vs value of measured quantity.
First for increasing values of the measured quantity and then
for decreasing values of the measured quantity.
output readings obtained usually differ from each other.
The repeatability and reproducibility of a transducer are its
ability to give the same output for repeated applications of the same input
The reliability of a system is defined as the possibility that
it will perform its assigned functions for a specific period of time under
The stability of a transducer is its ability to give the same
output when used to measure a constant input over a period of time.
drift is the change in output that occurs over time.
There will be no output for certain range of input values.
This is known as dead band. There will be no output until the input has reached
a particular value.
It is the
time required by a transducer to begin to respond to a change in input value.
is defined as the smallest increment in the measured value that can be
The resolution is the smallest change in the input value which
will produce an observable change in the input.
Backlash is defined as the maximum distance (or) angle through
which any part of a mechanical system can be moved in one direction without
causing any motion of the attached part.
is an undesirable phenomenon and is important in the precision design of gear trains.