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Electromagnetic Interference

Electromagnetic Interference. Hospital Device Immunity. RF Transmitters. RF Transmitters – 2 Major Categories: Intentional Portable (handheld or mobile): Cellular Telephones, 2-Way Radio, Telemetry Installations: Paging Tower, Broadcast, Radar Unintentional

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Electromagnetic Interference

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  1. Electromagnetic Interference Hospital Device Immunity

  2. RF Transmitters RF Transmitters – 2 Major Categories: • Intentional • Portable (handheld or mobile): Cellular Telephones, 2-Way Radio, Telemetry • Installations: Paging Tower, Broadcast, Radar • Unintentional • Electrically powered equipment including Medical Devices • Nature

  3. RF Transmitters Effective Radiated Power • Function of Output Power and Antenna Efficiency • Usually fixed except Cellular • More power = greater range at same wavelength

  4. RF Transmitters Field Strength (V/m) Distance dependant • In free space far field strength is inversely proportional to distance • Reflections can cause higher than expected strength • Referenced to wavelength

  5. RF Transmitters Wavelength • Short wavelength (high frequency) more problematic than long wavelength (low frequency) • Conductors measuring ¼ or ¾ of the wavelength are most susceptible to interference

  6. RF Propagation • Radiation Transmitter and Receiver E.g. Radio or TV Broadcast Transmission • Conduction Physical connection Does not need to be directly coupled E.g. ESU coupled to Pt. monitor via Pt. • Induction Magnetic or Capacitive coupling E.g. signal cables routed parallel to each other

  7. EMI Induced Problems • Bit Corruption Associated with digital devices Artifact changes byte value Usually fixed with error detection schemes • Junction Rectification Associated with analog devices High frequency AC produces DC at semiconductor junction Produces DC off set voltage or modulated signal

  8. Electric Field Strengthin Hospital locations(500 kHz to 1.5 MHz)

  9. Ad Hoc Testing • Simultaneous learning, test design and test execution. • Informal, one time testing with no designed procedures. • Flexible, customized procedures for task at hand. • Generally exploratory in nature – sometimes called Exploratory Testing.

  10. Ad Hoc Testing • Must incorporate reporting procedure • Need a method to quantify and compare data collected • Test data should be reproducible! • Useful for defining formal test procedures.

  11. Electromagnetic Vulnerability Medical Device Selection Criteria

  12. Electromagnetic Vulnerability • Criticality of the Device Is it life supporting Critical patient monitoring Diagnostic Medication delivery • Impact of Device Failure Potential of injury or death to patient Can it cause harm to staff

  13. Electromagnetic Vulnerability • Compliance with applicable EMC Standards Has the device been tested for EMC by an outside party? • Known EMI Problems with Device Type of device, model or manufacturer history. • Suspected EMI Problems with Device Erratic performance of device

  14. Electromagnetic Vulnerability • Sensitive Components or Circuitry High gain amplifiers, microprocessors, patient leads, any antenna resembling traces • Frequent No Fault Found Repairs Repeated reported issues with device yet testing reveals no anomalies OR problems disappear when removed from user area

  15. Device Immunity to RF • Hospital devices have conductors of various lengths. • Many of these devices are designed to amplify very weak signals. • Many of these devices have connecting wires that can act as antennas.

  16. EMI Recognition • Device works in shop but is erratic on floors. • Patient’s condition does not match data provided by device. • Intermittent malfunction during certain weather conditions or when transmitter is nearby. • Inexplicable alarms

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