What is a Medical Isolation Transformer or MIT?
In the ever-evolving realm of medical technology, electrical equipment plays a critical role in patient diagnosis, treatment, and monitoring. Undeniably, these innovative devices have revolutionized the healthcare industry; procedures and diagnostic functions like tomography, ECG, endoscopy, and even most dental treatments would be impossible without electricity.
However, it is imperative to acknowledge that along with their countless benefits comes the potential for certain risks. Electrical hazards within medical settings can pose a significant threat to patients and dedicated healthcare professionals.
Medical systems must safely comply with the Medical Leakage currents required by IEC/EN60601, the European harmonized standard to meet the Medical Device Directive. These are categorized as
- Earth leakage current is where current flows from the Live Conductor to the PE connection.
- Patient leakage current, where current flows to the patient via probes and other instruments known as Applied Parts
- Touch current is current that flows from the equipment enclosure or parts of it through an external path (not PE) to Earth.
Earth leakage currents must be limited in Medical Devices to less than 100 microamps under normal conditions, and a Medical Isolation Transformer is a key part of achieving this.
An MIT works by providing electrical isolation between the primary and secondary connections and, importantly, disconnecting the neutral conductor from the Protective Earth, effectively limiting the leakage current to parasitic elements and providing power to the connected Medical Equipment, which is both inherently safer and allows conformity to be more easily achieved.
It's important to know that to comply with IEC/EN60601, the units must be tested for isolation resistance to 4k V. In contrast, standard commercial or domestic application isolation must be tested only to 2.5 kV.
While MITs are usually manufactured using toroidal transformers, resulting in reduced magnetic stray fields and increased electrical efficiency, it is essential to understand that Medical Isolation Transformers are not Medical Devices, but by specifying one that is manufactured and tested to the pertinent elements of IEC/EN60601, product compliance for the completed equipment will be much more straightforward.
Medical Isolation Transformers can often be supplied with electronic switch-on current limiting, which reduces unwanted tripping and fuse blowing, overvoltage protection to increase resilience, and an EMI line filter to ensure compliance with EMC standards for emissions and immunity.
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