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THE UNIVERSITY OF NEW SOUTH WALES

School of Electrical Engineering and Telecommunications

ELEC4623 / 9734 : BIOMEDICAL INSTRUMENTATION, MEASUREMENT AND DESIGN

LABORATORY 4

Electrical Safety Testing of Biomedical Equipment

AS3003 Electrical Installation – Patient Treatment Areas of Hospitals and Medical and Dental Practices

AS3200.1.0 Approval and Test Specification for Medical Electrical Equipment – General Requirements for Safety – Parent Standard.

AS3551 Acceptance Testing and In-service Testing – Electro-Medical Equipment.

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BACKGROUND

This laboratory will make heavy use of the ELEC-1DA AS/NZS3551 Electrical Safety Tester from medical Equipment Management Australasia and students are advised that they MUST read these laboratory notes in conjunction with the Operators Manual before attempting any part of the experiment.

As some of the tests apply high voltages to the equipment provided, the Laboratory demonstrators MUST check the equipment connections BEFORE the test is carried out. The tests that can be performed are described on See Page 4 and 5 of the operator manual. They are;

BASIC TESTS RANGE

Mains Supply Polarity 0-280V

Steady State Load Current 0-10.0 A

Peak Load Current 0-25.0 A

Ground Wire Resistance 0-1.999Ω

Insulation Resistance

Active and Neutral to Earth 0-199.9MΩ

Active and Neutral to Socket 0-199.9MΩ

Earth to Socket 0-199.9MΩ

Earth Leakage Current

Mains Supply Normal 0-1.999mA

Mains Supply Neutral Open 0-1.999mA

4-Wire Resistance 0-1999mΩ

Millivolt Potential 0-1999mV

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METHODS

(1) Using the ELEC-1 module (3.1.1 – 3.1.8)

Carry out Equipment Pre-test on the Electrical Safety Tester 3.1.1

Carry out the following basic tests (3.1.2 - 3.1.8) on the following equipment

a.) Isolation transformer b.) Electric Fan c.) Personal Computer (with WIN-ECG card included) d.) Electric Fan connected to isolation transformer e.) Personal Computer connected to isolation transformer

Earth Conductor Resistance Test (Protective earthing tests) 3.1.2 (Fig 5.1a)

Earth Conductor Resistance Test – Extension Leads 3.1.3 (Fig 5.1b&c)

Insulation Resistance Test 3.1.4 (Fig 5.2)

Earth Leakage Current Test 3.1.5 (Fig 5.3)

Load Current 3.1.6

Inrush Current 3.1.7

Other Insulation Resistance Tests 3.1.8

• Active/Neutral to Output Socket

• Earth to output Socket

Note:

• R Earth is equivalent to R Gnd W

• In 3.1.2, a good contact point to test the protective earthing for the fan and the isolation transformer would be the metal screw, and for the computer it would be the metal plate at the back.

• In 3.1.3, connect one end of the extension cord to the test socket and another end to the black sockets via the earth-to-2-pin adaptor

(2) Using the APP CCT-2 module (3.2.1 – 3.2.2)

Tests to be carried out ONLY on;

• Personal Computer (with WIN-ECG card included)

• Personal Computer and Isolation Transformer

Applied Part Current Test (API) 3.2.1 (Fig 5.4)

• API/ With power conductors connected normally

• API/NO With Neutral Conductor open circuited

• API/EO With Earth open circuited

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Mains Contact Current Test (MCI) 3.2.2 (Fig 5.5)

• MCI/BF Body Floating Input Circuits.

• MCI/CF Cardiac Floating Input Circuits

Note:

• This test can only be applied to BF and CF rated circuits

• Connect the 12-lead ECG to the corresponding slots in APP CCT-2 (L = LA, R = RA, F = LL, N = RL, V1 = C1 etc)

WARNING: This test provides dangerous potentials on the applied parts (Patient leads).

DO NOT TOUCH THESE TERMINALS DURING THE TEST!!!

(3) TESTING TO AS3003 – “Electrical Installation – Patient Treatment Areas of Hospitals and Dental Practices” using the DISP-3 module (3.3.1 – 3.3.2)

Connect test leads to MEM DISP-3 Module 3.3

Perform a 4-Wire resistance test 3.3.1

Perform a millivolt Potential Test 3.3.2

Note:

• For this test, connect 3 pin plug adapters to one end of the long leads, another end to the sockets on the DISP-1 unit (one lead to the Red Input sense/Constant current and another lead to the Black Input sense/Constant current).

• Plug one lead to a power point in you immediate vicinity and another lead to a power point at some distance apart in order to measure the resistance and potential between the 2 power points.

LABORATORY REPORT

In your report, describe the purpose of each test and the outcomes of the test. Decide whether the various pieces of equipment tested (Fan, PC+WIN-ECG with and without isolation transformer etc.) comply with the AS3200.1.0 standards.

