Prepared by A.R.Sivanesh AP/MECH, SRIET, Coimbatore

1. SENSORS AND
INSTRUMENTATION
UNIT I
INTRODUCTION
Prepared by
A.R.SIVANESH
Assistant Professor
Department of Mechanical Engineering
Sri Ranganathar Institute of Engineering
and Technology, Coimbatore 1

2. Measurements
 Measurement: Comparison between a
standard and what we want to measure (the
measurand).
 Two quantities are compared the result is
expressed in numerical values.
2

3. Basic requirements for a
meaningful measurement
 The standard used for comparison purposes
must be accurately defined and should be
commonly accepted.
 The apparatus used and the method adopted
must be provable (verifiable).
3

4. Two major functions of all branch
of engineering
 Design of equipment and processes
 Proper Operation and maintenance of
equipment and processes.
4

5. Methods of Measurement
 Direct Methods
 Indirect Methods
5

6. DIRECT METHODS : In these methods, the
unknown quantity (called the measurand ) is
directly compared against a standard.
INDIRECT METHOD : Measurements by direct
methods are not always possible, feasible
and practicable. In engineering applications
measurement systems are used which require
need of indirect method for measurement
purposes.
6

7. Instruments and Measurement
Systems.
instruments as a physical means
 Measurement involve the use of
of
determining quantities or variables.
 Because of modular nature of the
elements within it, it is common to refer
the measuring instrument as a
MEASUREMENT SYSTEM.
7

8. Evolution of Instruments.
a) Mechanical
b)Electrical
c) Electronic Instruments.
 MECHANICAL: These instruments are
very reliable for static and stable
conditions. But their disadvantage is that
they are unable to respond rapidly to
measurements of dynamic and transient
conditions.
8

9. Contd
 ELECTRICAL: It is faster than mechanical,
indicating the output are rapid than mechanical
methods. But it depends on the mechanical
movement of the meters. The response is 0.5 to
24 seconds.
 ELECTRONIC: It is more reliable than other
system. It uses semiconductor devices and weak
signal can also be detected.
9

10. Classification Of Instruments
 Absolute Instruments.
 Secondary Instruments.
ABSOLUTE: These instruments give the
magnitude if the quantity under
measurement terms of physical constants
of the instrument.
SECONDARY: These instruments are
calibrated by the comparison with absolute
instruments which have already been
calibrated.
10

11. Further its classified as
 Deflection Type Instruments
 Null Type Instruments.
11

12.  Functions of instrument and measuring
system can be classified into three. They
are:
i) Indicating function.
ii) Recording function.
iii) Controlling function.
 Application of measurement systems are:
i) Monitoring of process and operation.
ii) Control of processes and operation.
iii) Experimental engineering analysis.
12

13. Types Of Instrumentation
System
 Intelligent Instrumentation (data has been
refined for the purpose of presentation )
 Dumb Instrumentation (data must be
processed by the observer)
13

14. Elements of Generalized
Measurement System
 Primary sensing element.
 Variable conversion element.
 Data presentation element.
 PRIMARY SENSING ELEMENT: The
quantity under measurement makes its first
contact with the primary sensing element of
a measurement system.
 VARIABLE CONVERSION ELEMENT: It
converts the output of the primary sensing
element into suitable form to preserve the
information content of the original signal.
14

15. Contd..
 DATA PRESENTATION ELEMENT:
The information about the quantity under
measurement has to be conveyed to the
personnel handling the instrument or the
system for monitoring, control or analysis
purpose.
15

16. Functional Elements of an
Instrumentation System
PRIMARY
SENSING
ELEMENT
VARIABLE
CONVER
-SION
ELEMENT
VARIABLE
MANIPULATI-
ON ELEMENT
DATA
TRANSMISSIO
-N ELEMENT
DATACONDITIONING ELEMENT
INTERMEDIATE STAGE
DETECTOR
TRANSDUCER
STAGE
TERMINATING
STAGE
QUANTITY
TO BE
MEASURED
DATA
PRESENTA
TION
ELEMENT
16

