LECTURE 1

INTRODUCTION TO INSTRUMENTATION
DR. B GASHI

Only covering instrumentation

1
 ASSESSMENT
• Inst umentation Cou sewo k 25% (5 c e its)

• Control Coursework 25% (5 credits)

• Exam 50% (10 credits)

2
 QUIZZES

WHAT ?
• in the following few slides I have put
together some short quizzes

WHY ?
• To check your prior knowledge and
understanding

3
 QUIZZ 1: What is a Sensor ?

1. A device that counts something ?

2. A machine ?
3. A software tool ?
4. Type of signal ?

4
 QUIZZ 1: What is a Sensor ?

1. A device that counts something ?

2. A machine ?
3. A software tool ?
4. Type of signal ?

Correct answer:
A device that measures a physical quantity, e.g. pressure
A sensor is a device that produces an output signal for the purpose
of sensing of a physical phenomenon, e.g. pressure, temperature, etc.
A sensor converts a physical phenomenon into a measurable analog
voltage (or sometimes a digital signal) converted into a
human-readable display or transmitted for reading or further
processing.
5
 QUIZZ 2: What is An Actuator ?

1. An Instrument ?
2. A machine ?
3. A device that converts a signal ?
4. Something else ?

6
 QUIZZ 2: What is An Actuator ?

1. An Instrument ?
2. A machine ?
3. A device that converts a signal ?
4. Something else ?
Correct answer:
A device that is responsible for moving or controlling a
mechanism or system, e.g. motor
In simple terms, an actuator is a device that makes something move or
operate by transferring a source of energy (electric, pneumatic, hydraulic) into
a physical-mechanical motion.

An example of an actuator is an electric motor.

Watch useful video
on what actuators are: https://www.youtube.com/watch?v=LHn7O6PUaoY
7
 QUIZZ 3
Place the following devices in the correct category to the right!
Relay Optical encoder CATEGORY 1 - SENSORS
Fibre optic Photo-diode

Potentiometer Thermocouple

Transistor Piezoelectric

Thermistor Hydraulic fluid

CATEGORY 2 - ACTUATORS
Strain gauge Electric motor

Pneumatic pressure Proximity

Linear variable differential transformer

Resistor Hall-effect Capacitor

8
 QUIZZ 3 - ANSWER
Place the following devices in the correct category to the right!
CATEGORY 1 - SENSORS
Photo-diode Thermocouple Optical encoder Potentiometer

Piezoelectric Thermistor Hall-effect Fibre optic

Proximity Strain gauge Linear variable differential transformer

Transistor
CATEGORY 2 - ACTUATORS
Pneumatic pressure Relay
Resistor
Hydraulic fluid Electric motor
Capacitor

9
 LECTURE PLAN
• The concept of measurement instrumentation

• Introduction to sensors (also know as transducers)

• Signal stages in measurement instrumentation

• Static performance characteristics of sensors, these include:

o Accuracy and Error

o Precision
o Range
o Sensitivity Are you familiar with
o Linearity any of these terms ?
o Hysteresis
o Drift
o Resolution Need to understand these terms

10
 WHAT IS AN INSTRUMENT ?
• A measuring Instrument is a device used for measuring, indicating, and
recording physical quantities: (1) pressure, (2) temperature, (3) strain
etc.
Recall that a sensor is a device
• Even a simple sensor can be called an instrument. that measures a physical quantity
i.e., pressure.

• Note: Sensor are sometimes referred to as transducers

• In complex systems there might be many sensors measuring

simultaneously: (1) manufacturing systems, (2) transportation
systems, (3) medical systems etc. Remember this saying If you can't measure it you
can't control it as you have no information to control.
• Collective terms used in instrumentations are: (1) instrument, (2) sensor
or transducer, (3) measurement system
If you end up working in the instrumentation field, you will hear/come across these 3 terms regularly.

11
 HERE ARE SOME SENSORS (TRANSDUCERS)

LOAD CELL STRAIN GAUGE

Can you guess

what are these
devices ?

