A CLIL lesson for a Technical school

1. TRANSDUCERS
What’s the purpose of this presentation?
• To learn a technical subject ( the content) in English
(the language)
• Because there is no other way to learn a language
than listening and talking
• Because 90% of technical literature is in English
• Because we’d like you to be competitive with
European students of your age
Some friendly reminders
• From now till the end of this presentation we will
talk (possibly) in English only!
• I will speak in plain English and slowly but I won’t
speak, preferably, in Italian/English and neither in
English/Italian!
• Questions are most welcome … if they are simple!
What is a transducer ?
(a fairly good definition)
A transducer is a device which transforms a non-
electrical physical quantity (i.e. temperature, sound or
light) into an electrical signal (i.e. voltage, current,
capacity…)
Where are they used and
what for?
• Antenna: is the most basic transducer and can be made
from a simple piece of wire. It converts electromagnetic
energy into electricity when it receives signals and does the
opposite when it transmits

2. • Strain gauges: have a long thin wire attached to a foil
backing which is glued to an object. When the object
changes shape, the strain gauge also changes shape and
its resistance changes. The amount of stress or strain in the
object is calculated from this change in resistance
• Accelerometer: which converts the change in position of
mass into an electrical signal. Accelerometers measure the
force of acceleration and deceleration. They are used in car
airbags, stability control, hard drives, and many electronic
gadgets.
…more
• Geiger counter: detects radiation levels by using a
transducer called a Geiger-Muller tube
• Microphone and Speaker. Microphones convert sound
pressure waves into electrical current, while speaker convert
electrical current into sound pressure waves.
• And many many others.

3. non-electrical physical quantity
electrical signal
What is its structure
A transducer is made of three blocks:
o Input I/F
o Sensor
o Output I/F
• Another definition (American National Standards
Institute)
– A device which provides a usable output in response to a
specified measurand

4. • A sensor acquires a physical quantity and
converts it into a signal suitable for processing
(e.g. optical, electrical, mechanical)
• Nowadays common sensors convert
measurement of physical phenomena into an
electrical signal
• Active element of a sensor is called a transducer
What does Transducer
mean?
A device which converts one form of energy to
another
When input is a physical quantity and output
electrical → Sensor
When input is electrical and output a physical
quantity → Actuator

5. e.g. Piezoelectric: Force -> voltage Voltage->
Force
=> Ultrasound! Microphone, Loud Speaker
Where does it fit in the DAQ (Data
AcQuisition)
Important parameters of a
transducer
• Static response: how does it respond
to slowly variable signals, is it precise
and accurate

6. • Dynamic response: how does it
respond to quickly variable signals
(bandwidth of control system, tr, ts !!!)
• Environmental factors: how these
factors are affecting transducer
performance
• Reliability: MTBF (MTBF. Mean time between failures is
calculated in hours and is a prediction of a power supply’s reliability. MTBF = 1/λ,
failure rate. MTTF, mean time to failure, may be substituted in some datasheets for
units that will not be repaired. These definitions are purely statistical parameters and
are used to represent the reliability of (electronic) components.
Commonly Detectable Phenomena
•Biological
•Chemical
•Electric
•Electromagnetic
•Heat/Temperature
•Magnetic

7. •Mechanical motion (displacement, velocity,
acceleration, etc.)
•Optical
•Radioactivity
Common Conversion Methods
•Physical
–thermo-electric, thermo-elastic, thermo-
magnetic, thermo-optic
–photo-electric, photo-elastic, photo-magnetic,
–electro-elastic, electro-magnetic
–magneto-electric
•Chemical
–chemical transport, physical transformation,
electro-chemical
•Biological
–biological transformation, physical
transformation
Choosing a Sensor
Need for Sensors

8. • Sensors are pervasive. They are embedded
in our bodies, automobiles, airplanes, cellular
telephones, radios, chemical plants, industrial
plants and countless other applications.
• Without the use of sensors, there would be
no automation !!
– Imagine having to manually fill Poland
Spring bottles
TRANSDUCERS
• Temperature transducers
▫ Thermocouples
What is a Thermocouple
It’s a temperature sensitive device which
works
thanks to the Seebeck effect:
“a voltage is generated in a circuit
containing
two different metals by keeping the
junctions
between them at different temperatures”
Estonian physician Thomas Seebeck (1770–1831)

9. Pros and Cons in temperature
measuring using
Thermocouples
• Pros
▫ They are inexpensive.
▫ They are rugged and reliable.
▫ They can be used over a wide temperature
range.
• Cons
▫ low output voltage
▫ low sensitivity
▫ non-linearity
▫ electrical connections.

