LVR, a Temperature Independent Alternative to LVDT’s in Harsh Environments

These advantages are possible due to the fundamental design of the sensor. The LVR sensor consists of a coil wound on a round ceramic tube as shown above. The initial layer of wire is wound as a helix with a large pitch. Upon reaching the end of the tube, the pitch is reversed, and a returning reverse helix is laid over the first coil. The two ends of the double coil are attached via separate cables to remote electronics, forming a resonant circuit that oscillates in the 2 – 4 MHz region.  The two coils are now wired in series with current flowing clockwise in one coil and counterclockwise in the other.  The magnetic field of each coil, as determined by the right-hand-rule, are parallel to the sensor but point in opposite directions and thus cancel each other. At the same time, also by the right-hand-rule”, the electric fields  are perpendicular to the sensor and thus are additive.   The resulting electromagnetic field outside the coil is a strong electric field with minimal magnetic component.  Thus a metal rod attached to the item to be measured will change the frequency in a rapid and predictable manner.

The resonant frequency of this circuit is determined by the formula