Measures pressure
(Pressure sensor/transducer) Measures strain on an object

TEMPERATURE SENSORS

12
 NOW LET'S LOOK AT THE CONCEPT OF MEASUREMENT
What do these sensors have in
common ?
• Sensor measures a quantity and
generates an electrical signal
• The electrical signal is processed
V. important
bullet points! using electrical circuits
• The signal is converted to digital
so it can be read by a computer
Some of the quantities measured in an engine are ?
• Computer program converts the
• Engine oil temperature
• Engine oil pressure signal to the quantity measured
• Crankshaft speed • The signal is recorded, displayed
• Oxygen sensor or transmitted to a receiver.
• Throttle position sensor
Any sensor that measures
• And more... the quantity of something
has to go through the
steps above.
Can you guess how
the signal can be Slide 15 illustrates
each bullet point
used in control visually.
applications ?
Answered ~ 50:00 min 13
...NOW LET'S LOOK AT THE CONCEPT OF MEASUREMENT
It is important that the quantities listed below are measured in an engine, or else you don't know what
the engine is doing or how it is operating.

Therefore, each quantity will have a specific sensor/transducer designed to measure the quantities

However, some quantities such as power cannot be measured directly as it has more than one quantity
(work & time)

And so, each quantity of power has to be measured separately, then using the equation of power, you can
find the measured value of power.

Power
Torque
Pressure
RPM
Temperature
Oil + Fuel level
 CONCEPT OF MEASUREMENT ILLUSTRATED
From sensor signal to computer
System under
investigation
• The signal is converted to digital signal
The sensor
generates
a signal:
Say, voltage Wireless
transmission

SIGNAL PROCESSING
SIGNAL ANALOGUE PROGRAM THE
TEMPERATURE CONVERTION VOLTAGE DIGITAL DEVICE TO
SENSOR + TO CONVERT VOLTAGE
SIGNAL DIGITAL BACK TO
AMPLIFICATION CONVERSION TEMPERATURE

Sensor measures
a physical quantity: • The voltage is converted
• The signal is processed using to physical quantity:
temperature Saved to PC
electronic circuits; converted temperature
and amplified

The signal is
Y= m x
displayed on
V = k*T, solve for T = V/k screen
K = is the sensitivity factor (value found in data sheet)
V = Voltage (Output) is known as its measured
T = Temp (Input) 14
 CONCEPT OF MEASUREMENT SIMPLIFIED
1. Some SENSORS generate resistance
System under
change. We have to convert it to voltage!
investigation
2. Some SENSORS generate voltage change.
We have to modify the voltage!

3 STAGES OF
MEASURMENT
PROCESS
1ST STAGE 2ND STAGE 3RD STAGE

ARE THERE ANY QUESTIONS ? 15

 3 STAGES OF MEASUREMENT PROCESS - CASE STUDY
Temperature measurement in steel blocks

SENSORS

STEEL
HOT PLATE BLOCKS

OUTPUT
INPUT
READOUT /
TEMPERATURE SIGNAL PROCESSING
DISPLAY /
SENSOR DEVICE
TRANSMIT

1ST STAGE 2ND STAGE 3RD STAGE

16
A SHORT QUIZ (1)

17
 Q.1. SIGNAL FLOW FROM SENSOR TO COMPUTER
INPUT READOUT / OUTPUT
TEMPERATURE SIGNAL PROCESSING
DISPLAY /
SENSOR DEVICE
TRANSMIT

1ST STAGE 2ND STAGE 3RD STAGE

Place the following signal flow activities in order:

Activity The order ? Answer

The signal is modified and amplified 3
The signal is recorded, displayed or transmitted to a receiver 7
The digital signal is read by a computer 5
Sensor measures a physical quantity 1
The signal is converted to physical quantity 6
Sensor generates a signal 2
The signal is converted to digital signal (ADC) 4

18
NOW LETS LOOK A BIT CLOSER TO
INSTUMENT CHARACTERISTICS
1st STAGE DEVICES

19
 CHARACTERISTICS OF INSTRUMENTS
• Broadly speaking instruments can be characterised by their static and
dynamic performance characteristics
• In other words how sensors respond to static and dynamic inputs (loads)
Dynamic performance characteristics will be covered in the control lectures

STATIC CHARACTERISTICS DYNAMIC CHARACTERISTICS

Slowly increasing or Fast changing
decreasing pressure [oscillating] pressure

PRESSURE
SENSOR PRESSURE
SENSOR

Sensor Sensor
STATIC RESPONSE DYNAMIC RESPONSE
20
 STATIC AND DYNAMIC CHARACTERISTICS OF INSTRUMENTS

Static Characteristics Dynamic Characteristics

Precision Response time
Accuracy & Error Measuring delay
Range Fidelity
Sensitivity Dynamic error
Linearity
Hysteresis
Drift
Resolution

ARE THERE ANY QUESTIONS ?

