1. Electrical Measurement & Measuring Instrument
Dr. S. & S.S. Gandhy
Government Engineering College
Surat
Electrical Measurement & Measuring Instrument
Analog Measurement of
Electrical Quantities
Guided By: J.B. Patel

2. Prepared By: Enrollment No. Name 130230109013 Gajera Marvin
Golakiya Dushyant
Gosai Mayur
Goswami Drashti
Hathaliya Bharat

3. Electrostatic Type Ammeter
Progress Chart:
Electrodynamic Wattmeter
Rectifier Type Voltmeter
Three-phase Wattmeter
Electrostatic Type
Voltmeter
Electrostatic Type Ammeter
Thermo --couple

4. Topics: Thermocouple Electrostatic Type Ammeter
Electrostatic Type Voltmeter
Rectifier Type Voltmeter
Electrodynamic Wattmeter
Three-phase Wattmeter

5. 1. Thermocouple
The thermocouple is widely used temperature sensor in industry.
Whenever two different types of metals are connected together, a thermoelectric potential (sometimes called thermoelectric EMF) is generated across the two free ends the metals according to the temperature of the joint. This is known as the thermoelectric effect.
This thermoelectric effect was discovered by Thomas Johan Seeback discovered in This thermoelectric EMF is generated due to the combination of Peltier effect and Thomson effect.

6. A Typical Thermocouple
The EMF generated can be approximately expressed by the relationship:
The values of constants a1, a2, a3, etc. depend on the metals A and B
A Typical Thermocouple

7. In thermocouple temperature sensor, the temperature of hot junction is measured in respect of cold junction of vise varsa.
The thermoelectric potential is generated in a thermocouple instrument is in range of μV.
Hence, the voltmeter connected to measure the thermoelectric potential is extremely sensitive and the temperature can be read directly from this voltmeter, if it is calibrated properly in the scale of temperature.
Thermocouples are a very important class of device as they provide the most commonly used method of measuring temperatures in industry.
The major reasons behind popularity of thermocouple temperature measurement are;
They are very strong and readings are uniform,
They can measure wide range of temperatures,
Their characteristics are almost linear with a accuracy of ±0.05%.

8. Temperature Characteristics for Some Standard Thermocouple Materials

9. 2. Electrostatic Type Voltmeter
Electrostatic type instruments are almost always used as voltmeters and that too more as a laboratory rather than as industrial instruments.
The underlying principle of their operation is the force of attraction between electric charges on neighboring plates between which a p.d. is maintained.
This force gives a rise to a deflecting torque.
Unless the p.d. is sufficiently large, the force is small.
Hence, such instruments are used for measurement of very high voltages.
There are two general types of such instruments:
The quadrant type-used upto 20kV
The attracted disc type-used upto 500kV

10. 1. Quadrant Type Voltmeters
A light aluminium vane C is mounted on a spindle S and is situated partially within a hollow metal quadrant B.
When the vane and the quadrant are oppositely charged by the voltage under measurement, the vane is further attracted inwards into the quadrants thereby causing the spindle and hence the pointer to rotate.

11. 1. Attracted-Disc Type Voltmeters
It consists of two discs or plates C & D mounted parallel to each other.
Plate D is fixed and is earthed while C is suspended by a coach spring, the support for which carries a micrometer head for adjustment.
When a p.d. is applied between two plates, then C is attracted towards D but may be returned to its original position by the micrometer head.

12. 3. Rectifier Type Ammeter
To deal with current exceeding 5A, use a 5A(1A) meter in
combination with a C.T.
A.C ammeter is used with a current transformer externally
mounted, and it is noted that primary current of a current
transformer and a full scale of the meter are identical when used.
The full scale of ammeter are indicated from 5~10000A etc.
If the circuit voltage exceeds 500V even when the current is less
then 5A use a 5A (1A) meter in combination with a C.T to ensure
insulation.