17. SENSORS & TRANSDUCER
17

18. DEFINITION
• SENSOR
1. It is defined as an element
which produces signal
relating to the quantity
being measured
2. sensor can be defined as
“A device which provides
a usable output in response
to a specified measured.”
• TRANSDUCER
1. It is defined as an element
when subjected to some
physical
experiences a
change
related
change or an element
which converts a specified
measured into a usable
output by using a
transduction principle.
2. It can also be defined as a
device that converts a
signal from one form of
energy to another form.
18

19. TYPE OF SENSORS
AND ITS
APPLICATIONS
• IN MECHATRONICS SYSTEM
WE NEED TO MEASURE THE
FOLLOWING PHYSICAL
QUANTITIES
– SENSORS AND TRANSDUCERS
ARE THE KEY ELEMENT USED
FOR THE MEASUREMENT OF
THE PHYSICAL QUANTITIES
– DISPLACEMENT
– TEMPERATURE
– PRESSURE
– STRESS
– POSITION AND
PROXIMITY
– VELOCITY
– MOTION
– FORCE
– LIQUID FLOW
– LIQUID LEVEL
– LIGHT SENSORS
19

20. • SENSORS
– ELEMENT IN A MEASUREMENT SYSTEM THAT ACQUIRES A PHYSICAL
PARAMETER AND CHANGES INTO A SIGNAL(ALSO CAN BE DEFINED AS
PART OF A TRANSDUCER WHICH SENSES OR RESPOND TO A PHYSICAL
QUANTITY OR MEASURAND
SENSOR NORMALLY SENSES THE FOLLOWING PHYSICAL
QUANTITIES
- POSITION
- FORCES
- DISTANCE
- STRAIN
- VIBRATION
- TEMPERATURE
- ACCELERATION ETC.
EXAMPLE OF SENSOR– A THERMOCOUPLE SENSES THE CHANGE IN
TEMPERATURE
20

21. • TRANSDUCER
– CONVERTS ENERGY FROM ONE FORM TO ANOTHER
TEMPERATURE, STRAIN --------- ELECTRICAL ENERGY
EXAMPLE- ACCELEROMETER GIVES OUTPUT VOLTAGE PROPORTIONAL TO THE
MECHANICAL MOTION OF THE OBJECT
21

22. Active transducers generate electric current or voltage
directly in response to environmental stimulation (Active
transducers are those which do not require any power source for their
operation. They work on the energy conversion principle. They produce an
electrical signal proportional to the input (physical quantity). For example, a
thermocouple is an active transducer.)
Passive transducers produce a change in some passive
electrical quantity, such as capacitance, resistance, or
inductance, as a result of stimulation. These usually
require additional electrical energy for
excitation.(Transducers which require an external power source
for their operation is called as a passive transducer. They
produce an output signal in the form of some variation in
resistance, capacitance or any other electrical parameter, which
than has to be converted to an equivalent current or voltage
signal.) 22

23. EXAMPLE OF ACTIVE TRANSDUCER
23

24. EXAMPLE OF PASSIVE TRANSDUCER
24

25. Static Characteristics Of
Instruments And Measurement
Systems ( Ref 4, Chapter 2)
 Application involved measurement of
quantity that are either constant or varies
slowly with time is known as static.
Accuracy
Drift
Dead Zone
Static Error
Sensitivity
Reproducibility 25

26. Static Characteristics
Static correction
Scale range
Scale span
Noise
Dead Time
Hysteresis.
Linearity
26

27.  ACCURACY: It is the closeness with an
instrument reading approaches the true
value of the quantity being measured.
 TRUE VALUE: True value of quantity
may be defined as the average of an infinite
no. of measured value.
 SENSITIVITY is defined as the ratio of
the magnitude of the output response to that
of input response.
27

28.  STATIC ERROR: It is defined as the
difference between the measured value
and true value of the quantity.
A=Am-At
Where Am =measured value of quantity
At =true value of quantity.
It is also called as the absolute static error.
28

