Facebook Twitter. The permanent magnet moving coil instrument is the most accurate type for dC measurements. Working principle of pmmc instrument is the same as that of the d'Arsonval type of galvanometers, the difference being that direct reading instrument is provided with a pointer and a scale. Construction of pmmc instruments:.
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There are different electrical machines are used in the ship so that it can travel from place to another safely as well as capably.
But these machines need maintenance while traveling to avoid any type of breakdown. To measure different electrical parameters on the ship, different instruments are used so that we can check the machines to maintain their proper working condition. Similarly, an instrument like PMMC permanent magnet moving coil is frequently used on ships as well as different applications. This article discusses an overview of the PMMC instrument.
This instrument is simple as well as most frequently used on ships with sophisticated names. These instruments are used when an exact measurement is required as well as to aid while maintaining electrical equipment. These instruments use permanent magnets to create the stationary magnetic field in the coils, and then it is used with the moving coil that is connected to the electric source for generating deflection torque according to the Fleming left-hand rule theory.
The PMMC instrument working principle is when the torque is applied to the moving coil that is placed within the permanent magnet field, and then it gives a precise result for DC measurement. After that the magnetic field will be in the forefinger, flow of current will be across the middle finger and finally, the force will be through the thumb finger. Once the current flow within the coil on the aluminum former, the magnetic field can be generated in the coil in proportion to the current flow.
The electromagnetic force throughout the fixed magnetic field from the permanent magnet generates the deflection force within the coil. After that the spring generates the force to resist additional deflection; therefore it helps to balance the pointer. So damping force can be generated within the system through the aluminum core movement of the magnetic field. It maintains the pointer stable to a point. The construction of the PMCC instrument can be done using several parts where the permanent magnet and moving coils are essential parts.
Each part of this instrument is discussed below. It is an essential component of the PMMC instrument. The designing of this coil can be done by wounding copper coils to a rectangular block among the magnetic poles. It is made with Aluminum and the rectangular block can be called Aluminum former rotated into the jeweled bearing. So it permits the coil to turn freely. Once the current is supplied throughout these coils, then it gets a deflection within the field, then it is used to find out the voltage or current magnitude.
The aluminum is a non-metallic former, used to measure the current whereas the metallic former including high electromagnetic damping is used to calculate the voltage. In several designs, an extra soft iron cylinder can be arranged among the magnetic poles to create the field identical; while decreasing air reluctance for increasing the strength of the field.
In the PMMC device, the torque can be controlled due to the springs which are fabricated with phosphorous bronze. These springs are arranged among the two jewel bearings. The torque can be controlled mainly due to the delay of the ribbon. So the pointer can be kept at rest after the early deflection.
It assists in the right measurement devoid of fluctuations. Because of the movement of the coil within the magnetic field, eddy current can be generated within the aluminum former. This generates the damping force otherwise torque to resist the motion of the coil.
Gradually the deflection of the pointer will be reduced and lastly, it will stop at a permanent position. In this instrument, the connection of the pointer can be done through the moving coil. The magnitude of their derivation can be displayed on the scale. The pointer within the instrument can be designed with lightweight material.
In a PMMC instrument, different errors can be occurred due to the temperature effects as well as getting older of the instruments.
The errors can be caused by the main parts of the instrument like the magnet, effect of temperature, moving coil and the spring. So, these errors can be reduced when the swamping resistance is connected in series using the moving coil. Here, the swamping resistance is nothing but the resistor which includes less temperature coefficient. This resistance can reduce the temperature effect on the moving coil.
The equation involved in the PMCC instrument is the torque equation. The restoring torque can be provided to the moving coil can be done with the spring and it can be expressed as. From the above equation, we can conclude that the deflection torque can be directly proportional to the flow of current in the coil.
These instruments measure the average value and the value of AC is zero. It works on the principle of electromagnetic effect. The torque that turns aside the pointer over a scale based on the flow of current throughout the instrument.
Thus, this is all about an overview of the PMMC instrument. These are sensitive, accurate and these instruments work for a long time without maintenance and defects. Here is a question for you, what are the alternative names of the PMMC instrument? Share This Post: Facebook. What is Metadyne : Working and Its Applications.
PMMC Instrument; Construction, Working and Application
There are different electrical machines are used in the ship so that it can travel from place to another safely as well as capably. But these machines need maintenance while traveling to avoid any type of breakdown. To measure different electrical parameters on the ship, different instruments are used so that we can check the machines to maintain their proper working condition. Similarly, an instrument like PMMC permanent magnet moving coil is frequently used on ships as well as different applications. This article discusses an overview of the PMMC instrument. This instrument is simple as well as most frequently used on ships with sophisticated names.
Permanent Magnet Moving Coil or PMMC Instrument
The permanent magnet moving coil instruments are most accurate type for direct current measurements. The action of these instruments is based on the motoring principle. When a current carrying coil is placed in the magnetic field produced by permanent magnet, the coil experiences a force and moves. As the coil is moving and the magnet is permanent, the instrument is called permanent magnet moving coil instrument. The amount of force experienced by the coil is proportional to the current passing through the coil. The moving coil is either rectangular or circular in shape.