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ELECTRICAL SAFETY TESTING TO THE NEW AUSTRALIAN AND NEW ZEALAND STANDARD AS/NZS 3551:1996 TITLED “TECHNICAL MANAGEMENT PROGRMS FOR MEDICAL DEVICES.”

A paper delivered by the IEAust Biomedical Engineering College Seminar, 19th September 1996.

Introduction to Australian Electro-Medical Standard.

Australian standards have always been at the forefront of technology and Standards Australia have produced a range of Electro-medical Standards.

AS3003 “Electrical Installation – Patent Treatment Areas of Hospitals and Medical and Dental Practices”.

This is a ‘wiring’ standard designed to prevent micro-electrocution and macro-electrocution during sophisticated medical procedures. AS3003 was first published in 1976.

AS3200.1.0 “Approval and Test Specification for Medical Electrical Equipment – General requirements for Safety – Parent Standard.

This is a series of standards for electro-medical equipment design and manufacture and is directly related to the IEC 601.1 series of standards. AS3200 was first published in 1986.

AS2500 “Guide to the Safe Use of Electricity in Patient Care”.

This standard was produced for Hospital Administrators, Medical and Para Medical personnel to explain the risks using some items of electro-medical equipment and performing certain medical procedures. A video is also available from Standards Australia. This standard was first published in 1982.

AS3511. This standard was originally titled “Acceptance Testing and In-service Testing – Electro-Medical Equipment.”

It was first published in 1988.

Images in this document are reproduced with permission from Standards Australia. Standards Australia are on the web at http://www.standards.com.au/~sicsaa/

Comparison between AS3551 and the new AS/NZS3551:1996. With the electro-medical standards in place, Australia has achieved an outstanding electrical safety record for many years. The new 3551 jointly prepared and standardised with New Zealand, places far more emphasis on performance testing and maintenance of electro-medical equipment. Due to the vast experience with electrical safety testing, some of the tests have been omitted or simplified in the new 3551.

AS/NZS3551:1996 Electrical Safety Testing Paper.

In order to simplify the description of testing procedures, I have divided the equipment into two categories.

A. Electromedical equipment without applied parts. (Applied parts is the new terminology for patients circuits)

B. Electromedical equipment with applied parts.

A. Electro-Medical Equipment without applied parts.

Only four electrical safety tests are required for Class 1 equipment.

1.Protective Earthing Tests

2.Insulation Resistance Test

3(a) Earth leakage-All supply conductors.

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3(b) Earth leakage-Neutral open.

1. Protective Earthing Test.

Protective earthing tests ensure that in the case of a breakdown of mains carrying parts, the fuse or circuit breaker in the device or supply will operate to clear the fault.

Figure 5.1a illustrates the test for a fixed wired mains lead. Earth resistance sometimes referred to as ground wire resistance should not exceed 0.2 ohms.

Note 5.1a also gives specifications for the test instrument and states that a current-operated method rather than a multimeter is required for New Zealand.

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Figure 5.1b illustrates equipment with a detachable power supply cord. The total resistance allowed is now 0.3 ohms with 0.2 ohm for the cord and 0.1 ohm around the medical equipment.

Figure 5.1c and d illustrates the separate measurements.

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Working with detachable power cords and high power equipment.

The resistance allowable by the earth conductor is a maximum of 0.2 ohm. If the earth conductor is 0.2 ohm, then it stands to reason that the current carrying conductors may also be at 0.2 ohms.

For large powered equipment for example using 10 amps, then we have

P = 1 x 1 x R

= 10 x 10 x 0.2

= 20 Watts.

This power could be dissipated across the entire cable or at one or both ends. This also explains why melting has occurred at the IEC socket ends on some equipment.

Additional Ground Paths.

Equipment tested on a bench in a laboratory would not present additional ground paths that could be found, for example, in an Intensive Care Unit. Equipment in an ICU may be grounded via mounting brackets, supplementary earth cables for Cardiac procedures or central station wiring in addition to the earth of the power supply cord.

Ensure that your test instrument, if mains powered, has its test leads isolated from the supply ground to avoid parallel paths and measurement errors.

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2. Insulation Resistance Test.

Insulation Resistance Testing provides a non-destructive DC voltage check of the mains carrying part of the equipment. It is not a test requirement of AS3200.1 or IEC601 but experience has shown that IR testing can and does pickup faults and therefore should remain as part of the testing regime.

The experience of the writer and colleagues has shown the following faults detected with IR testing.

(a) A neutral ground short on equipment brought into the hospital.

(b) Carbon tracking on an ECG input board that had been subjected to many defibrillator applications.

(c) The wrong rubber compound used on a strain relief section of an intra cardiac signal lead. (the rubber was conductive between external surfaces and intra cardiac catheter connections.

Figure 5.2 illustrates the tests required, the characteristic of the IR meter, the test conditions and the test specifications.

Note: The IR meter should provide 500V +/- 50v DC into 10M ohms. This can be easily tested as most digital multimeters have an input impedance of 10M Ohms on the DC volts range.

