What is the principle of PMMC instrument?
Definition: The instruments which use the permanent magnet for creating the stationary magnetic field between which the coil moves is known as the permanent magnet moving coil or PMMC instrument. It operates on the principle that the torque is exerted on the moving coil placed in the field of the permanent magnet.
Why PMMC works only on DC?
because pmmc instruments measure- avarage value and avarage value of a.c is zero so that ,pmmc Meter’s pointer does not move. PMMC type instrument uses two permanent magnets in order to create stationary magnetic field.
What is PMMC full form?
A Permanent Magnet Moving Coil (PMMC) meter – also known as a D’Arsonval meter or galvanometer – is an instrument that allows you to measure the current through a coil by observing the coil’s angular deflection in a uniform magnetic field.
Can PMMC be used to measure AC?
PMMC instruments are only used for measuring the DC quantities and it gives the average of value of the quantity being measured. If we apply AC current to these types of instruments, the direction of current will be reversed during negative half cycle.
Which instrument is used only for DC?
Permanent Magnet Moving Coil (PMMC) is only used for DC measurements. Moving Iron (MI) type instruments can be used for both AC & DC measurements.
What material is magnet of PMMC made of?
The Alcomax and Alnico material are used for creating the permanent magnet because this magnet has the high coercive force (The coercive force changes the magnetisation property of the magnet). Also, the magnet has high field intensities. Control – In PMMC instrument the controlling torque is because of the springs.
Which torque is used in PMMC meter?
The controlling torque is provided by two phosphorous bronze flat coiled helical springs. These springs serve as a flexible connection to the coil conductors. Damping is caused by the eddy current set up in the aluminium coil, which prevents the oscillation of the coil.
What are the advantages of PMMC?
The PMMC has a very high accuracy. The PMMC is free from hysteresis error. The PMMC has efficient damping characteristics and is not affected by stray magnetic field. Extension of instrument range is possible with the help of shunt and series resistances.
What is a Megger used to measure?
A megger is used to measure insulation resistance and it is powered by a inbuilt DC generator or battery of a higher voltage range, it is called Megohmmeter.
What is PMMC diagram?
The basic PMMC instrument diagram is shown below. A rectangular coil of thin wire with some turns is wound on an aluminum frame, which has an iron core inside. It is placed between the U-shaped permanent magnet poles, which are made up of Alnico (magnetic alloy).
What is damping system in PMMC?
Damping: Damping torque in PMMC instruments are produced by the movement of Aluminum former in the magnetic field of Permanent Magnet. Due to movement of Aluminum former an eddy current is developed on the former which produces a damping torque.
Which damping is used in PMMC?
eddy current damping
In PMMC instruments, the damping torque is provided by eddy current damping since the presence of a permanent magnet.
What is megger value?
It gives an idea of an insulator’s condition. It is measured using an instrument named Megger test capable of impressing D.C. voltage between its two probes, automatically calculating and then displaying the IR value. Megger test being so popular that “Insulation Resistance” and “Megger Test” are synonymously used.
Is PMMC a galvanometer?
Which torque is used in PMMC?
What is PMMC control torque?
The control torque in PMMC instrument is provided by two phosphor bronze hairsprings. These springs also allow the current to flow in and out of the coil. The control torque produced is equal in magnitude but opposite to that of deflection torque, for the pointer to reach the steady-state position.
Is megger DC or AC?
Megger is an instrument used for measuring insulation resistance of a cable, but the cable that is to be tested is used in AC lines and the megger uses DC as the testing voltage.
What is the working principle of PMMC instrument?
The PMMC instrument working principle is based on the principle of the motor. When the current-carrying coil is positioned in the magnetic field produced by a permanent magnet, then a force is experienced by the coil and moves. This is called the D’Arsonval principle.
What is the construction of a PMMC?
Figure 1 shows the basic construction of a PMMC instrument. A moving-coil instrument contains principally of a permanent magnet to offer a magnetic field and a small lightweight coil pivoted within the field.
What is a permanent magnet moving coil (PMMC)?
Different instruments are used onboard for measuring several electrical parameters to analyze and keep these machines in proper running condition. A permanent magnet moving coil (PMMC) is one such instrument that is popularly used onboard and has several applications.
How does the damping force work in PMMC instruments?
In the case of the PMMC instruments, the damping force uses eddy currents. To facilitate this, the coil is wound on an aluminum frame or coil former in which eddy currents are generated by any rapid movements of the coil in the magnetic field.