Page 8 - Instrumentation and Measurement

1.4 Terminology

Automation can be defined as the technology by which a process or procedure is performed
without human assistance.

The detecting element responds directly to the value of the variable.

A measuring element responds to the signal from the detecting element and gives a signal
representing the variable value. For example, pressure (variable), Bourdon tube (detecting element)
and linkage pointer, scale, that is, pressure gauge (measuring element).

The measuring unit comprises detecting element and measuring element.

Sensors are devices that can detect physical variables, such as temperature, light intensity, or
motion, and have the ability to give a measurable output that varies in relation to the amplitude of
the physical variable. The human body has sensors in the fingers that can detect surface roughness,
temperature, and force.

Transducer is a device to convert a signal (representing a physical quantity) of one form into a
corresponding signal of another form, retaining the amplitude variations of energy being converted.

For example, a microphone is a sound transducer (acoustic to electrical) and a loud speaker an
electrical transducer (electrical to acoustic).

Telemetering may be defined as signal transmission over a considerable distance.

Transmitters are devices used to amplify and format signals so that they are suitable for
transmission over long distances with zero or minimal loss of information. In telemetering systems,
the measuring unit is often called the transmitter, usually incorporating a transducer.

Measurement value a signal which may be Mechanical movement, torque, speed, electrical
impulse, pneumatic changes… etc.

Signal is used for display, recording, alarming and controlling and altering system variables to
desired value.

Set value (set point) SV: The command signal to a process system.

System variables: that may be measured Pressure, temperature, level, flow, density, viscosity,
position, velocity, accelerations, etc.

Error: deference between indicated & true value.

Calibrations: adjustment to give a required accuracy.

Converters are devices that are used to change the format of a signal without changing the energy
form, i.e., a change from a voltage to a current signal.

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