Hermetic connectors suitable for harsh environments

13th June 2017
Alice Matthews

In order to meet specific requirements for aircraft, military equipment, and applications in harsh environments, Esterline Connection Technologies – SOURIAU has announced that its range of circular connector with thermocouple contacts now includes a version with hermetic receptacle. This connector range supplements and complements SOURIAU's current range of hermetic connectors and thermocouple contacts. The specific thermocouple contacts can be fitted in connectors that comply with EN 3646, MIL-DTL-26482, MIL-DTL-38999, and EN 2997.

In civil and military aviation, for example, they are used to connect temperature sensors placed around aircraft engines and brake systems.

A specific contact technology
In temperature measurement chains, nickel-chrome (NiCr) and nickel-aluminium (NiAl) are soldered at the sensor inside the transducer and must have material continuity up to the analysis electronics. A connector's contacts must meet this requirement in order for it to be added to the measuring chain. SOURIAU ensures material continuity by fitting a nickel-chrome contact and a nickel-aluminium contact in each of its thermocouple connectors, thus rendering them neutral in the measuring chain.

Hermetic contacts and receptacles
Receptacles fitted on equipment must be hermetic at two points. The first point relates to the method used to attach the receptacle, which is possible by laser or TIG welding or by fitting a special O-ring. The second point is at the contacts inside the receptacle. Here, the conventional insulator is replaced by a glass insulator. A sintered pad of the same size as the shell and corresponding to the contact layout is inserted and melted at 1,000°C in an autoclave. The heating and cooling cycles in the process are interspersed with stabilisation periods. As a result, the glass contracts to form a fully hermetic seal within the shell and around each contact. Each connector undergoes rigorous quality control in the form of a helium leak test in order to guarantee the specific leakage rate of less than 10-7atm-cc/sec required for hermetic connectors.

Contact layout and arrangement
Most connectors are fitted with a pair of nickel-chrome/nickel-aluminium contacts to form a thermocouple pair. SOURIAU can provide connectors with two pairs or more of thermocouple contacts for customers that require signal acquisition redundancy.

Two standard arrangements of three and five contacts are available based on standard definitions. As in any hermetic connector, the matching contacts are typically made of ferronickel.

SOURIAU can customise the location of contacts inside the cavity to the customer’s requirements.

Available connectors
SOURIAU's hermetic connectors with thermocouple contact are now available in three versions: EN 2997, MIL-DTL-38999 Series III, and EN 3646.They are a suitable match with SOURIAU's existing range of hermetic connectors and removable contacts designed for use in increasingly harsh environments.

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