1. ELECTRONIC INSTRUMENTATIONS
ECE 6319
EECE 6311

2. Dr. Nor Farahidah Za’bah
Room number : E
Phone number :
address :
Website:

4. Basic Instruments
Multi-meters
Oscilloscope
Basic Architecture of Electronics Instrumentation Measurement System
Sensors and Transducers
AD and DA Conversion
Digital Signal Processing in Measurement

5. Assessment Assessments Percentage Quizzes 10% Assignment
*it can be a simulation or a lab assignment
10 %
Midterm
30%
Final Exams
50%

6. Why do we perform measurements?
To establish the validity of the design
To predict the limit of capacity
To provide information needed to supplement further work

7. INSTRUMENTS The type of instruments depends of the types of data
Steady state data
Transient data
Dynamic data
Steady state data:
If the data varies in the range of 0-5 Hz i.e value is not changing or changing very slowly
Transient data:
If the parameter variations is at much higher rate >> 5Hz.
Dynamic data:
The parameter variation is periodic

9. INSTRUMENTS
Measurement involves using an instrument is a physical means to determine the value or quantity of a variable
Different instruments are compared and analysed based on performance characteristic parameters which are divided into two:
Static Characteristic
Dynamic Characteristic

10. Static characteristic of an instrument
Instruments which are used to measure an unvarying process condition
Static performance characteristic are obtained by a process known as calibration

11. Related definitions that are associated to Static Characteristics are:
Accuracy
Precision
Sensitivity
Reproducibility
Drift
Dead Zone
Error
Static
Limiting

12. ACCURACY Closeness with which an instrument reading approaches the true value It indicates the maximum error which will not be exceeded as assured by manufacturer For example: If the accuracy of 100V voltmeter is  1%, hence the maximum error will not exceed  1V

13. PRECISION It is the measure of order to which a particular parameter is measured – simply referred to the decimal places of the a measured value For example: V is a precise value. PRECISION vs ACCURACY Precision DOES NOT necessarily guarantee accuracy. For example:  = 3.14 is a correct value or true value. This is an accurate value is a precise value AND an accurate value. However, is a precise value but it is NOT accurate

14. SENSITIVITY Indicates the capacity of the instrument to respond truly to the change in the output corresponding to the change in the input. For example: For a voltmeter, the ratio vo /  vi is referred to sensitivity REPRODUCIBILITY This is the scale reading over a period of time when the input is constantly applied. If the reading fluctuates and changes, then the reproducibility of the instrument is poor

15. DRIFT Drift is the change in output with change in the input
DRIFT Drift is the change in output with change in the input. There are three types of drift Zero Drift – the whole calibration shifts by the same amount Span Drift –the drift is not constant, but increases gradually with the deflection of the pointer Combined Drift – Both drift occurs simultaneously

16. ZERO
SPAN
COMBINED

17. DEAD ZONE The max value of input up to which the input does not respond due to hysteresis of the instrument. In other words, insensitivity of a instrument in a specific range of input signals ERROR Static Error: Defined as the difference between the true value and the measured value. If the error is constant, it is referred to as static error Limiting Error: The limit of deviation from the specified value. For example, a resistor has rated value 100  5%. The limiting error is  5%.
Example
A 600 V voltmeter is specified to be accurate within  2% at full scale. Calculate the limiting error when the instrument is used to measure voltage of 250 V
600 V   12 V deviation
(12/250) x 100% = 4.8 %

18. dynamic characteristic of an instrument
Related definitions that are associated to Static Characteristics are:
Lag
Fidelity
Speed of Response
Dynamic Error

19. LAG The speed of response of the instrument is referred to as lag
LAG The speed of response of the instrument is referred to as lag. In other words, the time delay in the output to the change in input FIDELITY Quality of indication by the instrument with regard to changes in input is known as fidelity

20. SPEED OF RESPONSE It is defined as the rapidity with which a measurement system responds to changes in measured quantity. DYNAMIC ERROR Defined as the difference between the true value and the measured value. But the error is not constant.

21. Statistical evaluation of measurement data
Arithmetic Mean (Average)
The most probable value of measured variable is the arithmetic mean of the number of readings taken.
Deviation
Deviation is departure of the observed reading from the arithmetic mean of the group of readings.
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.

22. 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. The true value is 42 V Calculate Mean, Standard Deviation, and Range.