29.  SCALE RANGE: The scale range of an
instrument is defined as the difference
between the largest and the smallest reading
of the instrument.
Suppose highest point of calibration is Xmax
units while the lowest is Xmin units, then the
instrument range is between Xmin and Xmax.
 SCALE SPAN: Scale span or instrument
span is given as Scale span= Xmax - Xmin
It is the difference between highest and
lowest point of calibration.
29

30.  Reproducibility is specified in terms of
scale readings over a given period of time.
 Drift is an undesirable quality in industrial
instruments because it is rarely apparent
and cannot be maintained.
It is classified as
a) Zero drift
b) Span drift or sensitivity drift
c) Zonal drift.
30

31. Dynamic Characteristics of
Measurement System
( Ref 4, Chapter 4)
•Speed of response
•Measuring lag
•Fidelity
•Dynamic error
31

32. .
 SPEED OF RESPONSE :It is defined as
the rapidity with which a measurement
system responds to changes in measured
quantity. It is one of the dynamic
characteristics of a measurement system.
 FIDELITY: It is defined as the degree to
which a measurement system indicates
changes in the measured quantity without
any dynamic error.
32

33. Dynamic Error
 It is the difference between the true value
of the quantity changing with time and the
value indicated by the measurement system
if no static error is assumed. It is also
called measurement error. It is one the
dynamic characteristics.
33

34. Measuring Lag
 It is the retardation delay in the response of
a measurement system to changes in the
measured quantity. It is of 2 types:
 Retardation type: The response begins
immediately after a change in measured
quantity has occurred.
 Time delay: The response of the
measurement system begins after a dead
zone after the application of the input.
34

35. Errors in Measurement
 Limiting Errors (Guarantee Errors)
 Known Error
Classification
Gross
Error
Systematic Or
Cumulative
Error
Random Or
Residual Or
Accidental
Error
Instrumental Environmental Observational
35

36. Gross Error
 Human Mistakes in reading , recording and
calculating measurement results.
 The experimenter may grossly misread the
scale.
 E.g.: Due to oversight instead of 21.5oC,
they may read as 31.5oC
They may transpose the reading while
recording (like reading 25.8oC and
record as 28.5oC)
36

37. Systematic Errors


 INSTRUMENTAL ERROR: These errors
arise due to 3 reasons-
•Due to inherent short comings in the
instrument
•Due to misuse of the instrument
•Due to loading effects of the instrument
ENVIRONMENTAL ERROR: These errors
are due to conditions external to the measuring
device. These may be effects of temperature,
pressure, humidity, dust or of external electrostatic
or magnetic field.
OBSERVATIONAL ERROR: The error on
account of parallax is the observational error.
37

38. Residual error
This is also known as residual error. These
errors are due to a multitude of small
factors which change or fluctuate from one
measurement to another. The happenings or
disturbances about which we are unaware
are lumped together and called“Random”
or“Residual”. Hence the errors caused by
these are called random or residual errors.
38

39. Arithmetic Mean
 The most probable value of measured variable is
the arithmetic mean of the number of readings
taken.
 It is given by n
n
 x
x 
x1  x2 .....xn
Where x = arithmetic mean
 x1,x2,.. x3= readings of samples
 n= number of readings
39

40. Deviation
 Deviation is departure of the observed reading
from the arithmetic mean of the group of readings.
d1  x1  X
d2  x2  X
d3  x3  X
dn  xn  X
d1  d 2  d 3  .....  d n  0
ie
 ( x1  X )  ( x2  X )  ( x3  X )  ..  ( xn  X )
 ( x1  x2  x3  ...  xn )  n X
 n X  n X  0
40

41. Standard Deviation
 The standard deviation of an infinite number of
data is defined as the square root of the sum of the
individual deviations squared divided by the
number of readings.
d
n
d
2
d 2
1
2
d 2
1
n 1

 d 2
 d 2
 ... d 2
2 3 4
n 1
S.D  s 
 20observation
 20observation

 d 2
 d 2
 ... d 2
2 3 4
n


S.D   
41

42. Variance
n
42
2
2
2
2
 20observation
n 1
Variance  S.D  s 
 20observation
d2
d2
Variance  S.D  

43. Problem
Question: The following 10 observation were
recorded when measuring a voltage:
41.7,42.0,41.8,42.0,42.1,
41.9,42.0,41.9,42.5,41.8 volts.
1. Mean
2. Standard Deviation
3. Probable Error
4. Range.
43