10. How does a thermocouple
look like ?
Here it is!
please note the two wires (of two different metals)
joined in the junction.
How does a thermocouple
work ?

11. High impedance voltmeter !
In normal operation, cold junction is placed in an ice bath
What types of thermocouples
can we have ?
temp. range (°C)
• Type K : Chromel - Alumel -270 / 1370
• Type J : Iron-Constantan -210 / 1050
• Type E : Chromel -Constantan -270 / 790
• Type N : Nicros -Nisil -260 / 1300
• Type T : Copper-Constantan -270 / 400
It is important to note that thermocouples measure
the temperature difference between two points, not
absolute temperature

12. More features:
• Type K ‘General Purpose' and low cost thermocouple, very
popular
• Type J Limited range (-40 to +750°C), less popular than
type K.
• Type E High output (68 mV/°C) well suited to low
temperature (cryogenic) use
• Type N High stability and resistance to high temperature
oxidation, designed as an 'improved' type K, it’s
becoming more popular.
• Type T They are used for moist or sub-zero temperature
monitoring applications because of superior corrosion
resistance
Alloys used:
• Constantan: 55% Copper and 45% Nickel
• Cromel: 90% Ni + 10% Cr
• Alumel: 95% Ni + 2% Mn + 2% Al + 1% Silicon
• Nicrosil: 14.4%Cr +1.4 Silicon + 0.1% Mn + Ni
• Nisil: same as Nicrosil but different %
How much are
thermocouples ?

13. • Type K Thermocouple (Exposed wire, fiberglass
insulated) Tip Diameter: 1.5 mm Tip Temperature: -60 to
+350 °C Price $9.90
• Type K Thermocouple (Insertion Probe) Tip Diameter:
3.3 mm Tip Temperature: -50 to +250 °C Price $39.60
Magnitude of thermal EMF
Thermal electromotive force. An electromotive force
arising from a temperature difference at two points
along a circuit, across a junction, or within an object,
as observed, for instance, in the Seebeck effect.
The temperature is usually expressed as a polynomial
function of the measured voltage. Sometimes it is
possible to get a decent linear approximation over a
limited temperature range. where
c and k = constants of the thermocouple materials
T1 = the temperature of the ‘hot’ junction
T2 = the temperature of the ‘cold’ or ‘reference’
junction
Accurate conversion of the output voltage V, to T1-T2 is
achieved either
by using calibration (lookup) tables or by using a higher
order

14. polynomial
T1 −T2= a + aV + a V 2 + + an V
Where a0, a1, ···, an are coefficients specified for each
pair of thermocouple materials, and T1-T2 is the
difference temperature in oC
Which one is the best?
Measurement circuit:
issues
We would like DVM to read only V1, but the voltmeter created two more
metallic junctions: J2 and J3 → voltmeter reading V will be proportional to the
temperature difference between J1 and J2 → we cannot find the temperature
at J1 unless we first find the temperature of J2.

16. The circuit will provide accurate readings, but it is
desirable to eliminate the ice bath
One way to do this is to replace the ice bath with
another isothermal block directly measures the
temperature of the isothermal block (the reference
junction) and use that information to compute the
unknown temperature

17. Last but not least: reference junction compensation
circuit
Thermocouple - applications
• Thermocouples are most suitable for
measuring
over a large temperature range, up to
1800 K.
• They are less suitable for applications
where smaller temperature differences
need to be measured with high
accuracy, for example the range 0–100
°C with 0.1 °C accuracy. For such

18. applications, Thermistors and RTD’s
are more suitable (Resistance -
Temperature Detectors).
Key features
• the change in electrical resistance when subjected to
a corresponding change in body temperature is
▫ Predictable
▫ Precise
▫ Stable
• extremely high temperature coefficient of resistance
• typical temperature range of -100° to over +600° F
• Thermistors are generally accepted to be the most
advantageous sensor for many applications including
temperature measurement and control.