23. Standard deviation is a number used to tell how measurements for a group are spread out from the average (mean), or expected value.
A low standard deviation means that most of the numbers are very close to the average.
A high standard deviation means that the numbers are spread out.

24. BASIC INSTRUMENTS – multi-meter
capable of measuring DC and AC voltages as well as current and resistance
contains the following elements:
Balanced-bridge DC amplifier and indicating meter
Input attenuator or RANGE switch, to limit the magnitude of the input voltage to the desired value
internal battery and additional circuitry, to provide the capability of resistance measurement
Rectifier section, to convert an AC input voltage to a proportional DC value
FUNCTION switch, to select the various measurement functions of the instrument

26. Balanced-bridge DC amplifier and indicating meter
Without input signal, the gate terminals of the FETs are at GND potential and the transistors operate under identical quiescent conditions. Ideally no current should flow through the meter
With a positive input signal applied to the gate of input transistor Q1 its drain current increases causing the voltage at the source terminal to rise. The resulting unbalance between the two transistors Q1 and Q2 source voltages is shown by the meter movement, whose scale is calibrated in terms of the magnitude of the applied input voltage.

27. Input attenuator or RANGE switch
The range of input voltages can easily be extended by an input attenuator or RANGE switch. The unknown DC input voltage is applied through a large resistor in the probe body to a resistive voltage divider. Thus, with the RANGE switch in the 3-V position as shown, the voltage at the gate of the input FET is developed across 8 M of the total resistance of 11.3 M  and the circuit is so arranged that the meter deflects full scale when 3 V is applied to the tip of the probe. With the RANGE switch in the 12-V position, the gate voltage is developed across 2 M  of the total divider resistance of 11.3 M and an input voltage of 12 V is required to cause the same full-scale meter deflection.
20 k
60 k
120 k
600 k
1.2 M
6 M
8 M

28. Resistance Measurement
Rx = the unknown resistance
When unknown resistor Rx is connected to the multi-meter, the 1.5-V battery supplies current through one of the range resistors and the unknown resistor to ground. Voltage drop Vx is then applied to the input of the bridge amplifier and causes a deflection on the meter. Since the voltage drop across Rx is directly proportional to its resistance the meter scale can be calibrated in terms of resistance.

29. Rectifier using Diodes
This combination circuit will produce the peak voltage. Initially during positive cycle, the capacitor is charged until peak value. Then, capacitor discharges through the load resistor.
The problem here is the forward voltage drop of the rectifying diodes. If we are measuring large voltages, this voltage loss may be negligible. The lowest AC voltage is normally limited to 10 V. Lower range voltages cannot be achieved because of the diode forward voltage

30. To capacitor and resistor circuitry
Rectifier using Op-amps
To capacitor and resistor circuitry

31. A multimeter when it is used as an ammeter is connected in SERIES with the measured device It will consist of a low internal impedance, but not zero A multimeter when it is used as a voltmeter is connected in PARALLEL with the measured device. It will consist of a very high internal impedance, but not infinity

32. EXAMPLE
To measure a current that circulate through a load of about 8 connected to a voltage source of 12 V, a DMM is inserted as ammeter in the 2 A range. The manufacturer specifications state that the maximum voltage drop under full scale is 700 mV.
What will be the error in the measurement due to the insertion of the ammeter?
The multi-meter is used as an AMMETER
Connected in series with the resistor
Answer: %

33. Internal resistance = 0.7 / 2 A = 0.35 
8 
12 V A
Voltage divider, V8 = (8 / 8.35)*12 = V
Error in measurement: [ – 12] / 12 * 100% = %

34. EXAMPLE
A multi-meter is used to measure a DC voltage in a circuit. The internal impedance is 10 M. What is the load effect if the Thevenin impedance is 350 k?
Answer: %

35. 350 k
V ? V
small current
Internal resistance = 10 M
Current divider, I = (10000 / 10350)* Imain
= Imain
Error in measurement: [0.966 Imain - Imain] / Imain * 100% = %

36. To extend the voltage range of a DMM up to 2000V, an external resistor is added. The DMM is used in its maximum range, which is 700V with an internal impedance of 10 M
What is the value of that resistor to get a reading of 200V when 2000V is applied?
To reduce this value to 10 M, a parallel resistor is connected to the DMM. What is the value of this resistor?
Answer: 90 M and 1.25 M