A switch seems like a simple, humble device. But actually, the topic quickly becomes complex, especially for switches subject to National Electrical Code provisions. The NEC defines several types of switches: • A bypass isolation switch is a manually operated device used in conjunction with a transfer switch to provide a means of directly connecting […]
Basics of waveguides, microwaves, and ovens
Because series inductive and parallel capacitive reactances rise with frequency, coaxial cable cannot be used when the frequency of the signal is above a specific level. This is also a function of the length of the run and it depends upon the application, i.e. how much loss can be tolerated. The upper limit, therefore, varies […]
Basics of solid-state biasing
Many solid-state devices, like the earlier vacuum tubes that they have largely replaced, require a unvarying dc voltage applied at one or more specific terminals. This is known as a bias. In an amplifier, for example, the voltage coexists with the varying ac signal that is applied at the same terminal. With the ac signal […]
Motor nameplate and brushless motor basics
The brushless dc (BLDC) motor is taking over ever more applications formerly consigned to ac and brush-type dc motors. The reason is that electronic rather than mechanical formats are more efficient, quieter (acoustically as well as in regard to EMI) and require less maintenance. The traditional dc motor became widely available in the second half […]
Basics of interferometers
Interferometers figure prominently in the history of experimental physics. They were at the heart of the Michelson-Morley Experiment of 1887 that attempted unsuccessfully to detect the existence of an ether wind, a hypothetical medium for light transmission. (The null result was not because of any inadequacy in the instrumentation or deficiency in the design of […]
Particle spin and energy efficient electronics
We all know that the earth, like many spherical bodies, turns on its axis. It is said to have angular momentum. The spin velocity does not change, slow down or speed up, unless force or friction is applied. This principle is illustrated by that wonderful nineteenth-century mechanism, the centrifugal fly-ball governor, used to regulate precisely […]
Basics of variable-frequency motor drives
DC motors have historically had advantages in that their speed and direction of rotation could be easily controlled by adjusting or switching the supply voltage. This has made them well-suited for elevators, ski-lift drives and similar applications requiring smooth and reliable operation. Compared to equivalent dc motors, three-phase induction motors are relatively lightweight and inexpensive […]
Basics of frequency mixing and mixers
When two waves – sound, electrical, in water – that are of different frequencies are conveyed in the same medium, the alternating constructive and destructive interference gives rise to sum and difference frequencies. If acoustic tones are close to the same frequency, the resultant difference signal will be heard as a distinctive beating sound that […]
Basics of intrinsically safe wiring
The National Electrical Code (NEC) distinguishes between classified and unclassified locations. Classified locations are potentially hazardous where there is electrical usage because the atmosphere contains or may due to mishap contain explosive gas, flammable liquid vapors, dust or flammable airborne material. The NEC specifies electrical materials, devices and installation methods for these areas. The requirements […]
Ten good internet sites for test engineers
You can often find the answer to a specific question or research an extensive area of interest on the Internet. Here are ten Internet resources that electronic professionals may find useful: 1. Wikipedia still has a reputation for providing fundamentals on just about any technical subject. Electronics has always been a focus, and as time […]