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History of the 38999 Connector

Wednesday, April 24, 2019
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Components that are space-bound are the most mission-critical of all aerospace applications. These components are subjected to extreme environments. Manufacturers see to it that such components can withstand shock and exposure to temperature ranges as well as intrusion or contamination of foreign substances like chemicals, water and dust A space craft is subjected to radiation levels as it flies into space.

Components should be able to survive temperature extremes for hot to cold conditions. There is also a potential of collision with other objects in space. Thus, reliability and durability are critical features that these space-bound components must have. The connectors used in space did not evolve overnight. A lot of research and development brought the 38999 connector to where it is right now.
Evolution of the 38999 Connector
The U.S. Department of Defense created the original specifications for the military grade Circular Connector in the 1930s.  This was due to the demand for very severe tactical and aeronautical applications.  These connectors were known as type AN (for Army-Navy).  The original specifications set the standard for the various military circular connectors developed.

MIL DTL 38999 Qualified Products Listed

A forerunner to these circular connectors is the AN5015, also known as MIL-DTL-5015. Subsequent derivatives are known as Military Standard, ML-STD, MIL-SPEC or MS. These type of connectors are extensively used in industrial, commercial, automotive, marine and aerospace applications.

The 5015 connector is very reliable for supporting transmissions of AC and DC power supply. However, the smallest contact (size16) is not suitable for higher frequency signals. Size 20 contact and lower wire gauges (AWG) are needed for such high frequency signal.

Due to this limitation, the MIC-C 26482 and MIL-C 83273 were developed in the 1950s to accommodate size 20 contacts. This type of connector supported power applications and robust transmission of higher frequency signals.

The MIL-C 26482, at that time, was used by the U.S. Navy and in the 1960s the MIL-C 83723 was utilized by the U.S. Air Force. Both connectors were similar in make and properties.

The fast evolution of computer-controlled equipment gave way to the need for a specification that supports higher density insert layouts and smaller contacts. In the 1970s, more signal capability with less power capacity in the I/O connectors was a top priority.  In order to fulfill this requirement, the MIL-DTL 38999 standard was created along with MIL-STD 1560.  These connectors supported contacts down to size 22 which enables high speed data transmission with a smaller gauge wire.
38999 Connectors Series
Versatility is a vital feature of the 38999 connectors.  It was developed with robustness and as a fool-proof input/output circular connector capable of more signal and less power consumption. Having size 22 contacts addresses the capability.

The 38999 specifications define threaded, bayonet and breach coupling mechanisms in four types

Series 1 – A bayonet-coupling system for blind mating. This type can withstand severe wind, moisture issues and high vibration. It is designed in such a manner that it is impossible to damage the exposed contact pins when the mating plug is placed during hasty or careless connection.
Series 2 – Lighter in weight, bayonet-coupled version for use where high vibration is not expected.
Series 3 – A threaded version and with normal mating. Vibration resistant.
Series 4 – Has a breach-lock version for blind mating that requires 900 of rotation to lock. It is also vibration resistant.

Operating range of temperatures for all series are from -65 to +200ºC.
A 38999 connector is comprised of a plug and receptacle, commonly called a mating pair.  The mating pair has a male contact or pin and a female contact called a socket.

hermetic round connectors

The primary connector housing is called a “shell”. A circular connector shell is cylindrical and can be as small as 0.375 to 3.25 inch diameter or larger. 
38999 Connector Uses
The MIL DTL-38999 connectors are primarily designed to withstand the extreme exposure, shock and vibration that Aerospace and Defense applications require.
Defense Applications
  • Communication systems
  • Military aircrafts
  • Vehicle and hand-held platforms
  • Military ground support systems
  • Computer systems
  • Blind-mate applications
  • Low signal, high density platforms
  • Unmanned systems
Aerospace Applications
  • Aircraft engines
  • Aerospace launch vehicles
  • Commercial aviation
  • Electrical testing equipment
AMETEK-EIP manufactures hermetically sealed connectors in accordance with standards set by the MIL DTL-38999 standards.  The Series 9800 is designed to provide low silhouette for minimum size and weight. They are available in both tin-plated mild steel and the 300 series available in stainless steel bodies. Series 9900 of glass-to-metal-seal connectors provide excellent service in areas of severe environments, such as high temperature, humidity, vibration, shock and where EMI/RFI shielding is required.