Sensors and Transducers Assignment

The provided document is a detailed solution to an assignment on sensors and transducers used in measurement. It covers various types of sensors such as thermocouples, gauge pressure sensors, tuber flow meters, capacitance level sensors, ultrasonic level sensors, and radar level sensors. The document provides a description of the operation of each sensor type, including their advantages and disadvantages. It also mentions a bibliography of references used in the research. This assignment is likely part of an instrumentation or measurement course and requires students to demonstrate their understanding of different sensing technologies.

Name of the Student
Name of the professor
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TASK 1
a) Transducer
This is a device which is involved in the conversion of energy from one state to another. It
mostly transforms a signal in one form of energy to a signal in another and usually, it is used in
the boundaries of the control system and measurements where conversion of electrical signals is
done to and from other physical quantities for example motion, light, force and energy. The
conversion of one form of energy to another is known as transduction. The transducer is selected
based on the following characteristics namely; sensitivity, drift, accuracy, precision, hysteresis,
and resolution.
Types of transducer
The mechanical and electrical transducer
Mechanical transducer is a type of transducer which converts the physical quantities into
mechanical ones while those that are involved in conversion of physical quantities into electrical
quantities are known as electrical transducer for example thermocouple which changes the
difference in temperature of small voltage or linear variable differential transformer which is
used in measuring the displacement (Reita, 2016, p. 356).
Temperature transducer
This type of transducer is an electrical device which assists in the conversion of a device
temperature into another quantity such as pressure, mechanical or electrical energy. Thereafter
the quantity will be sent to the control device for regulation of the device temperature.

Fig 1: Showing temperature transducer (Abrahams, 2017, p. 33)
The transducer is applied when measuring air temperature in a way that it controls the
temperature of numerous control system, for example, ventilation, heating, and air conditioning.
The controlling of temperature and exhibiting the measure of temperature on an LCD display is
carried out by the Arduino based automatic fan speed regulator. The fixing of temperature can be
done using the DEC and INC for increasing and decreasing.
Ultrasonic Transducer
The conversion of electrical signals to ultrasound waves is the main function of ultrasound
waves. This transducer is also known as a piezoelectric transducer and they can be used in
measuring the distance of the sound based on the reflection. In case ultrasonic transducer detect
any object or obstacle then the waves are transmitted and gets reflected back from the object then
these waves are received by the transducer

Fig 2: Showing ultrasonic transducer (Curtis, 2008, p. 54)
b) Actuator
This a part of a machine that is liable for controlling or moving a system or mechanism and they
require a source of energy and signals. It is simply a tool by which a control system acts upon the
surroundings. Its control system can be either electrical or mechanical system. The control signal
is comparatively low energy and it can be electric current or voltage, hydraulic or pneumatic or
hydraulic fluid pressure. The signals are converted into mechanical motion by the actuator after
receiving the control signals (Rayson, 2010, p. 134).
Types of actuator
Hydraulic cylinder
This is a mechanical actuator which renders a unidirectional force through a unidirectional
stroke. The power is obtained by the actuator from the pressurized hydraulic fluid which is
normally oil and it entails the barrel, piston and piston rod. The oil is pushed in the other
chamber by the piston back to the reservoir and the pressure of the oil at the end of the rod is
zero and at the head end is around zero while the pressure at the cylinder times the piston area
equals to the force on the piston (Abrahams, 2017, p. 435).

