Ecg Lead Leakage

Many ESAs incorporate ECG lead connections,so that the ECG leads of monitor and other such devices may be tested for leakage.Just asthere are specifications for chasis orcase leakage current,Ecg leads also have maximum leakage current values assigned.

Most lead equip ESAs will have either 5 or 10 lead connections.To the uninitiated,this can be confusing and intimidating array of connections.Risk current may be available on the DUT from one of the insulated leads to ground,or from the one to another.Either situation poses a shock hazard.Therefore,most ESAs are set up to check either "lead to ground" or "lead to lead".

Ground Wire Resistance

The ground wire resistance is a crucial part of the measurement.First,it is assumed that all electrical receptacles in the patient room are tied together to a known good earth ground.The receptacles are tested after installation and generally at regular intervals thereafter.Since a good earth ground is available in the room,all line connected devices must be referenced (connected) to this same ground to help avoid shock hazard.This connection is achieved via the ground conductor in the power cord of each device.The generally accepted maximun value for ground wire resistance is 0.5 ohms.

Leakage current - The Main Ingredient of Safety Testing

The primary component - the bottom line,if you will..is the amount of microshock current that would flow through a patient who comes in contact with the DUT (Device Under Test).The ESA simulates the patient and indicates the amountof leakage current the patient would receive if someone was exposed to the DUT.

History of Electrical Safety Analyzers

The basic tool of the trade is a piece of test equipment called an Electrical Safety Analyzer.for brevity the abbreviation "ESA" shall be used for reminder of this course.The ESA dates back to the 1960s.It is generally accepted that the first ESA came to be when a hospital in Alaska,who had become aware of the needto perfom this testing,contacted Dr Norman Alpert at a University in Chicago.Dr. Alpert build and designed a very basic analog unit for the Alaskan hospital.Later, after moving to the Burlington,Vermont area,Dr. Alpert and george Luhr formed Bio-Tek Instruments.

A company dedicated to the manufacture and marketing of specialized test devises for medical equipment.Mr. Luhr left the firm but Dr. Alpert remains the company pesident.Neurodyne Demspey (now called Dynatech Nevada),Instrutek,Bio-Design and others all tried their hands and opportunity in the market.Most of these firm have gone out of business but Bio-Tek ang Dynatech Nevada continue to thrive and dominant manufacturers of ESAs today.


Primary Functions

There are two primary functions associated with an ESA.

1- Leakage current measurement

2- Measurement of the resistance of the ground conductor in the power cord of the DUT
(Device Under Test)