EET116 Electrical Engineering Technology for Biomedical and Biometric Students Study Notes

Introduction to Workshop and Electrical Safety

• Fundamental Principle: Safety is the fundamental pillar of medical engineering. Workshops are designated as high-risk areas where improper tool usage or a lack of attention can result in severe physical injuries.

• General Workshop Hazards:

  • Physical Risks: These include moving machinery parts, rotating shafts, and workpieces with sharp edges. These can cause entanglement, cuts, or crushing injuries.

  • Environmental Dangers: Risks such as cluttered workbenches, trailing wires, and slippery floors contribute to high incidences of slips, trips, and falls.

  • Hazardous Materials: Direct exposure to toxic fumes, dust, or chemicals can lead to serious respiratory issues or caustic skin burns.

• Electrical Hazards:

  • Electric Shock and Burns: Caused by direct contact with live wires or faulty equipment.

  • Arc Flashes: This occurs when electricity jumps through the air between conductors, producing extreme heat and potential explosions.

  • Equipment Failure: Common triggers for fires include frayed cords, overloaded circuits, and damaged plugs.

• Protocol for Handling Electrical Accidents:

  1. Switch OFF the power supply immediately.

  2. Do NOT touch the victim with bare hands while they are in contact with the source.

  3. Use an insulated material to move or separate the victim from the live component.

  4. Call emergency services immediately.

  5. Provide necessary first aid.

Importance of Safety Procedures and Personal Protective Equipment (PPE)

• Purpose of Safety Procedures: These are standard directions designed to eliminate or minimize identified risks.

• Accident Prevention - Lockout/Tagout (LOTO): Adhering to LOTO procedures ensures that machinery is completely de-energized during maintenance activities to prevent accidental startup.

• Iris Recognition Technology: Iris recognition is noted as the only biometric technology that remains functional while personnel are wearing full PPE, including masks, gloves, goggles, and hoods.

• Types of Personal Protective Equipment (PPE):

  • Eye Protection: Safety glasses or goggles designed to protect against debris and chemical splashes.

  • Hand Protection: Insulated rubber gloves specifically rated for electrical work.

  • Foot Protection: Steel-toed boots providing a shield against falling objects.

  • Head and Hearing Protection: Hard hats for impact protection and earplugs for environments with loud machinery.

Call and Alarm Circuits in Healthcare

Biometric and biomedical students must understand the systems facilitating patient safety and facility security.

• Patient/Nurse Call System:

  • Purpose: This is a critical communication circuit typically utilizing a low-voltage ($24\,V$ DC) bus. It functions to latch an alarm from a patient's room until it is manually reset by staff, enabling quick response and improved safety.

  • Wiring and Infrastructure:

    • Utilizes a star or bus wiring system.

    • Uses low-voltage ($24\,V$) communication cables (2-core or 4-core).

    • Requires backup power (battery or UPS).

    • The use of fire-resistant cables is highly recommended.

  • Key Components:

    • Input: A normally open (NO) push-button or a bathroom pull-cord.

    • Controller: A microprocessor (e.g., ATmega series) or a latching relay. A single controller can handle up to 10 rooms or zones.

    • Outputs: Includes a dome light (located outside the room), a buzzer, and a central annunciator panel at the nurse station.

    • Reset: A physical cancel button must be located specifically at the patient's bedside to ensure the physical presence of staff.

  • Wiring Diagram Specifics (Wiring Colors and Assignments):

    • Patient Call Station: Red (CALL), Yellow (CANCEL), White (AUDIO), Black (GND).

    • Call Controller Connections: Green (CALL IN), Gray (CANCEL IN), White (AUDIO IN), Orange (SPEAKER), Blue (CALL - Duty Station), Brown (BED EXIT), Purple (LIGHT OUT).

    • Duty Station: Notifies and alerts nurses in common areas or hallways.

    • Bed Exit Monitor: Connected to BED EXIT (Brown) and GND (Green).

    • Over Door Light: Connected to LIGHT (Purple) and GND (Black).

• Fire Alarm Systems:

  • Healthcare Specification: Systems are "intelligent" or "addressable," pinpointing the exact fire location. They are designed to be single-fault proof.

  • Components:

    • Detection Loop: Includes optical or ionization smoke detectors, heat detectors, and Manual Call Points (MCP).

    • Control Panel (FACP): The system "brain" managing the loop and a $24\,V$ battery backup.

    • Notification Appliances: Horns, strobes, and bells.

    • Circuit Integrity: An End of Line (EOL) resistor is placed at the end of the loop to monitor for wire breaks. Typical resistor values seen in diagrams include $4.7\,k\Omega$ and $10\,k\Omega$.