44. Answer
 Mean=41.97 volt
 S.D=0.22 volt
 Probable error=0.15 volt
 Range=0.8 volt.
44

45. Calibration
 Calibration of all instruments is important since it
affords the opportunity to check the instruments
against a known standard and subsequently to find
errors and accuracy.
 Calibration Procedure involve a comparison of the
particular instrument with either
 a Primary standard
 a secondary standard with a higher accuracy than
the instrument to be calibrated.
 an instrument of known accuracy.
45

46. Standards
A standard is a physical representation of
a unit of measurement. The term ‘standard’
is applied to a piece of equipment having a
known measure of physical quantity.
46

47. Types of Standards
–International Standards (defined based
on international agreement )
–Primary Standards (maintained by
national standards laboratories)
–Secondary Standards ( used by industrial
measurement laboratories)
–Working Standards ( used in general
laboratory)
47

48. Performance measures of sensors
1.Range and Span
The range of a transducer defines the limits
between which the input can vary on the working.
The Span is the difference between the maximum
value and the minimum value.
For example, a load cell for the measurement of
forces might have a range of 0 to 50kN and its
span is 50kN (50 kN – 0 kN = 50kN).
48

49. 2.Error
Error is the difference between the result of the
measurement and the true value of the quantity
being measured.
Error = measured value – true value
For example, measurement system gives a
temperature reading of 50℃ , but the actual
reading is 49 ℃, then the error is +1℃ (50℃ –
49℃). If the actual reading is 52 ℃ , then the
error is -2℃ (50℃ – 52℃). The error can obtain
in both positive and negative values.
49

50. 3.Accuracy
It is the extent in which the value indicated by a measurement system
might be wrong. It is the summation of all the possible errors that are
likely to occur as well as the accuracy to which the transducer has
been calibrated.
For example, if the temperature of the system have a specified
accuracy of ± 5℃, this means that the reading given by the
instrument to be lie within plus or minus 5 ℃ of the true value.
Accuracy is mainly expressed in percentage of the full range.
For example, a transducer having an accuracy of ± 10% of full range
output of 0 to 500 ℃, then the reading can be expected from plus or
minus 50 ℃ of the true reading i.e., from 450 ℃ to 550℃.
50

51. 4. Sensitivity
It is normally termed as the relationship showing
how much output there is per unit input, i.e.,
output/input.
For example, a resistance thermometer has
sensitivity of 1Ω/℃. This shows that the
thermometer having sensitivity, where there is a
deflection of 1Ω for every 1℃. This is also used to
indicate the sensitivity to inputs other than being
measured.
51

52. 5. Hysteresis Error
Transducers can give different values of outputs to
the same value of quantity being measured.
So the output value will be obtained by
continuously increasing or continuously decreasing
change. This effect is called hysteresis.
The difference between the decrease in change and
increase in change on the system of measurement
known as hysteresis error.
52

53. 6. Non-Linearity error
In many Transducers linear relationship between the input and
output is assumed over the working range. i.e., for the given input
the obtained output will produce a graph of straight line.
But some times this linearity will not be occurred due to certain
possible errors. The error is defined as the maximum difference from
the straight line. It is known as Non-Linearity error. Various
methods are used for the numerical expressions of the non-linearity
error.
This error is generally defined by percentage of the full range output.
We can identify the non-linearity error by observing the linear
relationship of the input and output, plot them in a straight line on a
graph.
53

54. Then the non-linearity function for the input and
output also plot in the same graph. Surely, this non-
linearity will not be in straight line. The difference
between two graphs is called error (non-linearity
error). Below image shows the graph of non-
linearity error .
54

