Medical Electronics
equipment with physical contact to patients, the requirements for products need to be stricter. In the hypothetical case of an earth fault, the current could flow through a patient touching the device. For sensitive applications as syringe pumps, medical ventilators, lasers or patient monitoring devices, the maximum permissible leakage current is therefore limited to 0.1 mA AC in normal operation. In the single fault condition, where, for example, one line of the mains connector is disconnected, 0.5 mA AC is permissible. This limit is considered as safe level for the greatest risk, which is ventricular fibrillation in the heart of the patient.
Overview MOP Classifications
1 x MOOP 2 x MOOP 1 x MOPP
2 x MOPP
www.cieonline.co.uk
To reduce this risk, EMC engineers often apply “medical” EMC filters which have no capacitors from live to protected earth. (e.g., Schaffner FN9262xB..). These filters do not add leakage current towards protected earth to the equipment and therefore facilitate compliance to IEC EN 60601-1. The simplest version has only one capacitor between live (P) and neutral (N). In non-medical EMC filters, capacitors (not in the picture) would mitigate EMI between live (P)/ neutral (N) towards protected earth. In a medical grade EMC filter without a Y-capacitor, this so-called common mode functionality is provided by the common mode inductor, marked “2x L1” in the picture left.
The Means of Protection (MOP) safety classification in IEC60601-1 Safety requirements in IEC60601-1 define two categories of product safety. Means of Patient Protection (MOPP) and Means of Operator Protection (MOOP). Each of these categories are subdivided in values for basic or double insulation. Choosing between MOPP and MOOP seems straightforward. Medical electrical equipment which does not come in contact with patients can be rated with the lower requirements of operator safety: MOOP. This saves time in costs in the certification, but needs certainty, that no patient can come in contact unintentionally.
FN9274
Isolation 1.500 VAC
3.000 VAC 1.500 VAC
4.000 Vac
Creepage / Clearance 2.5 mm / 2 mm
5 mm / 4 mm 4 mm / 2.5 mm
8 mm / 5 mm
Insulation Basic
Double Basic
Double
The standard also specifies situations, where more than one MOP is required, in case either one fails. Now, double insulation needs to be applied. All parts of the medical electrical equipment need to be reviewed for their MOP level. “Medical” EMC filters typically provide the value in the datasheet. Some filters even comply to the highest rating (2 x MOPP) without any additional insulation measures (e.g., Schaffner FN9274).
www.schaffner.com Components in Electronics December/January 2022 17
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