How a DC Magnetic Motor Control Works
Author: Chet Val
As manufacturing and industrial facilities evolved over the years, so have the ways we power the machinery. By power, I am referring to the controlling or initiating motion to perform a process. The key here is the industrial motors themselves. Whether they're small, medium, or large, motors need to be controlled. They need to be started, stopped, and varied in overall speed for safety and also to properly perform their selected function. A motor rotating at unsafe speeds can be hazardous to personnel and dangerous to the equipment to which they are connected. The motor controller comes into play to do just that. Control of the startup as well as the acceleration to an appropriate speed, then the monitoring of the motor to ensure it is operating within its power rating, and of course the stoppage of the motor. For decades, a magnetic dc motor control was the most efficient way to get the job done. These sometimes complex circuits composed of relays, contactors, timers, and resistors could be found anywhere there was an industrial electric motor. At the time, they were new technology replacing drum controllers which used the human element to control a motor's acceleration. on these controllers, an operator had the responsibility of turning on the motor and bringing it up to its proper speed using a handle attached to a drum of contacts. The faster the operator turned the handle, the faster the motor accelerated. Operating speed for the motor could also be controlled using the handle by stopping at a certain position short of full deflection. Motors could also be reversed using these controls by turning the handle in the opposite direction. Drum controllers relied too much on an operator's gentle touch to be efficient and safe. The dc magnetic controller easily became the accepted method of motor control in its time.
Other optional items added to these magnetic motor starters were components like external current meters for personnel to observe. A load meter is a good example of current monitoring modified to display the load on the motor in real time to the operator. There were also reversing options which enabled the direction of the motor to be changed with a switch or by turning a mechanical handle. With a familiarity of magnetic dc motor starters and basic electrical skills, troubleshooting the control circuits of any of these manufacturers becomes easier with experience because the concept and basic schematics from Cutler Hammer, GE, Allen Bradley, and Westinghouse were always similar.
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About the Author
Chet is an associate of Obsolete Industrial Parts, an informative site dedicated to locating obsolete parts for industrial equipment including dc magnetic motor controls, servo motors, obsolete plc's, switches, and a host of other parts. Their official website obsoleteindustrial.com is owned and operated by Val Marketing of Carbondale, PA.
In physics, a magnetic field is that part of the electromagnetic field that exists when there is a changing electric field. A changing electric field can be caused by the movement of an electrically charged object, as in an electric current; or a combination of the orbit of an electron around an atom and the spin of electrons themselves, as in a permanent magnet.
Definition:
A magnetic field is the relativistic part of an electric field, as Einstein explained in 1905. When an electric charge is moving from the perspective of an observer, the electric field of this charge due to space contraction is no longer seen by the observer as spherically symmetric due to non-radial time dilation, and it must be computed using the Lorentz transformations. One of the products of these transformations is the part of the electric field which only acts on moving charges – and we call it the “magnetic field”.
The quantum-mechanical motion of electrons in atoms produces the magnetic fields of permanent ferromagnets. Spinning charged particles also have magnetic moment. Some electrically neutral particles (like the neutron) with non-zero spin also have magnetic moment due to the charge distribution in their inner structure. Particles with zero spin never have magnetic moment.
A magnetic field is a vector field: it associates with every point in space a (pseudo-)vector that may vary through time. The direction of the field is the equilibrium direction of a magnetic dipole (like a compass needle) placed in the field.
Does anybody know what an Electro magnetic field meter is?
i like the TriField natural EM meter, however I dont know where I can get one in Canada?????
ive searched yahoo and google for canadian suppliers of the Trifield Natural Meter and for gauss meters… i have called several dozen electricians and they have no clue what a guass meter OR a trifield meter is.ug!
what is the effect of magnetic field on electronic meter?
Up to what level of field ,can a precision meter reads without error ?
East of the wire the magnetic field is UP
and it magnitude = µo*I/2πr = 2.0×10^-7*3A/0.10m = 6.0×10^-6T
Electronic electricity meters are increasing in popularity all over the world. Free from mechanical wear and tear, they permit remote reading, are network-enabled and support multiple tariffs. However, rising energy costs are accompanied by an increase in the number of cases where meters of this type are subjected to manipulation. External magnetic fields can be used to influence the measuring circuit and reduce the power consumption registered. Although obtaining large permanent magnets with high magnetic induction was extremely difficult in the past, today such magnets are relatively easy to find.I am sure you are not trying to ….
A soft iron case protects its contents from a magnetic field. Non-magnetic materials like plastics and most metals don’t. A friend of mine used to reduce his electricity bill by placing a strong permanent magnet next to the case, near the rotating disc. It slowed down the disc and saved him money. Of course, you need a window of glass or transparent plastic to see the disc, and these are non-magnetic materials. If some smartass energy marketing employee wants to prevent this sort of thing, the only way I can think of that they could do it would be to enclose the rotating disc in an iron box and run wires out to a digital display that has a window, so you can see it. Don’t tell the bastards that. I’m in favour of ripping off power companies.
Energy meter slow down in magnetic field.Which is better metallic casing or engg. plastic to protect the meter
metallic casings are now replaced by poly carbonate material.Will it help to reduce the external magnetic effect?
Energy meter specification says it should withstand .5 testla magnetic field.Is it sufficient ?
Energy meter slows down in magnetic fld.The above spec is substandard as far as present scenario are concerned.
A 10 meter long wire carries a current of 3A to the south. What is the magnetic field strength and direction a?
A 10 meter long wire carries a current of 3A to the south. What is the magnetic field strength and direction at a point that is 10 cm to the east of the wire?