IP (ingress protection) ratings classify the level that a sensor is protected against infiltration by foreign materials such as dust and water. The first digit of the IP rating indicates the protection level against solids entering a sensor while the second one notes moisture resistance (Table 1). While a zero designates that there is no protection at all, higher numbers identify more stringent defense against elements invading a sensor while operating in a specific environment.

LVDT linear position sensors are typically rated between IP61 and IP69. While dust-tight in virtually all configurations (hence the constant use of the number 6 as the first digit of the IP rating) LVDT sensors have different levels of water ingress protection, based on construction.

For example, some LVDT position sensors are built with limited coil protection, while others are protected with varnish or epoxies. Hermetically sealed LVDTs are welded closed so nothing can intrude the sensor. Each type of LVDT construction bears a different IP rating and may vary by manufacturer. Below are IP ratings for some common LVDTs.

Non-hermetically sealed LVDTs (IP61 rating)
The external sealing of non-hermetically sealed LVDT linear position sensors may meet IEC standard IP61. As these sensors are protected from dust ingress and condensation, they are suitable for use in the following applications:

• dry environments with limited dust/dirt exposure
• laboratory testing, indoor applications
• precision gaging
• dial indicator replacement
• robot actuator position feedback

When coils are completely encapsulated in epoxy, the non-hermetically sealed LVDT position sensors increase their rating to IP64, making them suitable for use in environments where heavy humidity may occur.

Hermetically-sealed LVDTs (IP68 rating)
Constructed entirely of stainless steel, hermetically-sealed LVDT position sensors may incorporate coil windings that are sealed against hostile environments to IEC standard IP68. In addition to being protected from total dust ingress, these sensors can be rated for long-term water immersion up to a specified pressure without water ingress.

Recommended applications for IP-68 rated LVDTs include:

• outdoor structural monitoring
• applications with dust, dirt, grease, humidity
• heavy industrial
• valve position

All sensors rated by manufacturers to achieve IP68 may not be the same but must exceed IP67 ratings. For example, IP68 sensors from TE Connectivity are sealed through welding, with all wetted parts constructed of metal with the exception of the connector. The sensors themselves can be submerged in water or other fluids up to 1,000 psi when not operational. However, they cannot operate while submerged because water could intrude into the mating plug and cause a short.

Submersible LVDTs (IP68)
Submersible LVDTs may be rated at IP68 with appropriate Seacon-Branter mating connector. The connector and mating plug can be rated for pressures up to 5,000 psi or higher.

Typically, these units are designed with a 20-year life for use in critical applications where access to the unit for replacement or repair is very costly.

Recommended applications:
• seawater or fresh water
• dam/bridge structural monitoring
• choke/Christmas tree valve position monitoring
• subsea extensometers
• mooring Cables
• ROV actuator/latch position feedback

TE Connectivity
www.te.com/usa-en/products/sensors.html