To engineers schooled in modern motor control methods, it may be hard to grasp why three-speed fans designed to move air around in a room can be inexpensive. After all, these fans are powered by as motors, and the go-to method for changing the speed of industrial ac motors is via variable-frequency drives. VFDs work […]
What’s a ring tester and why do you need one?
If you one day find yourself with a transformer that might or might not have a shorted winding, your first inclination for verifying your suspicions might be to find an inductance meter. The problem with powering up an inductance meter for this situation is that the inductance of a transformer containing a shorted turn might […]
Making better oscilloscope measurements through horizontal and vertical scaling
Early oscilloscope models were primitive by modern standards. Among the first major innovations was triggered sweep, introduced by Tektronix just in time for the post-World War Two electronics boom. This improvement in waveform imaging synchronized successive periodic waveforms to create a coherent image, based on a uniform level along the rising edge or another user-defined […]
Traceability and the hierarchy of calibration
Advances in the science of measurement are simplifying the task of accurately quantifying uncertainty. Michael Brown, Fluke Calibration Accurate measurements are critical to every aspect of our lives; that’s why metrology is the oldest science in the world. Our ability to understand the world around us depends on how well we can measure it. As […]
What are the telegrapher’s equations?
You can thank Oliver Heaviside (actually a short, thin man), for the telegrapher’s equations (or just telegraph equations). These are probably better known as the transmission line equations. They are actually a pair of coupled, linear partial differential equations that describe the voltage and current on an electrical transmission line with distance and time. RF […]
Can you tell the difference between an electrolytic and super capacitor?
If you disassemble an electrolytic capacitor and a supercapacitor, you might have trouble distinguishing differences between the two unless you had a practiced eye. Physically, the two can resemble each other though their electrical performance differs drastically. First a few basics. Ordinary capacitors, of course, are characterized by metal plates separated by a dielectric. In […]
What to look for during instrument calibration
When you send an instrument to a calibration lab, what do you expect to happen? The comprehensive definition of calibration is a verification of instrument specifications by measuring actual performance using external lab standards, normally instruments, which have better performance than the thing they’re measuring and which are traceable to the International System of Units […]
How to screw up a capacitance measurement
Consider the task of performing a capacitance test using an LCR meter or a good multimeter such as the Fluke 287 True RMS Multimeter. If the capacitor under test is an electrolytic or film-based device, the main measurement concern is often just ensuring the capacitor is not under power or doesn’t have a stored charge–electrolytics […]
Selecting and applying programmable power supplies
A system-level view of testing is helpful when specifying power requirements. Jeff Brakley • Ametek Programmable Power Inc. There are numerous options available for programmable dc power supplies. Users can select from a wide range of voltage, current, and power ratings. Other specifications include input voltage, output voltage regulation, output ripple and noise, and transient […]
Why won’t it work? A look at antiresonance
A clock generator generally consists of a resonant circuit and an amplifier. Resonance occurs in an electrical circuit when XL = XC. At this juncture, the imaginary component of the transfer function is zero. A resonant circuit oscillates at a specific frequency. Like certain other electrical phenomena, it is capable of generating higher voltages or […]