13. The scale range of ammeter for motor circuit is extended up to 150%~500% of rated current, so that these meters are protected from the impact of the starting current and ensured of long life.
AM expanded scale has the normal maximum reading (upper limit of the effective measurement range) at the app. 65% point on the scale, and the rest of it (65%~100%) is devoted to extension reading (tolerance of extension area : + 5%)
Angle of deflection: 250o
ANSI C39.1, C12.10
Impulse voltage withstand 2.5KV/1min(1.2/50us)
Readily accessible span and zero adjustments

14. 4. Rectifier Type Voltmeter
The AC Volt meter is rectifier type and moving iron type.
The types of operating principle of voltmeter are the rectifier type and moving iron type.
The voltmeter is used with a potential transformer externally mounted in case of high voltage.
For higher ranges than 300V, use potential transformer (P.T) with a 150V A.C voltmeter. But the voltmeter of 600V is able to supply by order of customer.

15. When lettering the voltage ratio on voltmeter, the meters for 3-phase 4- wire are the indicating for line-to- line voltage by line-to-ground voltage, and line-to-line voltage by line-to-line voltage.
Full scale of voltmeter when use the P.T, the standard calibration value of voltmeters are 150V and/or 300V, but the full scale of voltmeters are indicated the 150V~69KV etc.
Angle of deflection: 250o
ANSI C39.1, C12.10
Impulse voltage withstand 2.5KV/1min(1.2/50us)
Readily accessible span and zero adjustments.

16. 5. Electrodynamometer Working Principle:
“When any current carrying conductor is placed inside a magnetic field, it experiences a mechanical force and due this mechanical force deflection of conductor takes place".
There are Two types of coils present in the electrodynamometer.
1. Moving Coil 2. Fixed Coil

18. Moving coil:
Moving coil moves the pointer with the help of spring control instrument. A limited amount of current flows through the moving coil so as to avoid heating.
So in order to limit the current we have connect the high value resistor in series with the moving coil. The moving is air cored and is mounted on a pivoted spindle and can moves freely.
In electrodynamometer type wattmeter, moving coil works as pressure coil.
Hence moving coil is connected across the voltage and thus the current flowing through this coil is always proportional to the voltage.

19. Fixed coil:
The fixed coil is divided into two equal parts and these are connected in series with the load, therefore the load current will flow through these coils.
Now the reason is very obvious of using two fixed coils instead of one, so that it can be constructed to carry considerable amount of electric current.
These coils are called the current coils of electrodynamometer type wattmeter.
Earlier these fixed coils are designed to carry the current of about 100 amperes but now the modern wattmeter are designed to carry current of about 20 amperes in order to save power.

20. Control system: Out of two controlling systems i.e. Gravity control
Spring control: Only spring controlled systems are used in these types of wattmeter. Gravity controlled system cannot be employed because they will appreciable amount of errors.
Damping system: Air friction damping is used, as eddy current damping will distort the weak operating magnetic field and thus it may leads to error.
Scale: There is uniform scale is used in these types of instrument as moving coil moves linearly over a range of 40 degrees to 50 degrees on either sides.

21. Advantages of Electrodynamometer Type Wattmeter:
Scale is uniform upto certain limit.
They can be used for both to measure ac as well dc quantities as scale is calibrated for both.
Errors in Electrodynamometer Type Wattmeter:
Errors in the pressure coil inductance.
Errors may be due to pressure coil capacitance.
Errors may be due to mutual inductance effects.
Errors may be due connections.(i.e. pressure coil is connected after current coil)
Error due to Eddy currents.
Errors caused by vibration of moving system.
Temperature error.
Errors due to stray magnetic field.

22. 5. Three-phase Wattmeter
A dynamometer type three- phase wattmeter consists of two separate wattmeter movements mounted together in one case with the two moving coils mounted on the same spindle.
There are two current coils and two pressure coils.
A current coil together with its pressure coil is known as an element. Therefore, a three- phase wattmeter has two elements.
The torque of each element is proportional to the power being measured by it.

23. The total deflecting torque on the moving system is proportional to the total power.
Compensation for mutual effects can be done by using Weston’s method. Resistance R may be adjusted to compensate for errors caused by mutual interference.

24. Thanks A Lot…