Issue 132 July 2001
Inductive Sensors

The rapid pace of change in technology constantly calls for upgrades and more variety of products. This month, George focuses on the next big thing for position sensors. So, read on to get the skinny on the newest development before it makes it to the mass market.

Start • LVDT Revisited • The Works • Electrical Interfaces • Mechanical Interfaces • The Future • Sources & PDF

Accurate, reliable position sensing is the backbone of many closed-loop control systems in robotics, automotive, and industrial process industries, to name a few. In May 1999, I introduced you to the principles behind the popular variable differential transformer sensors, the LVDT (linear variable differential transformer) and its close relative RVDT (rotary variable differential transformer), the reigning family of position sensors. [1] These devices have changed little in their 100-plus years, so the question is: Are there any new devices more in line with today’s technology that could lay claim to being the next dominant generation of position sensors?

The answer is a qualified yes. When it comes to operation in extremely hostile environments, such as the cryogenic temperatures encountered in space, or the mere –65°C in the arctic and at high flying altitudes, or the hundreds of degrees heat inside engines, it is hard to beat the variable differential transformer. Not much can happen to a stationary, wire-wound bobbin, which is all the LVDT is. I’m not aware of any new sensor technology that could successfully challenge the LVDT’s position in these extreme environment applications any time soon.

In the friendlier environment between –40°C and 125°C, however, several contenders already exist. Optical encoders, Hall effect, and magneto-resistance (MR) sensors for example, have been around for some time. New developments such as piezoresistive beam have been introduced, but they still have to prove their capabilities.