Calibration and Electrical Safety of Medical Equipment

1. Calibration and Electrical Safety of Medical Equipment Dr Fadhl Al-Akwaa fadlwork@gmail.com www.Fadhl-alakwa.weebly.com

2. Why Test & Calibration What you cannot measure you cannot control

3. As components age and equipment undergoeschanges in temperature or humidity or sustainsmechanical stress, performance graduallydegrades. This is called drift. When this happens your test results become unreliable and both design and performance quality suffer. While drift cannot be eliminated, it can be detected and either corrected or compensated for through the process of calibration.

4. • Calibration: process of comparing an unknown against a reference standard within defined limits, accuracies and Uncertainties • Verification: process of comparing an unknown against a reference standard at usually one data point Definitions

5. – Written Program – Routine calibration or verification at suitable intervals – Control of inspection, measuring and test equipment. – Calibration procedures including specific directions and limits for accuracy and precision – Deviation or discrepancies should be investigated – Traceable Calibration Standards – Calibration records – Visible Calibration status Requirements of Test & Calibration service

6. • Performance Testing • Safety Testing What to TEST for?

7. When to test • On newly acquired equipment prior to being accepted for use • During routine planned preventative maintenance. • After repairs have been carried out on equipment.

8. Need for Medical Equipment Testing • Medical device incidents resulting in patient injury and death• Ensure that the equipment is performing to the expected standards of accuracy, reliability, free of hysteresis and linear (as designed).• Safe and effective devices need to be available forpatient care– Downtime costs money• Regulations, accreditation requirements and standards.

9. Why do we do electrical safety? • Ensure patient safety • Protect against macroshock • Protect against microshock • Test for electrical internal breakdown / damage to power cord, AC mains feed, etc. • Meet codes & standards • AAMI, IEC, UL, NFPA, etc. • Protect against legal liability • In case of a patient incident

10. International Electrotechnical Commission • The International Electrotechnical Commission[1] (IEC) is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology".

11. International Electrotechnical Commission • IEC standards cover a vast range of technologies from power generation, transmission and distribution to home appliances and office equipment, semiconductors, fibre optics, batteries, solar energy, nanotechnology and marine energy as well as many others. • The IEC also manages three global conformity assessment systems that certify whether equipment, system or components conform to its International Standards.

12. International Electrotechnical Commission • Today, the IEC is the world's leading international organization in its field, and its standards are adopted as national standards by its members. The work is done by some 10 000 electrical and electronics experts from industry, government, academia, test labs and others with an interest in the subject. • They also first proposed a system of standards, the Giorgi System, which ultimately became the SI, or Système International d’unités (in English, the International System of Units).

13. IEC, ISO, ITU, IEEE • The IEC cooperates closely with the International Organization for Standardization (ISO) and the International Telecommunication Union (ITU). In addition, it works with several major standards development organizations, including the IEEE with which it signed a cooperation agreement in 2002, which was amended in 2008 to include joint development work. • Other standards developed in cooperation between IEC and ISO are assigned numbers in the 80000 series, such as IEC 82045-1.

14. List of IEC standards • IEC standards have numbers in the range 60000–79999 and their titles take a form such as IEC 60417: Graphical symbols for use on equipment. The numbers of older IEC standards were converted in 1997 by adding 60000, for example IEC 27 became IEC 60027.

15. List of IEC standards • IEC 60027 Letter symbols to be used in electrical technology... • IEC 60034 Rotating electrical machinery • IEC 60038 IEC Standard Voltages • IEC 60044 Instrument transformers • IEC 60050 International Electrotechnical Vocabulary • IEC 60062 Marking codes for resistors and capacitors • IEC 60063Preferred number series for resistors and capacitors • IEC 60065 Audio, video and similar electronic apparatus - Safety requirements • IEC 60068 Environmental Testing • IEC 60071 Insulation Co-ordination • IEC 60073 Basic Safety principles for man-machine interface, marking and identification http://en.wikipedia.org/wiki/List_of_IEC_standards

