Sensor - The Electronic Nose Artificial Olfaction Technology - page 27

Fig. 2.1 Block diagram of

sensor

form, which is exactly the same information content as the originating energy
form. Block diagram of sensor is shown in Fig. 2.1 .
The sensor or the sensing element is the first element in a measuring system and
takes information about the variable being measured and transforms it into a more
suitable form to be measured. Figure 2.2 illustrates the difference between sensor
and transducer.
Sensor is sometimes called a primary measuring element, it can be found
simply as a mercury thermometer to measure the temperature. It may be embedded
in the transducer to perform its function. That means the transducer consists of a
primary element (sensor) plus a secondary element (signal conditioning circuit)
that transforms the passive change or small voltage signal into active signal range
that can be easily used in other chains of the control loop.

Transducer ¼ Sensor þ Signal conditioning circuit

The differences between sensor and transducers are very negligible. A sensor
performs a transducing action, and the transducer must necessarily sense some
physical quantity. The difference lies in the efficiency of energy conversion. The
purpose of a sensor is to detect and measure, and its efficiency is 5 or 0.1 % which
is almost immaterial, provided the figure is known. A transducer, by contrast is
intended to convert energy, and its efficiency is important, though in some cases it
may not be high. Linearity of response, defined by plotting the output against the
input, is likely to be important for a sensor, but it is of much less significance for a
transducer. Example: Fig. 2.3 , Transducer configuration (displacement measure-
ment using ultrasonic sensor).
The transducer uses sensor as one of its potential operation elements, whereas a
sensor has no internal separate operating elements, and just the sensing element
itself. A transducer relies on the sensor to produce the quantity or energy con-
version. It is also capable of modifying the sensors output signal.
Sensors and their related interfacing circuits are used to measure various types
of physical properties such as temperature, force, pressure, flow, position, light

Fig. 2.2 Block diagram of sensor and transducer