2. Terminology
• Transducers convert one form of energy into another
• Sensors/Actuators are input/output transducers
• Sensors can be passive (e.g. change in resistance) or active
(output is a voltage or current level)
• Sensors can be analog (e.g. thermocouples) or digital (e.g.
digital tachometer)
2
Sensor Actuator
3. Transducer types
3
Quantity
being
Measured
Input Device
(Sensor)
Output Device
(Actuator)
Light Level
Light Dependant Resistor (LDR),
Photodiode, Phototransistor, Solar Cell
Lights & Lamps, LED's &
Displays, Fiber Optics
Temperature
Thermocouple, Thermistor, Thermostat,
Resistive temperature detectors (RTD)
Heater, Fan, Peltier
Elements
Force/Pressure
Strain Gauge, Pressure Switch, Load
Cells
Lifts & Jacks,
Electromagnetic, Vibration
Position
Potentiometer, Encoders,
Reflective/Slotted Opto-switch, LVDT
Motor, Solenoid, Panel
Meters
Speed
Tacho-generator, Reflective/Slotted
Opto-coupler, Doppler Effect Sensors
AC and DC Motors,
Stepper Motor, Brake
Sound
Carbon Microphone, Piezo-electric
Crystal
Bell, Buzzer, Loudspeaker
6. Positional Sensors: Inductive Proximity Switch
6
• Detects the presence of metallic objects (non-contact) via
changing inductance
• Sensor has 4 main parts: field producing Oscillator via a
Coil; Detection Circuit which detects change in the field;
and Output Circuit generating a signal (NO or NC)
Used in traffic lights (inductive loop buried under the road). Sense
objects in dirty environment.
Does not work for non-metallic objects. Omni-directional.
7. Positional Sensors: Rotary Encoders
7
• Incremental and absolute types
• Incremental encoder needs a counter, loses absolute
position between power glitches, must be re-homed
• Absolute encoders common in CD/DVD drives
8. Temperature Sensors
8
• Bimetallic switch (electro-mechanical) – used in
thermostats. Can be “creep” or “snap” action.
• Thermistors (thermally sensitive resistors); Platinum
Resistance Thermometer (PRT), very high accuracy.
Creep-action: coil or spiral that unwinds or coils with changing
temperature
9. Thermocouples
9
• Two dissimilar metals induce voltage difference (few mV
per 10K) – electro-thermal or Seebeck effect
• Use op-amp to process/amplify the voltage
• Absolute accuracy of 1K is difficult
14. Photovoltaic Solar Cells
14
• Can convert about 20% of light power into electricity
• Voltage is low (diode drop, ~0.6V)
Solar power is 1.4kW/m^2
15. Photomultiplier tubes (PMT)
15
• Most sensitive of light sensors (can detect individual
photons)
• Acts as a current source
electrons
16. Motion sensors/transducers
16
• Switches, solenoids, relays, motors, etc.
• Motors
• DC
• Brushed/brushless
• Servo
• Stepper motors
• AC
Stepper motor
Brushed motor – permanent magnets on armature, rotor acts as electromagnet
Brushless motor – permanent magnet on the rotor, electromagnets on armature are switched
18. Piezo transducers
18
• Detect motion (high and low frequency)
• Sound (lab this week), pressure, fast motion
• Cheap, reliable but has a very limited range of motion
19. LVDT
19
LVDT is an acronym for Linear Variable Differential
Transformer. It is a common type of electromechanical
transducer that can convert the rectilinear motion of an object
to which it is coupled mechanically into a corresponding
electrical signal
20. Tachometer
20
A tachometer (revolution-counter, tach, rev-counter, RPM
gauge) is an instrument measuring the rotation speed of a
shaft or disk, as in a motor or other machine. The device
usually displays the revolutions per minute (RPM) on a
calibrated analogue dial, but digital displays are increasingly
common.
22. Capacitance transducers
22
The capacitive transducer or sensor is nothing but the
capacitor with variable capacitance. The capacitive transducer
comprises of two parallel metal plates that are separated by the
material such as air, which is called as the dielectric material.
In the typical capacitor the distance between the two plates is
fixed, but in variable capacitance transducers the distance
between the two plates is variable.
In the instruments using capacitance transducers the value of the
capacitance changes due to change in the value of the input
quantity that is to be measured. This change in capacitance can
be measured easily and it is calibrated against the input quantity,
thus the value if the input quantity can be measured directly.
24. Strain gauge
24
A Strain gauge (sometimes refered to as a Strain gage) is
a sensor whose resistance varies with applied force; It converts
force, pressure, tension, weight, etc., into a change in electrical
resistance which can then be measured. When external forces are
applied to a stationary object, stress and strainare the result.