16. List of IEC standards • IEC 60601 Medical Electrical Equipment • IEC 62304 Medical Device Software - Software Life Cycle Processes • IEC 62366 Medical devices—Application of usability engineering to medical devices • IEC 62464 Magnetic resonance equipment for medical imaging http://en.wikipedia.org/wiki/List_of_IEC_standards

17. IEC 60601-x-xx • – the IEC 60601-1-xx series of collateral standards for MEDICAL ELECTRICAL EQUIPMENT; • – the IEC 60601-2-xx series of particular standards for particular types of MEDICAL • ELECTRICAL EQUIPMENT; and • – the IEC 60601-3-xx series of performance standards for particular types of MEDICAL ELECTRICAL EQUIPMENT.

18. IEC 60601-x-xx • IEC 60601-1-2, Medical electrical equipment – Part 1-2: General requirements for safety Collateral standard: Electromagnetic compatibility – Requirements and tests • IEC 60601-1-3, Medical electrical equipment – Part 1: General requirements for safety – 3. Collateral standard: General requirements for radiation protection in diagnostic X-ray equipment

19. IEC 60601-x-xx • IEC 60601-1-6, Medical electrical equipment – Part 1-6: General requirements for safety Collateral standard: Usability • IEC 60601-1-8, Medical electrical equipment – Part 1-8: General requirements for safety Collateral standard: General requirements, tests and guidance for alarm systems in medical electrical equipment and medical electrical systems

21. Physiological Effects of Electricity The human body can easily detect macroshock and violent reactions occur to high current flow level in the body… Below 1 ma (1,000 µa), it is often much more difficult to detect the presence of a shock hazard from simple perception…

22. Classes and types of medical electrical equipment • Equipment Class{I,II,III} method of protection against electric shock • Equipment Type{B,BF,CF} degree of protection

23. Classes and types of medical electrical equipment • All electrical equipment is categorised into classes according to the method of protection against electric shock that is used. For mains powered electrical equipment there are usually two levels of protection used, called "basic" and "supplementary" protection. The supplementary protection is intended to come into play in the event of failure of the basic protection.

24. Class I • Class I equipment has a protective earth. The basic means of protection is the insulation between live parts and exposed conductive parts such as the metal enclosure. • In the event of a fault that would otherwise cause an exposed conductive part to become live, the supplementary protection (i.e. the protective earth) comes into effect. A large fault current flows from the mains part to earth via the protective earth conductor, which causes a protective device (usually a fuse) in the mains circuit to disconnect the equipment from the supply.

25. Class I

26. Class I • term referring to electrical equipment in which protection against electric shock does not rely on BASIC INSULATION only, but which includes an additional safety precaution in that means are provided for ACCESSIBLE PARTS of metal or internal parts of metal to be PROTECTIVELY EARTHED

27. CLASS II • term referring to electrical equipment in which protection against electric shock does not rely on BASIC INSULATION only, but in which additional safety precautions such as DOUBLE INSULATION or REINFORCED INSULATION are provided, there being no provision for protective earthing or reliance upon installation conditions

28. Class II

29. Class III equipment • Class III equipment is defined in some equipment standards as that in which protection against electric shock relies on the fact that no voltages higher than safety extra low voltage (SELV) are present. SELV is defined in turn in the relevant standard as a voltage not exceeding 25V ac or 60V dc. In practice such equipment is either battery operated or supplied by a SELV transformer.

30. If battery operated equipment is capable of being operated when connected to the mains (for example, for battery charging) then it must be safety tested as either class I or class II equipment. Similarly, equipment powered from a SELV transformer should be tested in conjunction with the transformer as class I or class II equipment as appropriate. • It is interesting to note that the current IEC standards relating to safety of medical electrical equipment do not recognise Class III equipment since limitation of voltage is not deemed sufficient to ensure safety of the patient. All medical electrical equipment that is capable of mains connection must be classified as class I or class II. Medical electrical equipment having no mains connection is simply referred to as "internally powered".

31. Equipments Type different pieces of medical electrical equipment {APPLIED PARTS} have different areas of application and therefore different electrical safety requirements. For example, it would not be necessary to make a particular piece medical electrical equipment safe enough for direct cardiac connection if there is no possibility of this situation arising.

