In this note, Poly Notes Hub discusses the Construction, Working Principles, Advantages, and Disadvantages of the PMMC instrument.
Author Name: Arun Paul.
What is PMMC ?
Permanent magnet moving coil, or PMMC, instruments are those that use a permanent magnet to create the stationary magnetic field in which the coil travels. It functions according to the principle that a moving coil positioned within a permanent magnet’s field experiences torque. When measuring DC, the PMMC device provides an accurate result.
Construction
Below we discuss about the construction of PMMC instrument or Permanent Magnet Moving Coil Instrument.
- Moving Coil: The instrument’s coil, which freely moves between the permanent magnet’s stationary field, is what carries current. The coil deflects as a result of the current flowing through it, allowing the voltage or current to be calculated. The aluminium rectangular former is where the coil is installed. The former strengthens the consistent, radial magnetic field that exists between the poles’ air gaps. The silk cover copper wire is twisted around a magnet’s poles to create a coil.
- Magnet System: The permanent magnet that the PMMC instrument uses to create the stationary magnets is made of Alcomax and Alnico material because of its high coercive force, which modifies the magnetization property of the material, and its high field intensities.
- Control: The springs in the PMMC instrument are that control the torque. The phosphorous bronze springs are positioned in between the two jewel bearings. The lead current’s path into and out of the moving coil is also made possible by the spring. The ribbon’s suspension is primarily responsible for the regulating torque.
- Damping: The damping torque is applied to maintain the coil’s motion at rest. An induced damping torque is produced by the permanent magnet’s aluminium core, which is moving between its poles.
- Pointer & Scale: The moving coil and the pointer are connected. The coil’s deflection is detected by the pointer, and the scale displays the extent of the deviation. Because the pointer is composed of a lightweight material, the movement of the coil readily deflects it. When the pointer’s blade is properly aligned, parallax error in the instrument can be easily decreased.
Working Principle
Below we discuss about the working principle of PMMC instrument :
As the current-carrying conductor or coil that is moved is placed between the permanent magnet, this instrument is called a Permanent Magnet Moving Coil. As per Faraday’s law, when we pass current through the coil, the coil starts moving in between the magnet because the magnetic lines of force are passing through the coil. The pointer attached to the coil starts to point on the scale to show the current level. A balancing weight and a spring is also use here to control the position and reposition of the pointer. When current level is become zero then the pointer point on the Zero line because of spring and balancing weight.
Advantages
The following are the advantages of PMMC instrument :
- The scale is correctly divided.
- Power consumption is also very low.
- It also has high accuracy.
- It has high amount of torque to weight ratio.
- It generates less amount of error.
Disadvantages
The following are the disadvantages of PMMC instrument :
- Only use for DC measurement.
- The cost of this type of instrument is high.
Applications
The following are the applications of PMMC instrument :
- Used as Ammeter
- Used as Voltmeter
- Used as Galvanometer
Conclusion | Diploma Engineering Notes | Poly Notes Hub
In this note, we are writing about PMMC Instrument or Permanent Magnet Moving Coil. About the Construction of PMMC Instrument and Working Principle of PMMC also. Our Poly Notes Hub provides syllabus-wise notes for polytechnic or diploma engineering students of streams like Electrical Engineering, Electronics Engineering, Electrical and electronics Engineering, Electronics & Instrumentation Engineering, and Computer Science & Technology. Our website is updating day by day so keep in touch with us for new and syllabus-wise notes and topic which helps you all to do any task regarding diploma engineering.