CLIL 5AT A.S 2014 15
Prof.ssa Busso
Transduscers
The transducer is a device that transforms one form of energy (acoustic, chemical , mechanical,
electromagnetic - including light, thermal, etc.) into another one.
For instance, as the figure below shows, the acoustical energy (pressure) of the voice is
transformed into an electronic signal and, at the end of the system, the same electronic signal is
changed again into acoustical energy.
In both cases, the device used is a transducer, but, while the first takes information from the real
world and builds a signal for an electrical equipment, the second one transforms the electrical
energy into a signal of a different type: sound, pressure, light, mechanical movement. The first type
of transducer is called sensor, the second one actuator.
We are usually able to know, by a mathematical relation, a theoretical curve, a data list, the
relationship between the physical input quantity and the output quantity .The transducer must be
very sensitive to the quantity variations we are analysing , but extremely insensitive to all the other
ones ( i.e. if you are measuring the light intensity , the measure doesn't change with the
temperature). Besides sometimes it isn’t easy to find the phenomenon or the material linking the
input and output quantity. For these characteristics the transducer is sometimes very expensive .
In everyday life transducers ( sensors) of position, velocity, acceleration, pressure, level,
temperature, light intensity, movement, electrical and electromagnetic field, humidity, frequency,
car fumes and so on are commonly used, as well as transducers (actuators) of voltage, current,
capacity, resistance, inductance, frequency....
The transducers positioned at the system input are mostly compound , not only by sensors ( a
device able to detect and transform a physical quantity in another one), but by sensor and an electric
or electronic circuit ( the conditioning circuit) to change in amplitude (to amplify or to make
smaller) and/or digitalize the signal.
Transducers can be active or passive: an active transducer builds by itself the electrical power it
needs (thermocouples, solar cells, piezoelectric sensors etc... are active transducers, while a
passive transducer needs an external power source (thermistors ,RDT, capacity and inductive
sensors are passive transducers because they always need a circuit with a voltage source).
Homework (find the name in English of the transducers you know )
Transducers can be broadly classified in two categories: discrete event and continuous. The
discrete event, or on/off sensor, changes its state according to the occurrence of some external
event. These sensors typically only detect two states based on the condition being sensed. They may
be contact type (for example, limit switches) or non-contact type (for example, proximity switches
and photoelectric sensors).
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Continuous sensors provide information over the continuous range of operation of the process and
are commonly used in continuous control applications ( for example temperature
or speed
transducers).
1.Transducer exercises 5AT
Join:
1.
2.
3.
4.
5.
6.
7.
8.
taking information to the real world
it provides information on a large value range
it needs power supply
it builds the required power supply by itself
it transforms electrical signal into other energies
it changes the amplitude of the signal
the limit switch is a
it changes the magnetic field intensity into current
a. passive
b. sensor
c. actuator
f. proximity sensor
g. on/off transducer
h. active
i. continuos transducer
l. conditionig circuit
Fill in the gaps:
1.
2.
3.
4.
5.
6.
7.
8.
9.
The piezoelectric sensor is ............ transducer
The loudspeaker changes the …........ .......into ........................
The light intensity is detected by …........ .......
The......................... builds up the electrical power.
A car fume detector transforms …......... energy into electrical one.
The …................... is able to detect the light intensity.
The motor transforms …............ energy into …........... energy.
The light bulb is …............ and transforms ......... energy into …..............energy.
The …....................... detects the value temperature and transforms it into..........................
True or false.
1.
2.
3.
4.
5.
6.
7.
Solar cells heat water directly.
The sensor transforms a physical quantity into an electrical quantity.
The thermocouples are sensors transforming the heat into voltage value.
A limit switch is a continuous transducer.
We can detect the water level with acoustic waves.
The mouse transforms rotatory movement into electrical signal.
The proximity sensor detects the changes in magnetic field ( due to the target movement)
into current variation.
8. The photoresistor detects the heating and changes its resistance .
9. In an electrical system the conditioning circuit follows the sensor.
Answer the following questions:
1.
2.
3.
4.
5.
Write the difference between sensors and actuators.
Write down the names of two transducers and explain what they do.
What is the difference between a continuous and discrete transducer? Make examples.
List the energy types you know.
What is the difference between a motor and a steam turbine generator?
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Read and fill in the gaps
Transducers are electric or electronic .................. that transform energy from one form to...........
For................, a stereo speaker converts the ...........................of recorded music into sound. Many
people think of a transducer as being a complicated, technical device designed to gather or transfer
information. In reality, however, anything that ...........energy can be considered a ............
Transducers' main characteristics .
Static characteristics.
The static characteristics of a transducer are:
 The calibration curve is a graphic (usually) relationship between the input quantity and the
output quantity :
real curve
theoretical
Fig. 2
With the calibration curve there are the
following static parameters:
1. Range of measuring quantity : is the interval x max  x min of the input signal where the
relationship is linear; above the values are compressed or clipped, below the value is too
small to be detected and there isn’t any output signal.
2. Range of the output values ( dynamic range): is the interval y max  y min of the output
signal where the relationship is linear
3. Resolution: is the smallest change of input detectable at the output. In analogue systems
the resolution is usually limited by noise. In digital systems resolution is 1 LSB (least
significant bit). A high resolution does not necessarily imply a high accuracy (a watch
may resolve to the nearest second, while it may be a few minutes off). It is very important
to realise that the resolution of an analogue device is equivalent to the resolution of a
digital device, and that no analogue circuit offers infinite resolution.
