Electronic connectors on medical equipment must meet stringent requirements. They have to guarantee signal reliability in the face of harsh duty and tolerate frequent sterilizations. They must also be small, lightweight, easy-to-use, and fool proof. And some applications need connectors made of nonmagnetic materials.

Medical connectors also have to survive demanding situations. Connectors used in patient monitors in ambulances, for example, must tolerate shocks and vibration that stationary systems will never see. System developers must also consider the number of mating cycles connectors will likely endure. For instance, high-quality industrial connectors may be expected to reliably mate up to 500 times, but they won't withstand a lifetime of 100,000 mating cycles. The higher figure is more typical for patient monitoring systems, where connectors are plugged in and pulled out many times a day over many years.

The right contact

A connector's contact design tends to dictate the number of mating cycles it can withstand. Conventional cantilever-beam mechanisms, for example, are points of vulnerability in some connectors. A high normal force, and therefore high-insertion force, necessary for a good connection, tends to wear out the spring in this mechanism. An alternative design with hyperboloid contacts, based on a wire-basket design, avoids the cantilever spring. Smooth, low-force wiping action of the pin entering the socket ensures such connectors withstand up to 100,000 mating cycles.

Several schemes can prevent hospital staff from hooking up cables to the wrong plug. Color-coding, for one, provides visual indications of correct matches between plugs and receptacles. This coding is usually determined when connectors are first bought. They have to be manufactured with a particular color-plastic housing. In more flexible systems, however, the user can choose the color coding by using interchangeable colored silicone rings for the receptacle and similarly colored strain-reliefs for the plug.

Another safeguard against incorrect mating is to key the connectors. Adapting a physical mechanism to the connector, such as a spline, prevents mating between unmatched plugs and receptacles. It is possible to purchase connectors that are identical in every respect, except for different keying positions.

Connectors with a customer-keyable function provide even more flexibility. Plastic elements prevent mismating plug and receptacle while protecting the contacts. The keying piece can be snapped in one of six ways. Such a customer-definable feature means system developers can assign compatibility between connectors as designs progress. Another plus: Customer-keyable connectors reduce inventory costs over conventional keyed designs.

Materials

Much of the equipment used in patient monitoring must be cleaned or sterilized before each use. It is important that connectors withstand the various sterilization methods, including soap and water, bleach, alcohol, ethylene oxide gas, gamma radiation, and high-temperature steam autoclaving. These methods degrade some standard connector materials, so it's critical the connector manufacturer takes sterilization into account when choosing materials for medical connectors.

Lastly, the drive to improve magnetic resonance imaging scanners has prompted some suppliers to provide nonmagnetic connectors and other components. Any magnetic component near the RF coil in a scanner tends to cast shadows on images. One obvious solution is to specify high-reliability connectors made from nonmagnetic materials.