19. Inductive transducers (IT)
• Inductive Transducers may be either
▫ Self - generating type transducers
▫ Passive type transducers.
Accelerometer–I
• Accelerometers are used to measure acceleration along
one or more axis and are relatively insensitive to orthogonal
directions
• Applications
– Motion, vibration, blast, impact, shock wave
• Mathematical description is beyond the scope of this
presentation.
Accelerometer–II
• Electromechanical device to measure acceleration forces –
Static forces like gravity pulling at an object lying at a table –
Dynamic forces caused by motion or vibration
• How they work
– Seismic mass accelerometer: a seismic mass is connected to the
object undergoing acceleration through a spring and a damper;
– Piezoelectric accelerometers: a microscopic crystal structure is
mounted on a mass undergoing acceleration; the piezo crystal is
stressed by acceleration forces thus producing a voltage

20. – Capacitive accelerometer: consists of two microstructures
(micromachined features) forming a capacitor; acceleration forces
move one of the structure causing a capacitance changes.
– Piezoresistive accelerometer: consists of a beam or
micromachined feature whose resistance changes with
acceleration
– Thermal accelerometer: tracks location of a heated mass
during acceleration by temperature sensing
Accelerometer Applications
• Automotive: monitor vehicle tilt, roll, skid, impact,
vibration, etc., to
deploy safety devices (stability control, anti-lock breaking
system,
airbags, etc.) and to ensure comfortable ride (active
suspension)
• Aerospace: inertial navigation, smart munitions,
unmanned vehicles
• Sports/Gaming: monitor athlete performance and injury,
joystick, tilt
• Personal electronics: cell phones, digital devices
• Security: motion and vibration detection
• Industrial: machinery health monitoring
• Robotics: self-balancing

21. The Accelerometer
One important mechanical transducer, already mentioned
above, is the accelerometer. It provides a measure of
acceleration in form of an electrical output signal. One
reason this sensor is of special significance is the fact that
by integrating the output signal, an accelerometer can also
provide a measure of velocity and position, figure.
Accelerometers also provide a measure for velocity and position.
Additionally to the direct digital output signal the
accelerometer should employ some sort of feedback for
closed loop operation which yields the well known
advantages over open loop devices such as an increase in
bandwidth, dynamic range and linearity. Quite often
accelerometers and other sensors are closed loop devices
having an analogue output signal which is then subjected to
an analogue to digital converter (ADC). From the systems

22. engineering point of view the entire transducer is a chain of
the closed loop sensor and an ADC, consequently many of
the advantages of having a closed loop structure are lost.
The figure illustrates this point. In this work a closed loop
accelerometer is described which incorporates the analogue
to digital conversion within the loop, to produce a true
digital transducer. However due to the complexity of this
design procedure the research programme was divided in
three stages:
. design of an open loop accelerometer,
. design of a closed loop, analogue accelerometer,
. and finally the design of an inherently digital, closed loop
accelerometer.
For the design of these devices the following key factors
could be identified:
. choice of the sensing element,
. method of signal pick-off,
. reset mechanism (for the closed loop devices),
. suitable form of compensation (for the closed loop
devices),
. system stability, static and dynamic performance.
Each stage comprises the development of a mathematical
model, simulation of the accelerometer,
implementation in hardware, measurement and testing.
The design approach used in this research work was
attempted mainly from the control engineering’s point of
view as these devices have a closed loop structure. The last
stage of the project, the design of a digital accelerometer,
was an especially challenging task because the
device is a highly nonlinear, discrete system.

23. A chain of a closed loop sensor and an ADC results in an
open loop system.
When a coil of wire is moved through a
magnetic field, a voltage is induced across the
end wires of the coil. The induced voltage is
caused by the transferring of energy from the
flux field of the magnet to the wire coil. As the
coil is forced through the magnetic field by
vibratory motion, a voltage signal representing
the vibration is produced.
The velocity probe was one of the first
vibration transducers to be built. It consists of
a coil of wire and a magnet so arranged that if
the housing is moved, the magnet tends to
remain stationary due to its inertia. The
relative motion between the magnetic field and
the coil induces a current that is proportional to
the velocity of motion. The unit thus produces
a signal directly proportional to vibration
velocity. It is self-generating and needs no
conditioning electronics in order to operate,
and it has a relatively low electrical output
impedance making it fairly insensitive to noise
induction.