25. ULTRASONIC
TRANSDUCERS
25
Ultrasonic transducers or ultrasonic sensors are a type of
acoustic sensor divided into three broad categories:
transmitters, receivers and transceivers. Transmitters
convert electrical signals into ultrasound, receivers convert
ultrasound into electrical signals, and transceivers can both
transmit and receive ultrasound.
26. LIGHT EMITTING DIODE
26
A light-emitting diode (LED) is a two-
lead semiconductor light source. It is a p–n
junction diode that emits light when activated.[5]When a
suitable current is applied to the leads,[6][7] electrons are
able to recombine with electron holes within the device,
releasing energy in the form of photons. This effect is
called electroluminescence, and the color of the light
(corresponding to the energy of the photon) is determined
by the energy band gap of the semiconductor. LEDs are
typically small (less than 1 mm2) and integrated optical
components may be used to shape the radiation pattern.[8]
27. LCD AND PLASMA DISPLAY
27
Plasma TVs have an edge over LCD TVs in terms of
overall picture quality but LCDs are catching up with
improvements like LED backlighting. The main
difference lies in the display technology.
Liquid Crystal Displays (LCD) panels - work by
trapping a liquid crystal solution between two sheets of
polarized glass.
28. PLASMA DISPLAY
28
Plasma displays are thinner than cathode ray tube ( CRT
)displays and brighter than liquid crystal displays ( LCD ).
...PRINCIPLE OF PLASMA DISPLAY PANELS. •
In plasma display panels the light of each picture element
is emitted from plasma created by an electric discharge.
29. SEVEN SEGMENT
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A seven-segment display (SSD), or seven-segment
indicator, is a form of electronic display device for
displaying decimalnumerals that is an alternative to the
more complex dot matrix displays.
30. DOT MATRIX DISPLAY
30
A dot-matrix display is
a display device used
to displayinformation on machines,
clocks, railway departure indicators
and many other devices requiring a
simple display device of limited
resolution.
31. GUEST HOST DISPLAY
31
Guest host displays are similar to more common liquid
crystal displays, but also include polymers, inorganic
particles, or dichroic dye within the liquid crystal matrix.
32. Summary
32
• We’ve only briefly touched on most basic types
• Many other transducers are used/common, almost for any
physical quantity one can think of
• Processing electronics is often essential: output of many
sensors is not linear, needs impedance transform, filtering,
etc.
• For additional references see
• http://www.electronics-tutorials.ws/io/io_1.html
• Handbook of Transducers by H.N. Norton
• http://www.sparkfun.com
35. CMOS
35
CMOS (complementary metal-oxide-semiconductor) is the
term usually used to describe the small amount of memory on a
computer motherboard that stores the BIOS settings. Some of
these BIOS settings include the system time and date as well as
hardware settings
37. 37
The circuit shows a half wave voltage doubler. During the negative half cycle
of the sinusoidal input waveform, diode D1 is forward biased and conducts
charging up the pump capacitor, C1 to the peak value of the input voltage,
(Vp). Because there is no return path for capacitor C1 to discharge into, it
remains fully charged acting as a storage device in series with the voltage
supply. At the same time, diode D2 conducts via D1 charging up capacitor, C2.
During the positive half cycle, diode D1 is reverse biased blocking the
discharging of C1while diode D2 is forward biased charging up capacitor C2.
But because there is a voltage across capacitor C1 already equal to the peak
input voltage, capacitor C2 charges to twice the peak voltage value of the input
signal.
In other words, V(positive peak) + V(negative peak), so on the negative half-
cycle, D1charges C1 to Vp and on the positive half-cycle D2 adds the AC peak
voltage to Vp onC1and transfers it all to C2. The voltage across
capacitor, C2 discharges through the load ready for the next half cycle.
Then the voltage across capacitor, C2 can be calculated as: Vout = 2Vp, (minus
of course the voltage drops across the diodes used) where Vp is the peak value
of the input voltage. Note that this double output voltage is not instantaneous
but increases slowly on each input cycle, eventually settling to 2Vp.
38. SINGLE CHANNEL AND
MULTICHANNEL ANALYZER
38
The multichannel
analyzer (MCA) is an important
laboratory instrument which can
measure dis- tributions of input
signals consisting of pulses. It
operates in two different modes:
pulse heightanalyzer (PHA) mode,
and multichannel scaler (MCS)
mode.
Energy form conversion: electrical signals, movement, radiant energy, thermal, or magnetic energy, etc.
Sensors/Actuators – both are transducer types
Analog-sensor-produced signals can be digitized
Can be Linear or Rotational
Used in traffic lights (inductive loop buried under the road). Sense objects in dirty environment.
Does not work for non-metallic objects. Omni-directional.
Creep-action: coil or spiral that unwinds or coils with changing temperature
Solar power is 1.4kW/m^2
Brushed motor – permanent magnets on armature, rotor acts as electromagnet
Brushless motor – permanent magnet on the rotor, electromagnets on armature are switched
