1. Instrumentation & Measurement
Muhajir Ab. Rahim
School of Mechatronic Engineering
Universiti Malaysia Perlis

2. Introduction
We make measurement everyday. (measure our weight, body temperature..)
The concept of measurement has been deep rooted in the human culture since the origin of civilization
In ancient times, how they measure time? length? weight?

3. Why do we need Instrumentation & Measurement?
To determine various parameters/ information of the system or a process.
To control the system variables (temperature, pressure, flow rate..) based on the collected measurement data .
Currently, automatic control systems are widely used in process industries (oil refineries, chemical plants..) and modern sophisticated systems (missile guidance, radar tracking system..)

4. What is Instrumentation?
Instrumentation is a field of study and work centering on measurement and control of physical processes.
These physical processes include pressure, temperature, flow rate, chemical consistency and etc.
An instrument is a device that measures and/or acts to control any kind of physical process.
Due to the fact that electrical quantities of voltage and current are easy to measure, manipulate, and transmit over long distances, they are widely used to represent such physical variables and transmit the information to remote locations.

5. What is Measurement?
Measurement is an act of assigning a specific value to a physical variable.
Measurand is a variable whose value is measured.
Metrology is a field of knowledge concerned with measurement.
All measurements have
1) Magnitude
2) Uncertainty
3) Units

6. Method of Measurement
All measurements involve a comparison between a measured quantity and a reference standard.
There are two fundamental methods of measurement
1) Deflection mode
2) Null mode

7. Deflection Mode
A deflection mode is a measuring method that uses signal energy to cause a deflection in the output indicator.
For example, the unknown weight of an object can be easily obtained by the deflection of a spring cause by it on the spring balance.
Spring 10 20 30
Scale

8. Null Mode
Null mode is a measuring method that balances a known amount against an unknown amount to determine the measured value
For example in equal-arm beam balance, an unknown mass when placed in the pan, causes the beam and pointer to deflect. Mass of known values are placed on the other pan till a balanced or null condition is obtained by the means of the pointer.
Equal arm 2 2
Standard mass
Unknown mass 1 1
Null position

9. Classification of Instruments
Analog and Digital Types
Self-Generating (Passive) and Power-Operated (Active) Types
Contacting and Non-Contacting Types

10. Exercise Give example of analog and digital types instrument
Give example of Passive and Active types instrument
Give example of Contacting and Non-Contacting Types instrument
Multimeter
Passive- thermometer, Bourdon tube pressure gauge Active- Accelerometer, ultrasound sensor
Non-Contacting- Pyrometer, variable reluctance tachometer Contacting- Thermometer, Bourdon tube pressure gauge

11. Generalized Measuring System
Most measuring systems fall within the framework of a general arrangement consisting of three stages:
Stage 1. A detection-transduction (sensor-transducer stage)
Stage 2. An intermediate stage (signal conditioning stage)
Stage 3. A terminating (readout- recording stage)

12. Stages of the General Measurement System
Sensor- Transducer
Stage 2:
Signal Conditioning
Stage 3:
Readout- Recording
Senses desired input to exclusion of all others and provides analogous output
Modifies transduced signal into form usable by final stage. Usually increases amplitude and/or power, depending on requirement.
Provides an indication or recording in form that can be evaluated by operator (human)
Mechanical: Contacting spindle, spring-mass, elastic devices (e.g., Bourdon tube for pressure, proving ring for force)
Electrical: Contacts, resistance, capacitance, inductance, thermocouple
Mechanical: Gearing, cranks, connecting links, cams, etc.
Electrical: Amplifying or attenuating, bridges, filters
Indicators (displacement type)
Moving pointer and scale, liquid column
Indicator (digital type): LCD display, digital printing, magnetic recording (hard disk)

13. Standard & Calibration
Standard is the known value used as the basis of calibration
Calibration is the act of applying a known input to a system to observe the system output.

14. Quality Parameters of an Instrumentation System (1/3)
Resolution: It is defined as the smallest increment in the measured value that can be detected.
Accuracy: It is a measure of difference between the measured value and actual value. Generally defined as percentage of actual value.
Precision: It is the ability of an instrument to reproduce a certain set of readings within a given deviation.
Repeatability: It is the ability to reproduce the output signal exactly when the same measured quantity is applied repeatedly under the same environmental conditions.
Range : It is defined as the limits between which inputs can vary.
Span : It is maximum value minus the minimum value of the input
Drift: It is the change in the reading of an instrument of a fixed variable with time

15. Quality Parameters of an Instrumentation System (2/3)
Sensitivity: It is the ability of the measuring instrument to respond to changes in measured quantity. It is ratio of change of output to change of input.
Sensitivity, S =∆O/∆I
I, input quantity to be sensed
O, output signal which can be recorded

16. Quality Parameters of an Instrumentation System (3/3)
Hysteresis: it is the difference in reading obtained when an instrument approaches a signal from opposite directions

17. Exercise Describe the (precision/accuracy) each of these.
Low Accuracy High Precision
High Accuracy Low Precision
High Accuracy High Precision