At first glance, refrigeration may seem an impossibility, at least from the standpoint of thermodynamics. How can you burn energy, increase entropy, and at the same time cause temperature to drop, making for a lower entropy state? The fundamental rule of thermodynamics is that entropy, the measure of disorder, can rise during a period of […]
The principle of impedance matching
Impedance is an umbrella term that includes resistance and both inductive and capacitive reactance. The two reactances are frequency dependent and pull in opposing directions, so to speak. If equal, they cancel out. If unequal, the remainder must be vectorially combined with “straight” resistance to obtain impedance. This quantity, like resistance, is measured in ohms […]
The difference between the NEC and IEC 60364
The National Electrical Code (NEC) contains numerous electrical design and installation procedures as well as many manufacturing requirements. It is re-issued every three years by the National Fire Protection Association, often with extensive new mandates. The NEC is also international. Besides the United States, other countries that have enacted the standard include Mexico, Venezuela, Costa […]
Basics of Helmholtz coils and resonators
Hermann Helmholtz (1821-1894) flourished during a period of the nineteenth century marked by a rapid growth in scientific knowledge, particularly electrical research. His father, Ferdinand Helmholtz, was a close friend of the philosopher Immanuel Hermann Fichte, and because of this association, Herman Helmholtz was exposed to the ideas of Fichte’s great predecessor, Immanuel Kant, whose […]
Basics of Hall effect sensing
The Hall effect, detected and described by Edwin Herbert Hall in 1879, arises when a small voltage appears across a conductor in the presence of a magnetic field. The field is transverse to an electric current in the conductor and to the lines of magnetic flux, which in turn are perpendicular to one another as […]
Electrodes for earth grounding
The National Electrical Code (NEC) permits, in certain very limited situations, installation of an ungrounded electrical system. But even here, as in all electrical work, an equipment grounding conductor is required to establish ground continuity for any non-current carrying metal parts including enclosures, fittings, conduit, and so on. It follows that there must be one […]
Basic electric motor insulation testing
A variety of measuring instruments may be used to detect and diagnose malfunctions in electric motors. In particular, the insulation resistance tester (or megohmmeter), generally known by its trade name Megger, can provide critical information regarding the condition of motor insulation. In an industrial facility, the recommended procedure is to perform periodic tests and record […]
How to use a Megger to measure and test motor insulation
When it comes to checking out electric motors, there are special measuring instruments that may be used to detect and diagnose malfunctions. The insulation resistance tester, generally known by its trade name Megger, is capable of providing critical information regarding the condition of motor insulation. In an industrial facility, the recommended procedure is to perform […]
Induction motor basics
Induction motors are considered asynchronous. This is because while their speed depends upon the external sine wave, it is not precisely synchronized to it. In an induction motor, the ac power supply connects directly to the field coils that are part of the stator. The alternating power produces a rotating magnetic field. This field induces […]
Synchronous motor basics: what you need to know
Rotary electric motors involve the interaction of two magnetic fields, that of the stator and that of the rotor. In a brushed-type dc motor, the dc voltage is applied to the stator, creating a stationary magnetic field. DC is also fed to the commutator, which is attached to the armature, part of the rotor. Because […]