Choosing transformers for critical medicine
Modern examination and operating methods would not be possible without the use of electricity. Transformers used in these applications are designed to protect patients, staff and the equipment used in their care, and as such are required to meet demanding specifications. Steve Hughes, Managing Director at REO UK, explains the key considerations when specifying a medical transformer.
Medical requirements for the design of electronic systems can generally be considered among the most rigorous. Because these standards, such as the IEC 60601-1 and the EU guideline 93/42/EWG, are especially demanding of products that will be used on or by patients whose health is already compromised, virtually all components of medical electronic products, as well as the end products themselves, must be designed with safety in mind.
There are lots of key considerations when specifying a transformer for medical applications. For example, there are several types of insulation system temperature ratings for transformers, used for determining the overload capability and life expectancy. The insulation system is the highest internal temperature that a transformer can withstand, with a life expectancy of around 20-25 years when working within the limits.
The IEC60601-1 standard requires medical transformers to pass a high potential (HIPOT) test – a stress test of the insulation of a device beyond what it would encounter during normal use. Medical equipment with applied parts that have direct contact with a patient is tested at much higher parameters than the norm, testing at 4,000V.
The test also determines what will happen when a series of secondaries are shorted out, with one of two possibilities. The transformer will either heat up and catch fire, or if there is an internal thermal fuse present, cease to function. If the transformer does not perform acceptably, it and the equipment in which it is housed fails the test.
Leakage current is one of the most important specifications for medical grade transformers. Medical systems must safely meet the leakage current requirement specified – if several devices are switched together, the overall leakage current increases accordingly. Isolating transformers, such as the TÜV-certified REOMED products, are proven and reliable equipment, limiting the leakage current and thus helping to ensure patient and staff safety.
REOMED isolation transformers are characterised by their high level of safety and very low magnetic stray field, whilst also providing high efficiency and easy connectivity. In addition to the standard range, custom transformers can be enhanced by adding an electronic starting current limiter, surge protector and mains filter.
While the requirements of medical electronic systems are rigorous, working with the transformer manufacturer can set design engineers on the best path to fulfilling these standards. REO, and its REOMED product range, draws on years of tradition in the production of transformers, and offers solutions which go above and beyond the high standards set.