21
 Static
STATIC CHARACTERISTICS Characteristics

Precision Precision
Accuracy
• Precision of an instrument is how close the repeated measurements are to each
Error
other
• High precision measurement instrument will give only a small spread of readings if Range

repeated readings are taken of the same quantity. Sensitivity

• Low precision measurement instrument will give a large spread of readings if Linearity
repeated readings are taken of the same quantity. Hysteresis
Drift
Example - consider the following two sets of readings obtained for Resolution
repeated measurements of the same quantity by two different
instruments: A & B

A
B
Q: Which one has higher precision ?
Instrument A has higher precision
Example - a pressure sensor might be quoted as having a repeatability
(precision) of ±0.1% of FSO. Full scale output = FSO
Thus with a full range of 20 kPa this would be an error of ±20 Pa.
22
 Full scale output (FSO) & Full scale deflection (FSD)

Full Scale Output (FSO) is the resulting output signal or displayed reading produced when the
maximum measurement for a given device is applied.

In the above example, the FSO of the pressure sensor is 20 KPa, i.e., the full range the pressure
sensor can measure is 20 KPa.

Full scale deflection refers to the full range of motion of an analog 'needle' of an analog meter,
or a galvanometer.

In the meter shown below, the amount that the needle moves away from 0 is called
the deflection.

In the example in slide 25, the FSD of the thermometer is

said to be 100 degrees celsius.
 Static
STATIC CHARACTERISTICS Characteristics

Accuracy and Error Precision

Accuracy (These two are closely related) Accuracy

• Accuracy of an instrument is how close the measured values are to the true Error
value (We never know the exact true value as there is some error in the measurements) Range
• Accuracy is often expressed as a percentage of full-scale of measurement Sensitivity
• We reefer to the full-scale of measurement as a full-scale-deflection (FSD) or
Linearity
full-scale output (FSO)
Hysteresis
Drift
Example - a thermometer might have an accuracy of ±1% of FSD.
Resolution
If the FSD is say 100°C then the accuracy is ±1°C

• The accuracy is the summation of all possible errors that are likely to occur
as well as the accuracy to which the system has been calibrated.

Error
• The term is used for the difference between the result of the measurement
and the true value of the quantity being measured. i.e.

Error = measured value – true value

Example - if the measured value is 99.9 when the true value is 100, the
error is +0.1. if the measured value is 100.1 the error is -0.1
23
 Static
STATIC CHARACTERISTICS Characteristics

Accuracy and Precision Precision

Accuracy

NOTE Error
Range
Accuracy is not the same as Precision ! Sensitivity
Linearity

It is possible for an instrument to be accurate but not Hysteresis

Drift
precise OR to be precise but not accurate. Resolution

24
 Static
STATIC CHARACTERISTICS Characteristics

Measurement Error Example Precision

Accuracy

Error
A temperature instrument measures to the nearest 2⁰C. Range
Sensitivity
You measure temperature as 25°C. Linearity
Hysteresis
Thus the temperature could be ± 1⁰C either side of 25°C (between 24⁰ and 26⁰) Drift
Resolution
Temperature = 25 ± 1⁰C
SO

Absolute error = 1⁰C

Percentage error = (1⁰ / 25⁰) * 100 = 4 %

Abs error can be converted to percentage error as shown above

Abs error = 1 degree

% error = 4%
25
 STATIC CHARACTERISTICS
Note on Measurement Error !
Absolute error of 1⁰C might not be much in some applications:

Examples: Errors can arise in a number of ways as

• Combustion Engines encountered in specifications of measurement
• Industrial Ovens and Furnaces instruments. These will be explained next...
• Etc.

However an absolute error of 1⁰C is considered unacceptable in some applications:

Examples:
• Precision Manufacturing Measuring
• Metrology and laboratory instruments Instrument
• Etc.