Fig 3: Showing hydraulic cylinder (Ahuja, 2008, p. 12)
Comb drive
This type of actuators is commonly used as linear actuators electrostatic forces which act
between two electrically conductive combs. Application of the voltage between the moving and
static combs leads to the creation of attractive electrostatic forces. In case the combs touch each
other then there will be no voltage difference and that is the reason why they possess that kind of
arrangement.
Fig 4: Showing a comb drive (Duncan, 2011, p. 32)
Electric motor
This is an electrical machine involves the conversion of electrical energy into mechanical energy
but the conversion of mechanical to electrical energy is done by the electric generator. An

electric motors function through contact between winding currents and magnetic field of electric
currents and most of the largest electric motors are applicable in the propulsion of ship and
pipeline compression since they are used in the production of rotary or linear torque or force
(Duncan, 2011, p. 65).
Fig 5: Showing an electric motor (Rayson, 2010, p. 76)
c) Difference between Accuracy and precision
Accuracy can be defined as the amount of uncertainty in a measurement with respect to the
absolute standard and its specifications normally comprise the effects of errors as a result from
gain and offset parameters while precision describes the measurement reducibility for example
measure of a steady state signal many times.
d) Difference between Resolution and Sensitivity
Resolution is simply the ratio between the maximum signal measured to the smaller part that can
be resolved-usually with an analog-to-digital (A/D) converter or simply the smallest
measurement that can be detected or measured by an instrument while sensitivity is an absolute
quantity, the smallest absolute amount of change that can be detected by a measurement.
e) Explain the term Hysteresis
Hysteresis is the lagging of the magnetization of a ferromagnetic material for example iron
behind variation of magnetizing field. When ferromagnetic materials are placed within a coil of

wire having an electric current, the magnetic field strength resulting from the forces of the
current or all of the atomic magnets in the materials to align with the field.
f) Explain the term Linearity
Linearity is an indicator of performance quality of a sensor. It simply tells us how the instrument
measurements correspond to the reality.
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TASK 2
Absolute pressure sensors Gauge pressure sensors Differential pressure sensors
It has a pressure range up to
360 psi
It has a pressure range of up
to 700 psi
It has a pressure range of up
to 3500 psi
Percentage accuracy of 0.5% Percentage accuracy of 1% Percentage accuracy of +/-
0.5 percent
They have pressure ranges of
600-1100 bars
The average atmospheric
pressure at sea level is
1013.25 bars
They have ranges of =1 +1
bars.
TASK 3
a) Methods of measuring temperature
The measuring of temperature can be classified into three groups which are; probes, thermometer
and non-contact
Thermometers
These are the most widely available instruments of measuring temperature and they are of
different types which include glass tube thermometer, bimetal thermometer. In case of highly
precise measurements then glass tube thermometers are preferred and since the properties of
fluids, for example, mercury is known then errors resulting to accuracy and resolution only
comes as a result of the ability of manufacturing glass tube with a precision bore. That is the

reason why some manufacturers decide to use round thermometer to increases readability and the
accuracy of these thermometers lies in the process of manufacturing and the usage.
Bimetal thermometers were made to be a minor correction but more sharp measuring device,
unlike glass thermometer. This type of thermometer is designed using metal sensing rods which
expand after sensing the temperature (Ahuja, 2008, p. 76).
Probes
The development of temperature probes came as a result of the development of the thermometer
and they were categorized under resistance elements, thermopiles, and semiconductors. The
general classification of probes has the ability to measure the temperature but they still need
extra circuity or instrumentation to make the measurement available to the user. The first probe
to exist was the resistance elements which later gave rise to the elements known as the
thermistors which change resistance with temperature. The measurement of temperature is done
by moving a minor DC current via the device and computing the voltage drop produced. Later
Resistance temperature detector (RTD) was developed in order accuracy during measurement
and this device is more accurate and linear thermocouple but the problem is that they are costlier
and respond slowly.
Non-contact devices
This category of temperature sensors entails an extensive diversity of visual devices and they
generally function on the basis of the radioactive transfer of heat measurements such that the
temperature of a device can be detected by measuring the radiation. This category consists of
single reading device and camera field device. In single reading devices, the temperature is
measured from a piece of steel emerging from the furnace and this device function by permitting
the radiation to foray an ultraviolet delicate element which is directed to this element by lenses
(Ackernan, 2007, p. 245).
b) Methods of measuring of flow
To adequately maintain the quality of industrial processes then measuring the flow rate of gases
and liquids are needed. Measuring of flow can be done by using these methods namely;
Orifice plate

