EE3403-measurements COURSE SYNOPSIS.pptx

measurements & instrumentation

1. EE3403 – Measurements and Instrumentation COURSE SYNOPSIS By Mr.J.NAGENDRAN , Assistant Professor, Department of Electrical and Electronics Engineering. Email: [email protected] 1

2. An instrument is a device in which we can determine the magnitude or value of the quantity to be measured. The measuring quantity can be voltage, current, power and energy etc. INSTRUMENTS 2

3. 3 Instruments ANALOG INSTRUMENTS DIGITAL INSTRUMENTS

4. ANALOG INSTRUMENTS The analogue instrument is defined as the instrument whose output is the continuous function of time, and they have a constant relation to the input. 4

5. CLASSIFICATION OF ANALOG INSTRUMENTS 5

6. CLASSIFICATION OF ANALOG INSTRUMENTS The indicating instruments indicates the magnitude of the measured quantity. This instrument uses the dial and pointer as an indicator. The ammeter and voltmeter belong to this category. Recording Instrument – Such type of instruments gives a continuous reading over a specified period. The variations in quantities are recorded on the sheet of papers. Recording Instrument – Such type of instruments gives a continuous reading over a specified period. The variations in quantities are recorded on the sheet of papers. 6

7. CLASSIFICATION OF ANALOG INSTRUMENTS Integrating Instruments – The instrument which measures the summation of the electrical quantity over a given period is known as the integrating instruments. Direct measuring Instruments – The instruments directly converts the measurand into energy which activates the instruments and the value of the unknown quantities measured through it. Comparison Instruments –  The comparison instruments measure the unknown quantity by comparing it with the standard value. 7

8. Principles of Operation Magnetic Effect Thermal Effect Electrostatic Effect Induction Effect Hall Effect 8

9. Principles of Operation Magnetic effect means the current flows through the conductor induces the magnetic field around it. The measurand current passes through the heating elements increases their temperature. The thermocouple attached to the element converts the temperature into an emf . The conversion of current into an emf with the help of temperature is known as the thermal effect.   9

10. Principles of Operation The electrostatic force exerted between the two charged plates. This force is used for displacing one of the plates. The instruments which work on this principle is known as the electrostatic devices. The electromotive force induces the electric current insides the drums. The interaction produced by the induced current and the emf moves the disc. This effect is mostly used in the induction effects. The material produces an electric current in the presence of a transverse magnetic field. The voltage is produced between the two edges of conductors. 10

11. TYPES OF TORQUES Deflecting torque Controlling torque Damping torque 11

12. Deflecting torque When there is no input signal to the instrument, the pointer will be at its zero position. To deflect the pointer from its zero position, a force is necessary which is known as deflecting force. A system which produces the deflecting force is known as a deflecting system. Generally a deflecting system converts an electrical signal to a mechanical force 12

13. Controlling torque To make the measurement indicated by the pointer definite (constant) a force is necessary which will be acting in the opposite direction to the deflecting force. This force is known as controlling force. Gravity control system Spring control system 13

14. In gravity controlled instruments, a small weight is attached to the moving system in such a way that it produces a controlling torque , when the moving system is in deflected position. The springs are wound in opposite direction to compensate for change of temperature. They provide necessary controlling torque and provide electrical connection to operate the coil. Under the action of deflecting torque, the In spring controlled system, controlling torque ( Tc ) is directly proportional to angle of twist (θ). Controlling torque 14

15. Damping torque Due to inertia produced by this system, the pointer oscillates about it final steady position before coming to rest. The time required to take the measurement is more.To damp out the oscillations quickly, a damping force is necessary. Air friction damping Fluid friction damping Eddy current damping 15

16. Air friction damping The piston is mechanically connected to a spindle through the connecting rod . The pointer is fixed to the spindle moves over a calibrated dial. When the pointer oscillates in clockwise direction, the piston goes inside and the cylinder gets compressed. The air pushes the piston upwards and the pointer tends to move in anticlockwise direction. If the pointer oscillates in anticlockwise direction the piston moves away and the pressure of the air inside cylinder gets reduced. The external pressure is more than that of the internal pressure. Therefore the piston moves down wards. The pointer tends to move in clock wise direction 16

17. Fluid friction damping There is similarity between fluid friction damping and air friction damping except that oil is used in place of air in case of fluid friction damping. Since viscosity of oil is greater, the damping force is also correspondingly greater. Eddy current damping Eddy currents are established in the disc since it has several closed paths. By Lenz’s law, the current carrying disc produced a force in a direction opposite to oscillating force. The damping force can be varied by varying the projection of the magnet over the circular disc. 17

18. 18