An LVDT Linear Position Sensor inadequately protected against humid or corrosive atmospheres will entrap moisture in the coil, resulting in improper operation and failure. To avoid such problems, the windings of standard LVDTs are vacuum-impregnated with an insulating varnish that resists humid environments and the deteriorating influence of temperature cycling. A hermetically sealed assembly with a heavy-wall, metal housing also ensures outside media does not enter the windings, making LVDTs impervious to dirt, water, steam, chemicals, and even extreme temperatures that can, otherwise, shorten sensor life or reliability.
For severe applications involving extreme exposure to humidity, condensation, spray, salt atmospheres and similar environments, the coil windings of a standard LVDT Sensor may be further protected with special potting compounds or encapsulating resins. For high-temperature operation, vacuum-impregnation with moisture-resistant silicon varnish is possible. Leads can be sealed with a glass-sealed header or compression bushing, stainless steel sheathing, or Teflon coated so connections don’t fail in extreme environments.
Lack of leakage resistance can prevent accurate LVDT operation even though individual winding measurements (inductance and resistance) appear unaffected. Even a leakage resistance as high as 100 megohms (MO) may cause noticeable performance deterioration in critically adjusted, phase-sensitive circuits such as those of AC null-balance systems. For this reason, care is taken to ensure that the typical LVDT will show at least 1,000 megohms (MO) insulation resistance at 70ºF between any two windings or between any winding and the metal case.
Macrosensors offers a tutorial and position sensor selection guide online to provide more information about LVDTs.