Macro Sensors. In applications where sensors are surrounded by corrosive or pressurized media, a hermetically-sealed LVDT is recommended to ensure outside media does not enter the windings, making units impervious to water and chemicals that can shorten sensor life or reliability. These types of LVDTs feature a hermetically-sealed assembly with a heavy-wall, metal housing and integral metal bore liner either made from 316 Stainless Steel or Super Nickel Alloys. This construction allows free movement of the core while sealing out the surrounding media from the windings.
In addition to its heavy-duty housing, bore liner and end washers are welded together to form a hermetic seal free from oxidation producing faults that may cause leakage. Sensor coils are wound on a one-piece hollow form of thermally stable, glass reinforced polymer, encapsulated against moisture, wrapped in a highly permeable magnetic shield, and, then, secured in a cylindrical metal housing. For severe applications, the coil windings may be further protected with special potting compounds or encapsulating resins. Leads can be sealed with a glass-sealed header or compression bushing, sheathed in stainless steel sheathing or Teflon coated so connections don't fail in extreme environments. Typical hermetically-sealed LVDTs can withstand operating pressures up to 3000 psig. The hermetically sealed construction also lets the core to withstand temperatures up to 400°F.