1. Electronic Instrumentation Lectrurer Touseef Yaqoob
Measurements
Basic Principle of Measurements
Electronic Instrumentation Lectrurer Touseef Yaqoob

2. Electronic Instrumentation Lectrurer Touseef Yaqoob
Learning objectives
To state sub-systems in a measurement system
To understand main function in each sub-system
To understand the basic properties of measurement systems
To understand the basic operation of ADC and DAC
Electronic Instrumentation Lectrurer Touseef Yaqoob

3. Basic components in a measurement system
It is also important to mention that a power supply is an important element for the entire system.
Electronic Instrumentation Lectrurer Touseef Yaqoob

4. Major issues in instrumentation and measurement systems
Sensitivity (deflection over the change in the variable)
Accuracy (uncertainties)
Precision (spread of readings, repeatability)
Resolution (the smallest step that can be distinguished)
Robustness (noise, disturbance, or drift)
Response time (fast response/high bandwidth)
Input impedance (loading effect)
Electronic Instrumentation Lectrurer Touseef Yaqoob

5. Electronic Instrumentation Lectrurer Touseef Yaqoob
Sensitivity
Most sensitive
Variation of the physical variables
Electronic Instrumentation Lectrurer Touseef Yaqoob

6. Electronic Instrumentation Lectrurer Touseef Yaqoob
Accuracy vs Precision
High Precision, but low accuracy.
There is a systematic error.
Electronic Instrumentation Lectrurer Touseef Yaqoob

7. Accuracy vs Precision (Cont)
High accuracy means that the mean is close to the true value, while high precision means that the standard deviation σ is small.
Electronic Instrumentation Lectrurer Touseef Yaqoob

8. Electronic Instrumentation Lectrurer Touseef Yaqoob
Response time
One would like to have a measurement system with fast response.
In other words, the effect of the measurement system on the measurement should be as small as possible.
Electronic Instrumentation Lectrurer Touseef Yaqoob

9. Finite input impedance (loading effect)
Before connection
After connection
Electronic Instrumentation Lectrurer Touseef Yaqoob

10. Electronic Instrumentation Lectrurer Touseef Yaqoob
Instruments
Converts information stored in the physical or chemical characteristics of the analyte into useful information
Require a source of energy to stimulate measurable response from analyte
Data domains
Methods of encoding information electrically
Nonelectrical domains
Electrical domains
Analog, Time, Digital
Electronic Instrumentation Lectrurer Touseef Yaqoob

11. Electronic Instrumentation Lectrurer Touseef Yaqoob
Detector
Device that indicates a change in one variable in its environment (eg., pressure, temp, particles)
Can be mechanical, electrical, or chemical
Sensor
Analytical device capable of monitoring specific chemical species continuously and reversibly
Transducer
Devices that convert information in nonelectrical domains to electrical domains and the converse
Electronic Instrumentation Lectrurer Touseef Yaqoob

12. Electronic Instrumentation Lectrurer Touseef Yaqoob
Null instruments
Electronic Instrumentation Lectrurer Touseef Yaqoob

13. Deflection instruments
Electronic Instrumentation Lectrurer Touseef Yaqoob

14. Electronic Instrumentation Lectrurer Touseef Yaqoob
Analog instruments
Electronic Instrumentation Lectrurer Touseef Yaqoob

15. Electronic Instrumentation Lectrurer Touseef Yaqoob
Digital instruments
Seven segment display
Electronic Instrumentation Lectrurer Touseef Yaqoob

16. Electronic Instrumentation Lectrurer Touseef Yaqoob
Sensing elements
The portion of a measurement system that responds directly to the physical variable being measured.
Sensing elements are usually based on some physical phenomenon of materials to the change in the environment.
Typical physical variables are:
Temperature, Level, Flow, Pressure, Force, Length, Acceleration, Velocity, Frequency, Time, …..
Electronic Instrumentation Lectrurer Touseef Yaqoob

17. Signal amplification and conditioning
Bias
The amplitude of the sensed signal is usually very small. It needs to be amplified before being processed/displayed.
Electronic Instrumentation Lectrurer Touseef Yaqoob

18. Noise reduction and filtering
Analog lowpass filter
Digital lowpass filter
Electronic Instrumentation Lectrurer Touseef Yaqoob

19. Analog to digital (ADC) & digital to analog (DAC) conversions
In many applications, one has to convert analog signals to digital forms for
further processing. This can be achieved through Analog to Digital Converter
(ADC).
In some control applications, we also need Digital to Analog Converter (DAC).
Electronic Instrumentation Lectrurer Touseef Yaqoob

20. Basic principle of Analog to Digital Converter (ADC)
Electronic Instrumentation Lectrurer Touseef Yaqoob

21. Measurements considered in this course
Temperature
Pressure
Flow
Force
Electronic Instrumentation Lectrurer Touseef Yaqoob