This device is a low-cost device, its construction and installation are very simple. This device is
circular in shape and has a hole in the center. The dropping in pressure usually experienced when
using this device is the major limitations and the recovery of pressure can only be done partially.
The pressure in this device is needed for pumping the liquid.
Rotameter
This device works on the principle of constant area variable pressure drop and its usage is
capable in the vertical pipeline. Rotameter is simple to construct and install, also the rate of flow
can be easily be seen on the calibrated scale without the help of other devices for example
differential pressure. The rotameter consists of the vertical pipe, tapered downwards and the
passing of the flow takes place from the bottom to the top, there is a variation in the gap as a
consequence of up and down movement thus changing the orifice area. The situation of the float
is calibrated with the rate of flow (Abrahams, 2017, p. 123).
Pilot tube
The pilot tube is commonly used in measuring the aircraft velocity. Here the velocity of the fluid
at the point just before it in case a blunt object is placed in the flow channel.
c) Methods of measuring the level
The plea of innovative automated processing systems led to the need for accurate and reliable
level measurements system. The following methods are used in measuring level namely;
Glass level gauges
This the most available method for measuring the level of the liquid. It has the advantage since it
has a clear visibility which comes as a result of its design. This method has limitation since the
glass is fragile thus can cause harm to personnel.
Floats
This method involves placing a buoyant object having certain gravity between the headspace
vapor and process fluid. The float sinks at the bottom of the headspace but remains on top of the
process fluid. The main disadvantage of this method is that it cannot determine the levels
between steps which can be done by other devices.

Load cells
The calibration of load cells is done in order to make measurements ranging from fractional
ounces to tons. It is placed in the vessel support structure for level measurement and an increase
in fluid level in the vessel also leads to an increase in the force of the load cells. This method is
preferred because of their non-contact operation and the expenses during operation is minimal.
d) Methods of measuring pressure
There different types of pressure depending on their reference point, for example, atmospheric,
differential, absolute, gauge pressure. Accurately measurable pressure varies from low pressure
to extremely high pressure. The following methods are used in measuring pressure namely;
Liquid column manometers
The use of liquid column manometers entails comparing the pressure p being measured with the
height h of a liquid column. The graduated scale is read to obtain the height of the liquid and
further processing of the measurement signals is done in case higher precision is needed. The
liquids to be used in the manometer are selected based on the magnitude of the measured
pressure. The mercury, water, and alcohol are the most commonly used liquids in this type of
liquid column manometers and because of their reliability, makes them the most commonly used
method of measuring pressure. The density of the liquid used can be affected by the temperature
and also contamination of the liquid used thus causing an error when carrying out the
measurement. During reading, in case of mercury whose meniscus is convex then the reading
should be done horizontally in order to avoid parallax errors (Diesendorf, 2013, p. 45)
There are different types of manometers namely;
 U-tube manometer
 Inclined-tube manometer which is used in measuring the very low pressure of up to 4
 Multiple liquid manometers which allow magnification of different range by a factor of
8-10.
 Float type manometer which has an easy reading on a graduated scale.
Dead-weight testers

This type of measuring instrument is important in laboratories and calibration shops and they are
used as a pressure standard and in this method, the piston force is compared to the calibrated
weight force. With accuracies of 0.0005% and 0.1%, dead weight testers can be used in
measuring pressures of up to 150000PS and the sealing of the piston against the measuring
chamber is the major problem affecting this method. And also, minimum linkage should be
ensured plus error should be avoided by minimizing friction. There are some factors that need to
be considered in order to use dead weight testers as calibration equipment, they include, local
gravity, ambient air pressure, piston and cylinder deformation, mass buoyancy and temperature.
Strain foil gauges
This is the most common sensors used in measuring the pressure and they are applicable to any
deformable body using adhesive materials and this was their main advantage. There were two
types of strain foil gauges which included the metallic strain gauge and thick film strain gauge
and the most common one nowadays is the thin film strain gauges which combines all the
advantages of the conventional strain gauge such as the excellent long-term stability and low
temperature sensitivity (Curtis, 2008, p. 97).
TASK 4
The signal from the sensors is transmitted in a standard form in order to allow powering of the
device even with no process signals output from the field transmitter and to enable powering of
the remote devices with power supplied by the power controller. It is important for the signal to
be transmitted in standard form so that they can be converted from one state to another. There are
two methods used in the transmission of signals, they include;
Baseband
The signals used in baseband covers the bandwidth of the network media to transmit a single
data. This method enables transmission of multiple signals.
Broadband
This method uses analog signals in the state of electromagnetic waves or optical over multiple
transmission frequencies. It uses multiplexing approach to form multiple channels