55. 7. Repeatability/Reproducibility
Repeatability /reproducibility in transducer is defined as the ability to
give the same output for the applications of the same input value.
ADVERTISING
The error occurring from the same output not given with repeated
applications is usually expressed as a percentage of the full range
output.
Repeatability = (max value- min value)/ full range * 100
For example, the maximum resistance measured in system of 100 ℃
is 75Ω and the minimum resistance is 0.1 Ω of the range (0 to 75
Ω), then the repeatability is calculated by
Repeatability = (75-0.1)/75 *100
Repeatability = 74.9/75 = 0.99 *100
Repeatability = 99
For the system the repeatability will be 99% for the same output
value for the same input.
55

56. 8. Stability
Stability of a transducer is the performance of a transducer which
will give the same output when used to measure the same input for a
period of time.
Normally, stability is nothing but for the constant given input the
output will be stable only for given period of time in the
measurement system.
9. Drift
The term drift is used to describe the change in output for a given
period of time for the same input.
The drift may be expressed as percentage of the full range of output.
There is a term called Zero Drift which is used to describe the
change in output on the system when there is no input or zero input.
56

57. 10. Dead Band
The dead band of a transducer is the range of input values in the system for
which there will be no output.
For example , in a Load measurement system the change of resistance will
define the amount of weight but if there will be no output for some range of
input after that output will occur similarly.
The space / time where there is no output for the input is known as Dead
Band or Dead space.
11. Resolution
When the input varies continuously over the range in the system, which may
cause small change in output signals. Resolution is nothing but small change
in input will cause the observable change in output also.
For example, in wire wound potentiometer the slider moves from one turn to
the next one which will change the output resistance reasonably. For a
transducer giving a digital output will produce a smallest change in output
signal is 1 bit.
57

58. SENSORS
58

59. Classification of sensors
Detail classification of sensors in view of their applications in manufacturing is as follows.
• A. Displacement, position and proximitysensors
• Potentiometer • Strain-gauged element • Capacitive element • Differential transformers •
Eddy current proximity sensors • Inductive proximity switch • Optical encoders • Pneumatic sensors •
Proximity switches (magnetic) • Hall effect sensors
• B. Velocity and motion
• Incremental encoder • Tachogenerator • Pyroelectric sensors
• C. Force
• Strain gauge load cell
• D. Fluid pressure
• Diaphragm pressure gauge • Capsules, bellows, pressure tubes • Piezoelectric sensors •
Tactile sensor •
• E. Liquid flow
• Orifice plate • Turbine meter F.Liquid level • Floats • Differential pressure
• G. Temperature
• Bimetallic strips • Resistance temperature detectors • Thermistors • Thermo-diodes and
transistors • Thermocouples • Light sensors • Photo diodes • Photoresistors
59

60. Sensor Calibration Techniques
60

61. Sensor Calibration in simple terms can be defined
as the comparison between the desired output
and the measured output. These errors can be
caused by various reasons. Some of the errors seen
in sensors are errors due to improper zero-
reference, errors due to shift's in sensor range, error
due to mechanical damage, etc…
Sensor Calibration Techniques
61

62. 62

63. Why do we need to calibrate sensors?
1.No sensor is perfect.
Sample to sample manufacturing variations mean that even two
sensors from the same manufacturer production run may yield
slightly different readings.
Differences in sensor design mean two different sensors may
respond differently in similar conditions. This is especially true of
‘indirect’ sensors that calculate a measurement based on one or
more actual measurements of some different, but related
parameter.
Sensors subject to heat, cold, shock, humidity etc. during
storage, shipment and/or assembly may show a change in
response.
Some sensor technologies 'age' and their response will naturally
change over time - requiring periodic re-calibration.
63

64. 2. The Sensor is only one component in the
measurement system. For example:
•With analog sensors, your ADC is part of the
measurement system and subject to variability as
well.
•Temperature measurements are subject to thermal
gradients between the sensor and the measurement
point.
•Light and color sensors can be affected by spectral
distribution, ambient light, specular reflections and
other optical phenomena.
•Inertial sensors almost always have some 'zero
offset' error and are sensitive to alignment with the
system being measured
64

