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A guide to specifying medical connectors

Feature

By David Phillips, Managing Director, Binder

Medical devices based on electronics technology can cover everything from disposable, one-time-use devices, to handheld diagnostics and bed-side patient monitoring and large CT and MRI scanning systems. While specifying electronic connectors for these medical applications requires the same consideration as for many other applications, there are some factors that are unique to the medical market.

There are some basic choices to be made concerning the electrical and physical attributes that are both directly related and fundamental to connector choice. The current, voltage and the number of contacts, together with the cable diameter and level of shielding required all have a direct influence on the connector choice as do the physical characteristics relating to how the connector will be terminated, the method of mating and the space available both inside and outside the product.

Electrical requirements

The connector’s rated and impulse voltages are defined according to IEC60664-1 – a basic safety standard to achieve insulation coordination – specifying clearances, creepage distances and solid insulation, taking into account the voltage stress and surge together with the expected degree of pollution. These factors determine the physical dimensions of the connector.

The current carrying capacity of a connector denotes the current that can be carried continuously and simultaneously through all its contacts, and is determined by IEC 60512-5-2. The current carrying capacity is not fixed and decreases with increasing ambient temperatures.

Certain applications such as MRI equipment call for shielding against electromagnetic interference (EMI), necessitating screened cable systems that require connectors with good shielding characteristics, offered by metal-bodied or metalised, plastic connectors.

Locking systems and ingress protection

How often the connector will be mated and its IP protection requirements have a major influence on the type of mating system; the chosen method will most likely have a big impact on connector cost. The IP rating determines the degree of protection to dust and liquid. Typically, medical connectors are rated IP54 and above, with many being IP67 for temporary immersion in liquid.

Screw connectors provide the ultimate protection against accidental un-mating and have excellent IP performance but, on the downside, they are generally the most expensive, especially the metal versions.

Push-pull connectors can be expensive. However, plastic versions have reduced costs and provide quick mating and IP67 protection, with some protection against accidental un-mating.

Snap-in and bayonet connectors provide quick and simple mating and are generally the cheapest. Recent developments mean that these can now be rated to IP67 thus providing economic yet high-performance solution.

New mating systems such as those from Binder, such as the innovative Easy Locking Connector (ELC) (Figure 1), provide positive mating and protection against accidental un-mating with a unique intuitive locking system featuring snap hooks. Here, the friction-free connection allows over 5000 mating cycles.

The new Binder ELC series 570 connector features a PA66 plastic housing, has 12 gold-plated contacts for 0.25mm² wires and is rated at 2A, 150V.

The female panel mount connector provides protection against the ingress of liquids, water splash and accidental electrical contact and, when mated, the new easy-locking connector offers protection to IP54.

Sterilisation and cytotoxicity

Medical applications are wide ranging, with surgical applications requiring connectors resistant to medical sterilisation via steam autoclave, gamma radiation and gas plasma, etc. However, some applications require no sterilisation whilst others require specific material, tested for cytotoxicity (toxicity to skin) and free from DEHP phthalates.

Standards

There are several standards that should be considered when specifying connectors. EN 60601 is a family of standards with scope that covers safety, essential performance and electromagnetic compatibility of medical electrical equipment and systems. It is technically equivalent to the international standard IEC 60601, and covers aspects such as vibration, shock, rough handling and finger-proofing.

ISO 13485 specifies requirements for a quality management system where an organisation must demonstrate ability to provide medical devices and related services that consistently meet customer and applicable regulatory requirements.

The US Food & Drug Administration (FDA) continues to promote the development of connectors that reduce the risk of device misconnections. These standards promote patient safety by assuring connectors for unrelated systems are incompatible, so the devices cannot be accidentally linked or forced to fit.

Made to measure

Some applications require a hybrid connector to carry gas in addition to power and signal, and in such cases the best solution may be a bespoke connector. This not only provides the optimum solution but also gives the customer protection of its own intellectual property. Naturally, medical connectors tend to be expensive – but a price can’t be placed on patient safety. Binder offers technical and commercial assistance when it comes to specifying the right connector for medical applications.

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