e) A detailed description of the operation of 1 sensor
i) Thermocouple
This device is used in measuring the temperature and it contains two metals combined together
to form two junctions. The e.m.f will be generated at both junctions as a result of same, equal,
and opposite junctions and the net current flowing through the junction is zero. The e.m. f will
not become zero if they are maintained at different temperatures. And the e.m.f flowing through
the circuit depends on the metal used.
ii) Gauge pressure sensor
The mechanical gauge makes use of an internal bourdon tube where one end of the tube is
connected to the gear and shaft assembly that moves the pointer. The bourdon tube uncoils
slightly when there is an increase in pressure inside the bourdon. The gauges are connected
directly to the process fluid being measured thus as the pressure of the fluid changes, the
pressure on the bourdon tube also changes which in turn moves the pointer on the gauge.
iii) Tuber Flow Meter
This is an accurate and reliable flowmeter for both gases and liquids. In this method, as the fluid
passes through the turbine meter, its rotor rotates and the turbine rotor will rotate at high speed
directly proportional to the turbine velocity of the flowing liquid in case the friction is ignored.
The turbine meter is provided with an electrical pickup which detects the rotor rotation and then
transforms the turbine speed into pulses.
iv) Capacitance Level Sensors
Capacitance level sensor is operated by two electrodes forming a capacitor. The capacitor works
by processing the capacitance with reference to the dielectric constant. The higher levels of
dielectric material result in greater capacitance. An RF signal is activated causing a low current
to flow through the solution. The current varies depending on the amount of solution in the tank,
a difference is detected by the capacitor then translated into the output suitable for specific
applications.
f) Choose one sensor, show performance, merits and limitations
Level Sensor

i) Ultrasonic
This types of sensor are used in measuring the levels by simply calculating the strength and
duration of high-frequency sound waves that are reflected off the surface of the liquid and back
to the sensor.
Advantages
 No moving parts
 It is reliable.
 Not affected by media properties.
Disadvantages
 It is expensive.
 Its performance can be affected by various elements in the environment
ii) Radar
Radar works in a similar manner as ultrasonic but the pulses travel at the speed of light, the
reliability and repeatability can be affected by the dielectric constant. The radar can provide a
very precise level of information and also compensate for fixed structures within the containers
Advantages
 It is very accurate.
 It has multiple output options.
 No calibration is required
Disadvantages
 It is expensive.
 It can be affected by the environment.

Bibliography
Abrahams, R., 2017. Transducer and Array for underwater. s.l.: Wiley.
Ackerman, T., 2007. Piezoelectric Transducer and Applications. s.l.:Informa.
Ahuja, H., 2008. Thermal and Flow Measurements. s.l. Scholastic.
Curtis, A., 2008. Fundamentals of Temperature, Pressure and Flow Measurements. s.l.: Wiley.
Diesendorf, W., HarperCollins. Transducers for Instrumentations. s.l.:2013.
Duncan, I., 2011. Measurement in Fluid Mechanics. s.l. OLMA Media group.
Rayson, J., 2010. Instrument Technology. s.l.:Informa.
Reita, C., 2016. Instrumentation Fundamentals for Process Control. s.l. Adventure WordPress.