Example Case Study

• Consider a measurement conducted using an accurate instrument (CMM).
• Say the instrument is measuring a component machined at tight tolerances.
• Say the component is made of aluminium
• Say the ambient temperature changes by +1⁰C. This change in temperature
will make the aluminium expand by 23 µm.
Aluminium
• Hence the measurement will be wrong by 23 µm !
component

ARE THERE ANY QUESTIONS ? 26

 Static
STATIC CHARACTERISTICS Characteristics
Precision

Range Accuracy

• Range defines instrument’s measurement lower and upper limits Error

Range
Examples Sensitivity
Linearity
1. A temperature sensor has measurement limits between 0°C to 650°C Hysteresis
Range 650°C Drift
Resolution
2. A force transducer has a measurement limits between 0 kN to 100 kN
Range 100 kN

NOTE
Range is one of the first characteristic to be considered when selecting instruments.

Lets check this one -- measurement range of temperature sensor

https://www.omega.co.uk/temperature/z/thermocouple-RTD.html

Q : does range affect instrument A: Range Does NOT affect Instrument’s

accuracy? ACCURACY
27
If the instrument is used within its range as specified by the manufacturer guide, then the
range does not affect the instruments accuracy.

Essentially, if you use the instrument for what it's meant to measure, then the range does
not affect the instruments accuracy.

E.g., a vernier calliper can measure certain objects, but can't measure large objects
 Static
STATIC CHARACTERISTICS Characteristics
Precision
Sensitivity (OR static sensitivity) Accuracy
• Static sensitivity is defined as the ratio of the change in output to the Error
corresponding change in input under static or steady-state conditions Range
• In other words the slope of the best fitted line Sensitivity
Linearity
K : static sensitivity
Hysteresis
Δu : the change in input
Drift
Δy : the corresponding change in output
Resolution
(1)
More sensitive

(2)

Less sensitive

Linear static sensitivity Non- Linear static sensitivity

Q : does sensitivity affect instrument A: Sensitivity Does NOT affect
accuracy? Instrument’s ACCURACY
28
For linear sensitivity, you firstly draw the LOBF/trend line
Then, to obtain the static sensitivity, you simply find the slope/gradient of the trend line
There are instances where you sacrifice range for sensitivity because if the instrument can't measure
the full range, then what is the point of having it. Hence range is the 1st characteristic that should be
referred to first.
From the graph, we can see line 1 is steeper/has a higher slope
than line 2.
For the same input u1, we can see line 1 has a higher output
than line 2.

Therefore, line 1 has a higher sensitivity than line 2 (as shown

shown from the eq below)

For Non- linear static sensitivity you have to find the static sensitivity, k at a particular
point.

A:
Sensitivity does not affect the instrument's accuracy because a sensor is designed to respond to
(easier) to the quantity, it does not mean it's response is an inaccurate response.
 Static
STATIC CHARACTERISTICS Characteristics
Precision
Linearity (OR non-linearity)
Accuracy
• The maximum deviation from a linear relationship between input and
Error
output is non-linearity.
Range
• Non-linearity is expressed as percentage of full-scale deflection (FSD),
Sensitivity
also known as full-scale output (FSO).
Linearity
Example Hysteresis
±a An instrument produces an FSD of Drift
8.6 V and a = ± 0.3 V. Calculate Resolution
non-linearity ?
(FSD) or
(FSO)

Calculate linearity from:

Q : does linearity affect instrument ± a : the biggest distance from straight line
accuracy? FSD : full-scale deflection
A: Linearity affects Instrument’s
https://www.omega.co.uk/pptst/LCM204_LCM214.html
ACCURACY
29
a = the point which is furthest distance away from the trend line.
(For assessments, you will not be given a, you need to obtain it yourself)

Linearity/Non-linearity is calculated using the following eq:

Q:
A: Linearity does affect instruments accuracy because the instrument is calibarated so we expect
measurements to be close to the trend line. However, if we have a measurement is further away
from the trend line/expected measurements, then this will result in an untrue value will affect the
accuracy of the instrument.
 Static
STATIC CHARACTERISTICS Characteristics