24. For example, sensitivity, frequency range, residual noise
level in the measuring range, temperature range, maximum
operational and shock levels, weight, connectors,
mountings, type of out put (charge /voltages), etc.
Accelerometers are available based on applications, e.g.,
the general purpose, high sensitivity, high temperature, high
frequency (very small size), shock, human vibration, under
water, modal analysis, industrial, aerospace and flight test,
special purpose like the tri-axial and rotational
measurements, etc.
Figure

25. The seismic instrument is a device that has the functional
form of the system shown in Figure
which is a single-DOF spring-mass-damper system with the
support motion. A schematic of a typical
instrument is shown in the next Figure. The mass is
connected through the parallel spring and damper
arrangement to the housing frame. This frame is than
connected to the vibration source (e.g., bearing
housing) whose characteristics are to be measured. From
figure (spring-mass damper) using Newton’s law of motion,
we have
where 1 y and 2 y are the absolute displacements of the
housing and the suspended mass, respectively.
It is assumed that the damping force is proportional to the
velocity. We assume that a harmonic motion is applied on
the instrument such that
y1 Y1 cost
where Y is the displacement amplitude. The aim is to obtain
an expression for the relative displacement (y 1y2 in
terms of this base motion.
With mathematical passages we found the relation with the
fondamental terms natural frequency nf and critical
damping coefficient c are given by:

26. A plot of equation is given in Figure with Displacement
response of a seismic instrument as given by equation
Frequency ratio
The acceleration amplitude of the input vibration is

27. The design of a transducer for particular response
characteristics must involve a compromise between these
two effects, combined with a consideration of the
sensitivity of the displacement sensing transducer and its
transient response characteristics.
• Signal Conditioning & Analysis Equipments: The raw
signal from the vibration transducer may need to be
transformed into the right form, e.g., signals from
accelerometers may need to be integrated to provide a
velocity or displacement signal. Furthermore, signals may
need to be amplified before being fed to the metering and
alarm circuits, or in some cases passed through a filter

28. system to eliminate unwanted portions of the frequency
spectrum, and finally the system impedance may to be
reduced. All of these processes are known as signal
conditioning and this can be defined as the transformation
of the transducer signal into a form, which is suitable for
the analysis, metering, or feeding into an alarm or advance
signal processing system.
• Oscilloscope, Spectrum analyzer and Data Acquisition
System
An oscilloscope (commonly abbreviated to scope or O-
scope) is a type of electronic test equipment that allows
signal voltages to be viewed, usually as a two-dimensional
graph of one or more electrical potential differences
(vertical axis) plotted as a function of time or of some other
voltage (horizontal axis). Oscilloscope can have several
functions that helps in capturing and analysis the vibration
signal.
Depending upon the level of the signal can be amplified or
reduced. The time base can also be varied to have better
visulaising of the signal on the screen before capturing.
A spectrum analyzer is an instrument that displays signal
amplitude (strength) as it varies by signal frequency. The
frequency appears on the horizontal axis, and the amplitude
is displayed on the vertical axis. A spectrum analyzer looks
like an oscilloscope and, in fact, some instruments can
function either as oscilloscopes or/and as spectrum
analyzers. In spectrum analyzer various in-built functions
for statistical processing of periodic or random signals are
available. It includes FFT, power spectrum, autocorrelation,
cross-correlations, spectral density, probability density
function, ensemble or temporal averages, etc. Multi-channel
spectrum analyzers are very expensive and that has led to

29. the development of various software for the analysis of the
vibration signal.
Example:
Determining Natural Frequencies of the Rotor Bearing
System Using Impact Hammer Test
Natural frequencies of the rotor bearing system are
important parameters to be determined prior to any
investigation. For a two rotor system two natural
frequencies are obtained by using the impact test.
Impact is applied at one of the rigid disks while the rotor is
stationary (non-rotating). Displacement to impulse force is
measured at the bearing end both in the horizontal and
vertical directions using proximity probe transducer. The
FFT of the measured impulse response then gives
frequency domain impulse response. In the frequency
domain response natural frequencies appear as higher
amplitude peaks. Figures show the absolute value of the
FFT of the measured impulse response in the horizontal and
vertical directions, respectively. These plots indicate the
first and second natural frequencies, and these are equal to
38 Hz and 125 Hz, for the present configuration of the rotor
bearing system.

30. • Other applications are the Sound Measurements
Sound waves are a vibratory phenomenon. Acoustic effects
also give rise to “harmonic pressure fluctuations” that they
produce in a liquid or gaseous medium. They also
characterized by an energy flux per unit area and per unit
time as the acoustic waves moves through the medium. A
mathematical description of different acoustic will be given
in this section. It is standard practice in acoustic
measurements to relate the sound intensity and the sound
pressure to certain reference values 0 I0 and p0 , which
correspond to the intensity and mean pressure fluctuations
of the faintest audible sound at a frequency of 1000 Hz.

31. The magnitudes of the particle velocity and pressure
fluctuations created by a sound wave are small.
For example, a plane sound wave having an intensity of 90
dB is considered the maximum permissible level for
extended human exposure. In many circumstances we shall
be interested in the sound intensity that results from several
sound sources.