Classification (Analog instruments)
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The document discusses the classification and principles of various measuring instruments, including electromagnetic, electrostatic, and electrothermal types. It focuses on electromechanical indicating instruments, specifically Permanent Magnet Moving Coil (PMMC) instruments, detailing their construction, operation, and the torques involved in measurement. Additionally, it addresses issues such as temperature effects, compensation methods, and the advantages and limitations of ammeters and voltmeters.
Classification (Analog instruments)
- 1. Classification of Measuring Instruments • Quantity measured • Principle of operation •Principle of operation 1) Electromagnetic (Force due to B & I) 2) Electrostatic (Force due to E & Q) 3) Electro thermal (due to heating effect)
- 2. Electromagnetic-Electromechanical Indicating Instruments Electromechanical Indicating Instruments Input is electrical signal Output is mechanical force Analog (Output is a continuous function of time) Example: PMMC Instruments
- 3. Permanent Magnet Moving Coil (PMMC) Instruments • To measure DC current or DC voltage • Can be used for measuring AC currents and voltages by introducing additional circuit and proper calibration
- 4. Constructional Features of PMMC
- 5. Constructional Features of PMMC
- 6. 6 Various Forces/ Torques in Measuring Instruments • The movement of the pointer in PPMC is governed by three different torques 1) Deflection Torque 2) Control Torque 3) Damping Torque
- 13. 13 Two methods of supporting the moving system
- 14. 14 Two methods of supporting the moving system
- 15. 15 • Examination of torque equation • Reason for placing hair springs in opposite direction • Why taut band is used • How to use PMMC for AC • Effect of temp, Swamping resistance • Multi range ammeters and voltmeters •What switches should be used • Advantages, Limitations and sources of error • Ammeter and voltmeter sensitivity
- 16. 16 Effect of temperature and methods to compensate • Hair springs, Magnetic field, Coil resistance are effected • Series resistance with temperature coefficient nearly zero (manganin) • Usually three the coil resistance •It is called Swamping resistance
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