Question
Download Solution PDFThe deflecting torque in a PMMC instrument is proportional to ________.
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFPermanent Magnet Moving Coil (PMMC)
PMMC is used to measure an average DC value of electrical quantity.
The PMMC instrument has a linear scale, hence the deflecting torque produced is directly proportional to the current.
Td ∝ I
The controlling torque in PMMC instruments can be produced by either spring control or gravity control.
For spring control: Tc ∝ θ and For gravity control: Tc ∝ sin θ
The damping torque in the PMMC instrument is provided by eddy current damping.
Advantages
- The PMMC consumes less power and has great accuracy.
- The PMMC has a high torque to weight ratio.
- It produces no losses due to hysteresis.
- It has efficient damping characteristics and is not affected by a stray magnetic field.
Disadvantages
- The moving coil instrument can only be used on the D.C. supply as the current reversal produces a torque on the coil.
- It may show an error due to the loss of magnetism of the permanent magnet.
Last updated on Jul 1, 2025
-> SSC JE Electrical 2025 Notification is released on June 30 for the post of Junior Engineer Electrical, Civil & Mechanical.
-> There are a total 1340 No of vacancies have been announced. Categtory wise vacancy distribution will be announced later.
-> Applicants can fill out the SSC JE application form 2025 for Electrical Engineering from June 30 to July 21.
-> SSC JE EE 2025 paper 1 exam will be conducted from October 27 to 31.
-> Candidates with a degree/diploma in engineering are eligible for this post.
-> The selection process includes Paper I and Paper II online exams, followed by document verification.
-> Prepare for the exam using SSC JE EE Previous Year Papers.