Note: Most test equipment, even those supposedly designed for medical testing, FAIL THESE REQUIREMENTS. The IR meter requirements are the same as listed in the 1988 version of the standard.

MEASURING DEVICE:-

In order to standardise on current measurements for the remaining electrical safety tests, AS 3551, AS 3003 and AS/NZS 3551 use the measuring device shown in Figure A1.

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APPENDIX A

MEASURING DEVICE

(Normative)

Diagram A1 below, details the basic requirements for a measuring device, which would meet the requirements of this Standard. The device shall measure RMS values including d.c.

Figure A1 illustrates the components used in conjunction with a true RMS meter – DC coupled. A 1 Kilohertz roll off response is achieved with the measuring device.

NOTE: Most test equipment, even those supposedly designed for medical testing FAIL THESE REQUIREMENTS

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3. Earth Leakage:-

This measuring device is placed in the earth return line of the equipment undertest and gives an indication of the health of the mains carrying parts when the equipment is switched on in its operating mode.

The first test does not open the supply conductors, but the second test opens the neutral conductor. For this reason, it is very important to ensure the polarity of the mains source, so that in the second test, the active, or hot wire is still presented to the equipment under test. The test equipment may have a polarity test and this should be verified before applying these tests.

3(a) and 3(b). Earth leakage tests are illustrated in figure 5.3. You will not the MD (measuring device) in the earth return and switch S1 will open the neutral conductor. Table 5.1 lists the maximum levels permitted.

WARNING: As previously mentioned, equipment in ICU’s etc. may have additional ground paths that will not allow leakage current to flow via the MD. A two meter power cable has 18μA leakage, so if the meter reads zero, the meter is faulty or another ground path exists. If the power cable is detachable, remove it from the equipment and check the reading.

It is possible to do a worst case (3b) test without disconnecting all of the additional earths by using the Mains Contact Current test – test No 5 as discussed, with equipment that has applied parts. After this test has been described the pseudo earth leakage test will be discussed.

EQUIPMENT WITH APPLIED PARTS

Tests 1,2,3(a) and 3(b) are performed first then testing is continued with tests 4(a), 4(b), 4(c) and 5.

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4. Applied Part Leakage Current.

It is important to understand that with this test we are seeing what current can come from the applied parts when we interrupt supply conductors. Alternatively it can be said that we are looking at current SOURCED from the test item.

The measuring device has now been placed between the applied parts and ground. Figure 5.4 shows the test set up, describes the test conditions and gives maximum levels.

The maximum levels apply separately with applied parts ratings of CF, BF and B. All applied parts are shorted together for these tests.

4(a) All supply conductors are presented to the equipment under test.

4(b) The neutral conductor is interrupted.

4(c)The earth conductor is interrupted.

5. MAINS CONTACT CURRENT

WARNING: This test provides dangerous potentials on the applied parts connections. It should only be done by trained personnel and should NOT be applied to Type B Applied Parts.

This test applies the same voltage as the normal mains supply into the applied parts. The MD is now positioned between ground and one end of the small isolating transformer.

If the applied parts have a rating of BF, all applied parts are shorted together and the maximum 5mA applies.

If the applied parts have a rating of CF, all applied parts are tested individually and a maximum of 50μA applied to each applied part.

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Figure 5.5 illustrates the test set-up, provides details of its transformer requirement, the test conditions and specifications.

NOTE: The transformer requirements are that 5mA can be sourced with a regulation of 5%. Therefore with a 240 volt supply, Output Voltage Open Circuit should not exceed 252V and with a 5mA load (48k for 240V), the Output Voltage should not fall below 228V.

NOTE: Most test equipment, even those supposedly designed for medical testing, FAIL THESE REQUIREMENTS.

HANDY TIP. The standards committee is aware of the time it would take to complete a MCI-CF test for say a diagnostic ECG machine with 10 applied parts. They offer the following: - Even though the applied parts are rated as CF, do a BF MCI test an if the level is equal to or lower than 50μA, individual CF testing is not required.

APPLIED PARTS OTHER THAN ECG.

ECG applied parts are the easiest to test as you can make direct connections between the test instrument and the leads themselves, But what about testing other inputs such as Invasive Pressure, Sa02, ETC02, Temperature, Cardiac Output, etc.

My recommendation is to wrap the transducers in aluminium foil and apply the Applied part leakage current and Mains contact current tests.

The tests should be performed when acceptance testing the equipment and at regular intervals during the life of the transducers at intervals related to their wear and tear.

PSEUDO EARTH LEAKAGE CURRENT TEST

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The MEM Figure shows the Mains Contact Current Test, set on the BF range applied to the active pin of the equipment power cord.

The instrument under test has multiple earth connections and therefore the conventional earth leakage test set up will not provide accurate readings.

The pseudo earth leakage current test will give an approximation of the worst case – neutral open earth leakage current without the need to disconnect all of the earths.

KEVIN E. O’BRIEN

Assoc. IEAust. FSEA

Medical Equipment Management Australasia Pty Ltd.

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