4. Sensibility : is the ratio between the output and the input variation i.e. the calibration
y  y1
y
curve slope S  2
or
x 2  x1
x
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5. Linearity error: in theory the relationship between the input and the output is a straight
line, but for the actual transducers it is not true even in the range of measuring quantity.
y  yi
We can define the linearity error
( fig.2) where yr is the actual, yi is the
  r
y fs
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9.
theoretical and y fs is the full scale value. If  is small, the transducer is roughly linear.
Zero offset : is the sensor reading ( the output) when the input is zero. It means that the
straight line is not as in fig.2, ( crossing the axis origin) , but the formula is y  mx  q .
The electronic circuit is needed to cut off the offset.
Accuracy : is the difference between the apparent value of the stimulus and the actual
value. (See resolution)
Repeatability: defines the long-term reliability .
Hysteresis : the output value for the same input is different if the measuring quantity is
increasing or decreasing.
Dynamic characteristics
The dynamical characteristics are parameters for studying the transducer behavior when the input
signal changes very fast or when the signal is complex.:
1. Frequency responses are the amplitude and phase spectra of the transducer. If the
transducer has a high threshold frequency, could follow a fast signal, but it doesn’t
cut off the noise ( the noise has mostly high frequency components) and it’s
difficult to digitalize the signal ( we are going to study this when we will learning
the A/D and D/A converter).
2. Time constant when the input signal is a
square pulse,  is the time required to reach the
69% of the final value (fig. 3). It defines the
response speed of the transducer.
There is a relation between the time costant and the cut
off frequency : f c  1 .
4  5
2.Transducer main characteristics exercises 5AT
Join:
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1.
10.
11.
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14.
15.
16.
the difference between the real and the apparent value
the detection of the smallest input
reliability during time
the calibration slope
the amplitude and phase spectra
the time required to reach the 69% of the final value
threshold frequency
the difference between the real and the theoretical value divided
by the full scale value
a. repeatibility
b. accuracy
c. resolution
d. linearity error
e. sensibility
f. frequency response
g. cut off frequency
h. time constant
Fill in the gaps:
1.
2.
3.
4.
5.
6.
7.
8.
You can say something about the response speed of a transducer if you know its …................
The dynamic range is the interval of the …................ where the relation is linear.
The …........... is the highest value of the output signal.
The amplitude and phase spectra are the …................
When the temperature rises , the voltage output rises, when it goes down the output voltage
goes down, but the value is smaller; there is.............
When the threshold ...........is high , the transducer could ........... a fast signal.
If ,when the input in zero, there is an output value, you have a........... ............
The ............. curve is the relationship between the input ............ and the output .................
True or false.
1.
2.
3.
4.
5.
6.
7.
8.
The linearity error is the ratio between the output and the input variation.
The sensibility is the ratio between the input and the output variation.
The time constant is the time in which the transducer output reaches the final value.
The time constant is the time in which the transducer input reaches the final value.
The cut off frequency is inversely proportional to the time constant.
The resolution is the smallest change in the signal output.
The cut off frequency is the highest frequency you can find into the signal.
When you have a zero offset the calibration curve formula is y  mx
Answer the following questions:
1.
2.
3.
4.
5.
6.
What is a calibration curve?
Define the dynamical parameters.
Definition of sensibility ( draw the calibration curve and the sensibility on it too).
Define the time constant.
What are the amplitude and phase spectra?
What is the linearity error?
Read and fill in the gaps
Sensors and Actuators
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There are many different types of transducers, but at their most basic, they can be divided into two
groups: input ( .............) and ..........(actuator). Input transducers take some sort of ...........energy —
such as sound waves, temperature, or pressure — and convert it into a signal that can be read.
A..................., for example, converts sound waves that strike its ..............into an electrical signal that
can be transmitted over wires. A ................. turns the physical force being exerted on it into a number
or reading that can be easily.................
Actuators take an .....................and convert it ..........physical energy. A stereo speaker works by
...................the electronic signal of a recording into physical sound waves. ..............motors are another
common form of electromechanical transducer, converting ............... into mechanical energy to
................a task.
1.
Combining Transducers
Many devices work by ......................sensors and actuators to convert energy from one form to another
and then back ............... Audio cassettes, for example, are created by using a transducer to turn the
............................from the microphone pick-up — which converted the .............waves into an electrical
signal — into ....................fluctuations on the tape head. These magnetic fluctuations are then
..........and ............by another transducer — in this case, the stereo system — to be turned back into an
electrical signal. This signal is then fed by .........to speakers, which turn the electrical signal back into
audio.............
Ultrasound imaging also ........... by converting energy many times. A piezoelectric ................ is used
to convert electricity into high frequency .....................(ultrasound), which are focused by the machine
and aimed at body tissues. These waves bounce back to the machine, where a transducer converts
........ into electrical signals again. The signals are processed and ......... to a monitor to produce an
............ of the body .............
Other everyday tasks are .............. through the use of energy that is ........... multiple times. Turning on
an electric light .............. electrical energy to be converted into visible ........... That electrical energy first
had to be generated, however; an electrical ............ is a type of transducer that turns .................(or
kinetic) energy into electricity that can then be .................other devices.
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