25-07-2012, 03:22 PM
Transducers
15905_Lect_4_Transducers_Intr_v07.pdf (Size: 37.41 KB / Downloads: 314)
Introduction
The study of sensors is multidisciplinary and requires a comprehensive knowledge of general
physics, solid-state physics, electronics, technology and semiconductor- manufacturing
techniques.
Energy information conversion is the objective of a sensor. The information available in one
energy form must be converted into the same or another energy form, with exactly the same
information content as the originating energy form.
Figure Functional block diagram of a measurement system.
The identification unit contains a device which reacts to the desired physical quantity and
converts it into an electrical quantity. The input transducer can be found here, normally called a
sensor. In the modifier stage the electrical energy is converted into another shape. In the
presentation unit, two possibilities arise depending on the nature of the 'system' to be served.
If a machine or process must be supplied with new information, the output transducer must
be able to provide it. In that case, often a type of actuator may be required to execute the right
action. In measurement systems to be perceived by humans, we need a type of display to which
our senses react, or can take action. So if we state that the output transducer is an actuator we are
always right, whether it activates a technical system or a living (biological) system.
CLASSIFICATION OF TRANSDUCERS
A transducer can be defined as a device capable of converting energy from one form into
another. Transducers can be found both at the input as well as at the output stage of a measuring
system.
The input transducer is called the sensor, because it senses the desired physical quantity and
converts it into another energy form.
The output transducer is called the actuator, because it converts the energy into a form to which
another independent system can react, whether it is a biological system or a technical system. So,
for a biological system the actuator can be a numerical display or a loudspeaker to which the
visual or aural senses react respectively. For a technical system the actuator could be a recorder
or a laser, producing holes in a ceramic material. The results can be interpreted by humans.
TRANSDUCERS - INTRODUCTION
The six different energy domains at the input of a measuring system.
We can distinguish six different energy domains: (1) radiant, (2) mechanical, (3) thermal, (4)
electrical, (5) magnetic and (6) chemical.
If certain information is already available in the electrical domain it can be claimed that it
requires no energy conversion, but in general there is 'shape' conversion left and this is just the
domain which belongs to the field of electronics and electrical science and engineering. A good
example of such a sensor only sensitive to electrical energy is the probe of an oscilloscope, with
which a good adaptation to the signal source is realized. In the modifier stage we meet other
examples of shape converters, for instance the A/D and D/A converters.
Figure The six different energy conversions at the output stage.
In the same way, the six different domain conversions at the output can be drawn. This is
illustrated in figure above, where compared with previous figure the only difference is the
reversed direction of the arrows.