Powering patient-connected equipment

May 22, 2017

GaryBocock-May 22, 2017

This paper discusses two approaches for power systems within medical equipment for patient-connected applications. The part of the equipment that comes into contact with the patient is known as the ‘applied part’. The applied part is defined as the part of a medical device which, to enable the overall device to perform its function, deliberately comes into direct contact with a patient. This also applies to parts likely to come into contact with the patient.

Applied parts are classified in the 60601-1 suite of standards, according to the type of patient contact and the type or nature of the medical device. The latest version of 60601-1 is the third edition, first published in December 2005. The standard has been adopted in the major countries and regions of the world and published as the following latest versions:

IEC 60601-1:2005 (Third Edition) + CORR. 1:2006 + CORR. 2:2007 + A1:2012

Europe: EN 60601-1:2006/A1:2013/A12:2014

USA: ANSI/AAMI ES60601-1: A1:2012, C1:2009/(R)2012 and A2:2010/(R)2012

Canada: CSA CAN/CSA-C22.2 No. 60601-1:14

Each classification has differing requirements for protection against electric shock. The classifications are outlined below, from the least to the most stringent:

Type B (Body). Type-B classification is given to applied parts that are generally not conductive and may be connected to Earth.

Type BF (Body Floating). Type-BF classification is given to applied parts that are electrically connected to the patient and must be floating and separated from Earth. This classification does not include applied parts that are in direct contact with the heart. 

Type CF (Cardiac Floating). Type-CF classification is given to applied parts suitable for direct cardiac connection (connection to the heart of the patient, including intravenous). These parts must be floating and separated from Earth.

Power systems for type-BF and type-CF medical devices are designed to provide additional isolation from the secondary output to Earth, normally rated at 1 x means of patient protection (MOPP) at the AC line voltage.

Insulation test voltages based on 250 VAC working voltage. 
MOP = Means of protection
MOOP = Means of operation protection
MOPP = Means of patient protection

Additionally, these power systems must limit the Earth leakage current, enclosure leakage current and particularly the patient leakage current, as defined in the table below.

NC = Normal conditions

SFC = Single-fault conditions 
*Patient care equipment maximum Earth and enclosure leakage current for the USA is 300 μA 
Figures quoted are for portable equipment.

Earth leakage current = Current flowing in the Earth conductor
Enclosure leakage current = Current flowing to Earth via the patient from the enclosure 
Patient leakage current = Current flowing to Earth via the patient from an applied part 
Patient auxiliary current = Current flowing between two applied parts

Continue to page two on Embedded's sister site, EDN: "Product how to: Power systems for Patient-Connected equipment."

 

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