Transcript Electronics (2001) - University of Ottawa

Instrumentation and Signal Processing
• Signals usually need to be processed in various ways. For
example, the output signal from a transducer (sensor) may
well be contaminated with unwanted electrical “noise”.
The electrodes attached to a patient’s chest when an ECG
is taken measure the very weak electrical voltage changes
due to the activity of the heart and other muscles. The
signal is largely affected by “mains pickup” due to
electrical interference from the power supply.
• Processing the signal using a filter circuit may remove or
reduce the unwanted part of the signal. The filtering of
signals to improve signal quality or to extract important
information is done by digital techniques rather than by
analog techniques.
Riadh W. Y. Habash, SITE, 2002
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Instrumentation System
Physical Signal
Transducer
Analog Output
Analog Processing
Analog Processing
M
U
L
T
I
P
L
E
X
E
R
ADC
Computer
Display
DAC
Riadh W. Y. Habash, SITE, 2002
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Transducers
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A transducer is an electronic device that converts energy from one form to
another. Common examples include microphones, loudspeakers,
thermometers, position and pressure sensors, and antenna. No transducer is
100-percent efficient; some power is always lost in the conversion process.
Usually this loss is manifested in the form of heat.
Transducers
measure position and angle, pressure, flow rate, and
temperature, etc.
Transducers may also be divided into Analog or Digital, depending on
whether they provide a continuously varying signal (Analog) or only two
possible states (Digital)
Wheatstone bridge circuit is an example that converts a resistance change to
a voltage change. Other examples are: strain gages, potentiometers,
differential transformers, pressure transducers, fluid-flow transducers, and
temperature transducers.
For details see the textbook: pp. 281-285.
Riadh W. Y. Habash, SITE, 2002
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Bridge Circuits
[http://infoeng.ee.ic.ac.uk/~dario/courses/3e_instrumentation/1Sensors.pdf]
• The sensitivity of a sensor can be enhanced by incorporating a bridge.
Riadh W. Y. Habash, SITE, 2002
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Types of Transducers
• Passive
– Voto-voltaic
• Solar cells; portable exposure meters.
– Piezo-electric
• Gas igniters; migrophones; stress/strain guages.
– Thermo-electric
• Thermocouples.
– Electromagnetic
• Antennas! See the Figure!
Riadh W. Y. Habash, SITE, 2002
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• Active
– Variable resistor
• Thermistors; strain guages; photoconductors; diodes.
– Hall effect
• Current and field.
– Optoelectronics
• Avalanche diode;
– Variable reactance
• Variable inductance
• Variable capacitance
Riadh W. Y. Habash, SITE, 2002
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Examples of Transducers
• Microphone
• Loudspeakers
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Transducer: Sensor and Actuator
[http://www.signal.uu.se/Courses/CourseDirs/Sensors/Sensor_Intro00.PDF]
Riadh W. Y. Habash, SITE, 2002
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Types of Energy
[http://www.signal.uu.se/Courses/CourseDirs/Sensors/Sensor_Intro00.PDF]
Riadh W. Y. Habash, SITE, 2002
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Amplifiers! You know them!
[http://www.ctjc.com/tutorial.htm]
Riadh W. Y. Habash, SITE, 2002
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Filters
A filter is an electrical device which removes parts of the spectrum of a signal passed through it.
[http://www.sfu.ca/sca/Manuals/ZAAPf/i/Index_Tech.html]
• High-Pass Filter
• Low-Pass Filter
• Band-Pass Filter
• Band-Pass Reject Filter
Riadh W. Y. Habash, SITE, 2002
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