65. What makes a good sensor?
The two most important characteristic of a sensor
are:
Precision - The ideal sensor will always produce
the same output for the same input.
Resolution - A good sensor will be able to reliably
detect small changes in the measured parameter.
65

66. How Do We Calibrate?
The first thing to decide is what your calibration reference will be.
Standard References
If it is important to get accurate readings in some standard units, you will need a
Standard Reference to calibrate against. This can be:
A calibrated sensor - If you have a sensor or instrument that is known to be
accurate. It can be used to make reference readings for comparison. Most
laboratories will have instruments that have been calibrated against NIST
standards. These will have documentation including the specfic reference against
which they were calibrated, as well as any correction factors that need to be applied
to the output.
A standard physical reference - Reasonably accurate physical standards can be
used as standard references for some types of sensors
Rangefinders
Rulers and Meter sticks
Temperature Sensors
Boiling Water - 100°C at sea-level
Ice-water Bath - The "Triple Point" of water is 0.01°C at sea-level
Accelerometers
Gravity is a constant 1G on the surface of the earth. 66

67. Working Principle of Sensor Calibration
• Calibration of the sensors aids in enhancing their functionality and accuracy.
Industries do sensor calibration using two well-known procedures.
• The first way involves businesses incorporating an internal calibration procedure
within their production facility to undertake customized sensor calibration.
• In this case, the business incorporates the required hardware into its design for
sensor output rectification. Through this procedure, the sensor calibration can be
adjusted to meet the needs of a particular application. However, this procedure
lengthens the time to market.
• As an alternative to this internal calibration process, several manufacturing firms
offer sensor packages that include an excellent automotive-grade MEMS sensor in
addition to full system-level calibration.
• Companies use onboard digital circuitry and software in this approach to assist
designers in enhancing the performance and usability of the sensors. Digital
circuitry, such as voltage regulation and analog signal filtering techniques, are
used to shorten the product design cycle and reduce the number of components.
• Advanced sensor fusion methods are offered to the onboard processor to enhance
overall performance and functionality. Some highly developed onboard signal
processing algorithms also aid in shortening the production process, enabling
quicker time to market. 67

68. Calibration Methods
Three different types of calibration:
One Point Calibration
Two Point Calibration
Multi-Point Curve Fitting
68

69. One Point Calibration
One point calibration is the simplest type of calibration. If your sensor
output is already scaled to useful measurement units, a one point
calibration can be used to correct for sensor offset errors in the
following cases:
Only one measurement point is needed. If you have an application
that only requires accurate measurement of a single level, there is no
need to worry about the rest of the measurement range. An example
might be a temperature control system that needs to maintain the same
temperature continuously.
The sensor is known to be linear and have the correct slope over
the desired measurement range. In this case, it is only necessary to
calibrate one point in the measurement range and adjust the offset if
necessary. Many temperature sensors are good candidates for one-
point calibration.
69

70. A one point calibration can also be used as a "drift check" to detect
changes in response and/or deterioration in sensor performance.
For example, thermocouples used at very high temperatures exhibit
an 'aging' effect. This can be detected by performing periodic one
point calibrations, and comparing the resulting offset with the
previous calibration.
70

71. How to do it:
To perform a one point calibration:
Take a measurement with your sensor.
Compare that measurement with your reference
standard.
Subtract the sensor reading from the reference
reading to get the offet.
In your code, add the offset to every sensor reading
to obtain the calibrated value.
71

72. Two Point Calibration
A Two Point Calibration is a little more complex. But it can be
applied to either raw or scaled sensor outputs. A Two Point
calibration essentially re-scales the output and is capable of
correcting both slope and offset errors. Two point calibration can be
used in cases where the sensor output is known to be reasonably
linear over the measurement range.
72

