Page 802 - Basic Electrical Engineering

measured into an analogous electrical signal. This signal is then amplified
and processed, and fed to a final recording device. A system comprising a
transducer, signal amplifier, converter which changes the signal from analog

to digital form, transmission system, and recording or display device is called
instrumentation system. A thermocouple, which converts an unknown

temperature into an electrical signal can be used for measurement of
temperature. The voltage induced across the thermocouple terminals

(between hot and cold junctions) can be recorded on a calibrated instrument
in terms of temperature of the hot junction.

Figure 11.1 Basic measuring system elements represented in block diagram form

Elements or components of a measuring system is shown in Fig. 11.1.
It may be noted that the common element of any measuring instrument is
the primary transducer which provides an output when input is applied to it.

A thermometer is a single measuring unit but is an example of complete
measurement system by itself. The level of mercury in the capillary tube

which rises on application of temperature to the base of the tube is used to
measure temperature directly against a graduated scale. However, most often

the transducer is only a part of the whole measurement system. The output of
the transducer often requires conversion to another form to make it suitable

for processing or conditioning. For example, a strain gauge used as
transducer causes a change in resistance when encountered with a variable
quantity. We may have to change resistance into a voltage by some method.

Such unit is called variable conversion unit as shown in Fig. 11.1.
Instruments which are used to measure various quantities that normally

change with time are called measuring instruments.
The subject instrumentation and measurement is considered most