Non-contact sensing of a nearby object’s linear or rotary position in an electrically and mechanically harsh environment is a common system requirement. There are several ways to meet this objective, including sensors based on the Hall effect, the magnetorestrictive effect, and magnetic coupling. One widely used approach is inductive proximity sensing, which is effective, accurate, […]
LVDT electronics, Part 2: interface circuitry
The interface electronics for the LVDT must excite the primary-side winding with a sine wave and then demodulate the two resultant secondary-side waveforms; modern ICs make this analog-signal process fairly straightforward. Part 1 of this FAQ looked at the basics of LVDT excitation, demodulation, and waveforms. This part looks at two standard ICs which implement […]
LVDT electronics, Part 1: excitation and demodulation
The interface electronics for the LVDT must excite the primary-side winding with a sine wave and then demodulate the two resultant secondary-side waveforms; modern ICs make this analog-signal process fairly straightforward. The first two parts of this LVDT article (see References) looked at the LVDT transducer itself, along with its attributes and history. This second […]
Kelvin 4-Wire sensing solves the “IR Drop” problem
Novice engineers usually don’t learn about this problem and its solution in school, but “practicing” ones learn about it soon enough! Problem: I need to determine the change in resistance of a low-resistance sensor located many meters away. My plan was simply to apply a known voltage across the thin-wire sensor leads and measure the […]
LVDT position sensor, Part 2: Characteristics
The linear variable differential transformer (LVDT) is a widely used, inherently rugged, linear-position sensor offering accurate and consistent performance over a wide span of distances. Part 1 of this FAQ looked at the basic operation of the LVDT. This part looks at some of its other performance attributes and characteristics. Q: What does an LVDT […]
LVDT position sensor, Part 1: basics and principles
The linear variable differential transformer (LVDT) is a widely used, inherently rugged, linear-position sensor offering accurate and consistent performance over a wide span of distances. Sensing of physical position is among the most commonly needed parameters in industrial, military/aerospace, robotics, scientific measurement, and control applications, and there are many sensors in use to accomplish this. […]
What are cryogenic temperature measurements? Part 2
Part 1 of this article looked at sensing and sensors for ultracold and cryogenic temperatures; Part 2 advances the story to more esoteric situations. Q: What’s the fundamental difference between measuring extremely high temperatures versus cryogenic ones? A: When things get really hot, extending into thousands of degrees, the sensor options are limited. Usually, it […]
What are cryogenic temperature measurements? part 1
Cryogenic temperatures may seem only of limited interest, but they are actually critical in many instrumentation and other systems. Measuring these ultralow temperatures is both easy and difficult, depending on temperature, material, and mass. Temperature is the most commonly measured physical variable, whether it’s just to assess the local weather to manage the performance of […]