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EP 320Process Instrumentation and Instrumental Analysis
January April, 2015
1. Introduction Classification of instrument.
Teaching Plan: EP320(W1 to W4)
Homework exercise
Textbook Q1.6
A thermocouple having a sensitivity of 4.8 mV/oC hasbeen used for the measurement of temperature. Itsoutput is connected to a moving coil milivoltmeterwhich has sensitivity of 1o/mV.
If the length of the pointer of the instrument is 30mm, determine the overall sensitivity oftemperature-sensing system in mm/oC.
[10 Marks]
Answer: 2.51 /
Solution: Textbook Q1.6Determine the overall sensitivity of temperature-sensing system in mm/oC.
A thermocouple having a sensitivity of 4.8 mV/oC hasbeen used for the measurement of temperature.
Its output is connected to a moving coil milivoltmeterwhich has sensitivity of 1o/mV.
length of the pointer of the instrument is 30 mm,
T
Transducer element Signal conditioning element
Data presentationelement
thermocouple Transducer = ./
Moving coil = /
Mili-volt meterV L max = 30 mm
Temperature, oC Voltage angle Pointer & scale, mm
Determine the overall sensitivity of temperature-sensing system in mm/oC.
T
Transducer element Signal conditioning element
Data presentationelement
thermocouple Transducer = ./
Moving coil = /
Mili-volt meterV L max = 30 mm
Temperature, oC Voltage Angle, o Pointer & scale, mm
Thus, max = 180o
the transfer function gain for milivoltmeter is calculated as;
=
=30
180= 0.5236 /
Finally, the overall sensitivity mm/oC is;
= = 4.8 1 0.5236 = 2.51 /
Assume semi-sphere shape meter has been used:
Solution: Textbook Q1.6
Extended exercise: Textbook Q1.6
Repeat Q1.6
Determine the unknown temperature when the output of millivolt meter is 15.482 mm
T = ? oC
Temperature measurement device
sensitivity = . / L = 15.482 mm
Temperature, oC Pointer & scale, mm
=
=
=15.482
2.51= 6.168
Instrument Parameters
1. Accuracy
2. Range
3. Span
4. Precision
5. Reproducibility
6. Sensitivity
7. Offset
8. Drift
9. Hysteresis
10. Resolution
11. Repeatability
12. Linearity
Classification of instrument
Instrument can be classified according to themode of operation, energy conversion, outputsignal, and etc.
In general is it classified as:1. Deflection and Null Types
2. Manually Operated and Automatic Types
3. Analog and Digital Types
4. Self-generating and Power-Operated Types
5. Contacting and Non-Contacting Types
6. Dumb and Intelligent Types
Operational mode of instrument
Deflection and Null Types
An iterative balancing operation using some type ofcomparator to achieve balance, and a null deflectionat parity.
Deflection Type
Null Type
Balance Input(known)
Balance Input(unknown)
Deflection and Null Types
Deflection instrument:
A measuring device whose output
deflects proportional to the
magnitude of the measurand.
Manually Operated and Automatic Types
Manual Operated Type Any instrument thatrequires the service of human.
Automatic Operated Type Any instrument thatincorporated the auxiliary device to remove manualhuman service.
Automatic type is preferred because :1. Fast dynamic response
2. Lower operational cost
Manually Operated Type example
Manually Operated Type example
Manually Operated Type example
Manually Operated Type example
Manually Operated Type example
=
Manually Operated Type example
Automatic Operated Type example
auxiliary device 0+
-
Desire Input(set-point)
Manually Operated Type: Null-bridge resistance thermometer
Manually Operated Type: Null-bridge resistance thermometer
T
Transducer element
Signal conditioning element
thermocouple Transducer
Signal ConditioningV
Temperature, oC Voltage
Data presentationelement
Scale
Actual Value
Bridge Circuit
Slider
Manual Null-detection
Automatic Operated Type: Null-bridge resistance thermometer
TTransducer element
Signal conditioning element
thermocouple Transducer
Signal ConditioningV
Temperature, oC Voltage
Data presentationelement
Scale
Actual Value
Bridge Circuit
SliderAmplifierRev. Motor
Relay
+-
controller
Desire value
Automatic Operated Type: Null-bridge resistance thermometer
Analog and Digital Types
Analog instrument present the physical variable in continuous/stepless variations with respect to time.
Digital instrument provide a signal that has been sampled from continuous data.
Analog Signal
Analog and Digital Types
Analog Signal
Digital Signal
Analog and Digital Types
Self-generating and Power-Operated Types
Photovoltaic cell (self-generating type)
Energy require by self-generating instrument are met entirely from the input signal.
Contacting and Non-Contacting Types
Variable reluctant tachometer (Proximity type)
Non-contacting instrument desire input even though they are not in-close contact with the measuring medium.
Dumb and Intelligent Types
Conventional Types - input variable is measured and display, but the data is processed by the observer.
Intelligent Type incorporated AI to process data by using microprocessor. The purpose are as follows:
1. Noise reduction
2. Auto calibration
3. Drift correction
4. Gain adjustment, etc.
Computer Based Measurement
To be continuedInstrument characteristic (Static & Dynamic)