Zero drift Precision

• If the output changes whilst the input remains constant at zero Accuracy

this is zero drift. Error

• It usually occurs due to ambient temperature changes. Range

Sensitivity
Q : does zero-drift affect
Linearity
instrument accuracy?
Drift
A: Drift affects Instrument’s
Hysteresis
ACCURACY
Resolution
Example
An instrument produces an FSD of 10 V
at 20⁰C. If the temperature changes to
80⁰C producing a deviation of d=0.15 V
the zero drift is:

SENSOR Temperature
effect

Calculate zero drift from:

30
 Static
STATIC CHARACTERISTICS Characteristics

Hysteresis Precision

• Hysteresis is the difference between the input-output relationship with Accuracy

input increasing and then decreasing. Error

• This can occur mainly due to friction of elements inside sensors Range
Sensitivity
Q : does hysteresis affect
Linearity
instrument accuracy?
Drift
A: Hysteresis affects Instrument’s
Hysteresis
ACCURACY
Resolution
Example
An instrument produces an FSD of 10 V
and h= ± 0.3 V. Calculate hysteresis?

Calculate hysteresis from:

±h : the biggest distance between lines

https://www.omega.com/pptst/LC202.html FSD : full-scale deflection
31
 Static
STATIC CHARACTERISTICS Characteristics
Precision
Resolution Accuracy
• Resolution defines the smallest possible change in output that can be Error
measured by an instrument. Range
Sensitivity
Example Linearity
• Say a temperature sensor can measure temperatures down to 0.01⁰C. Drift
• This sensor has a measurement resolution of 0.01⁰C. Hysteresis

Resolution
Resolution of some instruments:
• Some modern instruments have micro-scale (10-6) resolution
http://www.micro-epsilon.co.uk/2D_3D/optical-micrometer/micrometer/optoCONTROL_1200/

• Other instruments have nano-scale (10-9) resolution

http://www.micro-epsilon.co.uk/displacement-position-sensors/capacitive-sensor/

• There are also instruments with “infinite” resolution !

https://www.omega.com/pptst/LD400.html

Q : does resolution affect A: Resolution Does NOT affect

instrument accuracy? Instrument’s ACCURACY

ARE THERE ANY QUESTIONS ? 32

A SHORT QUIZ (2)

33
 Q2.1. STATIC CHARACTERISTICS OF INSTRUMENTS
List static characteristics in the table below:

Place them in here ? Answer

Precision
Accuracy & Error
Range
Sensitivity
Linearity
Hysteresis
Drift
Resolution

34
 Q2.2. STATIC CHARACTERISTICS OF INSTRUMENTS
Guess the correct answer on the left columns?
Resolution Defines the smallest possible change in output that can be produced and
detected by an instrument.
Hysteresis The difference between the input-output relationship with input increasing and
then decreasing.
Zero drift If the output changes whilst the input remains constant at zero.

Linearity The maximum deviation from a linear relationship between input and output.

Sensitivity Defines the ratio of the change in output to the corresponding change in input
under static or steady-state conditions.
Range Defines instrument’s measurement lower and upper limits.

Precision How close the repeated measurements are to each other.

Error The difference between the result of the measurement and the true value.

Accuracy How close the measured values are to the true value.

35
 DID YOU KNOW ?
• One of the most accurate measurement instrument is
LASER INTERFEROMETER

• For further information go to this link at RENISHAW

• http://www.renishaw.com/en/xl-80-laser-system--8268
36
 OTHER LEARNING ACTIVITIES

• Tutorial questions and solutions on Aula

• Further problems and applications on Aula

• Watch my videos on Aula

• Further reading online resources

37
 INSTRUMENTATION MODULE TEAM

STAFF
• Dr. Bekim Gashi (ab4278@coventry.ac.uk )
(Module Leader)
• Dr. Benedict Tan (ac7905@coventry.ac.uk )
• Dr. James Berriman (ac4210@coventry.ac.uk )

38
 FURTHER READING
BOOKS IN LIBRARY AND ONLINE
Bolton, W. (2004). Instrumentation
and control systems.

ONLINE ACCESS. ON THE LIBRARY

WEBSITE - LOCATE.

ONLINE SOURCES
https://www.omega.co.uk/?gclid=CJ2rpuqK7tYCFYS97Qod28wOQg
https://www.omega.com/techref/index.html

http://www.analog.com/en/products/sensors.html

http://www.ti.com/sensing-products/overview.html?intc=searchrecs

39