32. Normative Reference Page 371 • Current density and electrically induced ventricular fibrillation. Medical Instrumentation, January-February 1973, Vol. 7, No. 1. • WATSON, AB. and WRIGHT, JS., Electrical thresholds for ventricular fibrillation in man. Medical Journal of Australia, June 16, 1973.

33. Terminology and definitions • http://www.601help.com/Disclaimer/glossary.html#ProtectiveEarthTerminal

34. Terminology and definitions • L1 Hot • L2 Neutral • Earth Ground • Mains Line Voltage • Applied Parts Patient Leads • Enclosure/Case Chassis • Protective Earth Ground Wire • Earth Leakage Current Leakage in Ground Wire

35. Terminology and definitions • Enclosure Leakage Chassis Leakage • Patient Leakage Lead Leakage • Patient Auxiliary Leakage between Patient Leads • Mains on Applied Parts Lead Isolation • Insulation Resistance Dielectric Strength or Insulation Resistance between Hot and Neutral to Ground • Earth Resistance Ground Wire Resistance

36. R.M.S and Peak to Peak Vrms is the value indicated by the vast majority of AC voltmeters. The RMS value of an alternating voltage or current is the same as the level of direct voltage or current that would be needed to produce the same effect in an equal load. For example, 1 V applied across a 1 Ω resistor produces 1 W of heat. A 1 Vrms square wave applied across a 1 Ω resistor also produces 1 W of heat. That 1 Vrms square wave has a peak voltage of 1 V, and a peak-to-peak voltage of 2 V.

37. Calculate RMS ≈ 0.707 Vpk

38. RMS is a sort of average and peak is the top level • A peak is an instant reading - RMS is an "average" reading. RMS means to take the root of the mean and square it. • RMS value is the DC equivalent value to an AC stream. • The RMS value of an alternating voltage or current is the same as the level of direct voltage or current that would be needed to produce the same effect in an equal load.

39. Crest Factor • The Crest Factor is equal to the peak amplitude of a waveform divided by the RMS value. • Electrical engineering — for describing the quality of an AC power waveform

41. Applied Part No applied part table Parts that contact PATIENTS Applied Part A part of the equipment which in normal use: necessarily comes into physical contact with the patient for the equipment to perform its function; or can be brought into contact with the patient; or needs to be touched by the patient

42. Accessible Part • Part of equipment which can be touched without the use of a tool. • EXAMPLE 1 Illuminated push-buttons • EXAMPLE 2 Indicator lamps • EXAMPLE 3 Recorder pens • EXAMPLE 4 Parts of plug-in modules • EXAMPLE 5 Batteries

43. Leakage currents • Current that is not functional. • several different leakage currents are defined according to the paths that the currents take. • Earth Leakage Current • Enclosure Leakage Current • Patient Leakage Current • Patient auxiliary current

44. Causes of Leakage currents • If any conductor is raised to a potential above that of earth, some current is bound to flow from that conductor to earth. • The amount of current that flows depends on: 1- the voltage on the conductor. 2- the capacitive reactance between the conductor and earth. 3-the resistance between the conductor and earth.

46. EARTH LEAKAGE CURRENT • current flowing from the MAINS PART through or across the insulation into the PROTECTIVE EARTH CONDUCTOR

47. EARTH LEAKAGE CURRENT • Under normal conditions, a person who is in contact with the earthed metal enclosure of the equipment and with another earthed object would suffer no adverse effects even if a fairly large earth leakage current were to flow. This is because the impedance to earth from the enclosure is much lower through the protective earth conductor than it is through the person. However, if the protective earth conductor becomes open circuited, then the situation changes. Now, if the impedance between the transformer primary and the enclosure is of the same order of magnitude as the impedance between the enclosure and earth through the person, a shock hazard exists.

48. EARTH LEAKAGE CURRENT Measurement

49. Measurement of earth leakage current

50. Enclosure leakage current /touch current • LEAKAGE CURRENT flowing from the ENCLOSURE to earth or to another part of the ENCLOSURE through a conductor other than the protective earth conductor.