73. How to do it:
To perform a two point calibration:
Take two measurements with your sensor: One near the low end of
the measurement range and one near the high end of the
measurement range. Record these readings as "RawLow" and
"RawHigh"
Repeat these measurements with your reference instrument. Record
these readings as "ReferenceLow" and "ReferenceHigh"
Calculate "RawRange" as RawHigh – RawLow.
Calculate "ReferenceRange" as ReferenceHigh – ReferenceLow
In your code, calculate the "CorrectedValue" using the formula
below:
CorrectedValue = (((RawValue – RawLow) * ReferenceRange) /
RawRange) + ReferenceLow
73

74. Multi-Point Curve Fitting
Sensors that are not linear over the measurement range
require some curve-fitting to achieve accurate
measurements over the measurement range. A common
case requiring curve-fitting is thermocouples at
extremely hot or cold temperatures. While nearly linear
over a fairly wide range, they do deviate significantly at
extreme temperatures.
74

75. Sensor output signal types
75

76. sensor output signal types
Digital vs. Analog
First, we make a distinction between two types of outputs: an analog and a digital
output. A sensor with a digital output signals a logical value. In other words: Yes or
No, 0 or 1, True or False, Valid or Invalid . A digital output is very well-suited to
indicate the presence of an object (at a certain distance) or detecting whether a set
limit value has been reached. Does the sensor "see" the object or not? Is the value
reached or not? During a detection or non-detection the logical value changes from
a 0 to a 1, or vice versa! Examples of digital (switching) outputs are PNP/NPN,
relay, solid state relay and PushPull.
A sensor with an analog output is capable of giving a signal that is continuously
partallel to the measured value. An analog signal is a signal that can register values
without intervals. Think of a constantly fluctuating temperature in an outdoor
location, such as the conveyor belts in the production of steel beams: the analog
output changes parallel en mostly linear with the change of the measurement of the
sensor. Another example is the change of a distance from 0 to 1.000 cm or a
temperature drops from 200°C to 20°C. Examples of analog outputs are 0-10 Vdc,
4-20 mA, 0-5 Vdc or 0-20 mA. 76

77. Types of digital outputs: PNP or NPN
Sensors with a PNP or NPN switching contact
make use of a transistor output. The type of
transistor output determines whether the sensor
switches PNP or NPN. Sensors with a PNP or
NPN switching output are equipped with at least
three wires; A " + " (Pin 1 / brown wire), a " – "
(Pin 3 / blue wire) and a switching wire (Pin 4 /
black wire).
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78. PNP switching output
The load is switching between the switching
wire (4) and the – (3) within a sensor with a
PNP switching output.
78

79. NPN switching output
The load is switching between the switching
wire (4) and the + (1) within a sensor with a
NPN switching output.
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80. PushPull switching output
A PushPull output means that the switching component of a sensor
consists of two transistors. This is a type of output in which it is
possible to alternately switch PNP as well as NPN. The circuit is
designed in such a way that any voltage between a certain limit will
make the sensor switch NPN, while a lower voltage provides a PNP
output. Sensors with a PushPull output are versatile to use in
applications that require a PNP and NPN output. The advantage is
also that there is no need for developing the same sensor but with an
NPN or PNP output.
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81. Solid State Relay (SSR) output
A solid state relay (SSR) is also known as an optocoupler relay or
semiconductor relay. It is a type of relay without a mechanical
switch, contrary to a more conventional relay. Conventional
mechanical relays have the advantage of being able to switch higher
power rates, but because of moving parts are susceptible to wear and
tear. A solid state relay switches by use of a light-sensitive diode
and is, because of this, free from wear and tear. In addition it is also
capable of higher switching frequencies.
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82. Analog Outputs
The most widely used standards are current analog 4 to 20
mA and voltage of 0-10 Vdc. There are others like 1-5
VDC, 0-20 mA and 20mA -20mA.
Serial Outputs
The sensors with serial outputs are connected to networks
for field devices and the information is serially transmitted
(bit stream) through a cable network and sending data
from the sensor to the controller or supervision by a
communications port. Examples of field bus (field
networks) mentioned below: Devicenet, Profibus dp,
Foundation FieldBus and in recent years it has increased
the functionality of EtherNet/IP as a network of field.
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