Position sensing apparatus having internal target rod with remote electronics for harsh environments

A sensing apparatus for use in harsh environments to measure a characteristic of an electrically conductive target, the apparatus comprising:

• a sensing element formed as a section of a coupled slow-wave structure including a hollow ceramic tube and at least two impedance conductors each curled into a helix or spiral with opposing directions of winding around the hollow ceramic tube to form a resonator, the sensing element providing as an output signal a digital frequency that depends on the value of the measured characteristic of the target;
• an internal target rod formed of an electrically conductive material and configured to move into and out of the sensing element, being covered and uncovered by portions of the sensing element;
• an electronics module including a resonant oscillator, a frequency meter, and a microprocessor configured to receive the output signal from the sensing element and display the characteristic of the target;
• and
• at least two coaxial cables each having a length and being connected to one of the at least two impedance conductors on one end and to the electronics module on the other end, so that the electronics module is attached directly to the sensing element through the at least two coaxial cables, with the length of the coaxial cables separating the electronics module from the sensing element by a distance sufficient to avoid exposing the electronics module to the harsh environments,
• wherein the apparatus is intrinsically safe and is configured to operate in a harsh environment having a temperature of at least 225° C.