  • System Types:

    • Conventional: Divides buildings into zones; shows the zone but not the specific room.

    • Addressable: Each device has a unique address for exact location identification. Handles up to 99 devices per loop (approx. $3.3\,km$).

    • Wireless: Uses radio signals; ideal for heritage buildings.

    • Aspirating: Extremely sensitive; uses fans to draw air through pipes to detect smoke particles early.

• Burglar (Intrusion) Alarms:

  • Wired Systems: High reliability, low maintenance, physical cables.

  • Wireless Systems: DIY-friendly, portable, uses radio frequencies (Wi-Fi/Cellular).

  • Hybrid Systems: Combines wired core areas with wireless peripheral sensors.

  • Wiring/Zone Types:

    • Normally Closed (NC): Most common; opening the circuit triggers the alarm.

    • Normally Open (NO): Circuit is incomplete until a sensor (like a pressure mat) activates.

    • EOL Resistor Wiring: Allows the panel to detect three states: Normal (secure), Alarm (tripped), and Tamper (wire cut/shorted).

Installation Cables and Wiring Systems

• Standard Security Wire:

  • $22/2$ (2-conductor stranded) for simple contacts.

  • $22/4$ (4-conductor stranded) for powered devices like motion sensors (two for power, two for signal).

• Factors for Choosing Wiring Systems: Durability, cost, safety, and environment (heat/dampness).

• Special Installations:

  • Flame-proof: Required for explosive gas areas (e.g., oxygen storage).

  • Damp/Electrostatic areas: Moisture-resistant and anti-static wiring for labs and operating theaters.

• Regulations: All installations must follow IEE Regulations.

• Wiring Accessories: Includes switches, socket outlets, junction boxes, lamp holders, and connectors.

• Clinical Wiring Systems:

  • Surface Trunking: Used in labs for ease of modification.

  • Conduit (PVC/Steel): Protects against mechanical damage and Electromagnetic Interference (EMI).

  • Color-Coding: Red is frequently used for UPS and Life Support circuits.

• Installation Design Rules:

  • LSZH Cables: Low Smoke Zero Halogen cables are used to prevent toxic fumes during fire.

  • Separation: Separate circuits for lighting and power.

  • Dedicated Sub-Circuits: High-impact loads (MRI, X-ray) require dedicated circuits to prevent interference.

  • Redundancy: Design ensures a single tripped breaker does not shut down an entire ICU wing.

Power and Lighting Standards in Biomedical Environments

• Cable Rating: Sizing is based on power draw plus "Derating Factors" (heat in ceilings or grouping).

• Voltage Drop: Must be less than $3\%$ for medical electronics to function accurately.

• Socket Color Standardization:

  • White (Normal): Non-essential power connected to the main grid with no backup. Used for computers, printers, and vacuum cleaners. Never use for life support.

  • Red (Emergency/Essential): Powered by backup generators; active within seconds of grid failure.

  • Blue (Uninterruptible - UPS): Seamless power with no flicker; critical for data-sensitive computers and surgical imaging.

  • Orange (Isolated Ground): Reduces electrical noise for high-sensitivity diagnostic instruments.

  • Green Dot: Indicates "Hospital Grade" sockets with enhanced durability and superior grounding.

• Lighting Systems:

  • Dual-Layer Strategy: Ambient ceiling fixtures ($500\text{--}750\,lux$) and Task Lighting ($1,000+\,lux$).

  • Color Rendering Index (CRI): Mandatory CRI of $90+$ for accurate visual assessment of blood and tissues.

  • Hygiene: Fixtures must be IP-rated, sealed, and recessed to prevent dust and allow sterilization.

  • Emergency Requirement: At least $50\%$ of all light fixtures must be on the Red (Emergency) circuit.

  • Circadian Design: Use of Tunable White LEDs to match natural daylight cycles.

Earthing and Protection Systems

• Purpose: Provides a safe path for fault current, prevents equipment from becoming "live," and protects people from shock.

• Critical Need: Patients under anesthesia or connected to electrodes are highly vulnerable to micro-shocks.

• Equipotential Bonding: Linking all metal surfaces (beds, pipes, frames) to a single ground point.

• Components of Earthing:

  • Earth Electrode: Copper rods or plates buried in the ground.

  • Circuit Protective Conductor (CPC): The green/yellow wire in medical device cables.

• Methods: Pipe/Rod earthing (standard buildings) and Mat earthing (high-voltage substations).

• Protective Devices:

  • MCB (Miniature Circuit Breaker): Protects against overcurrent and short circuits.

  • RCD/GFCI (Residual Current Device): Trips if current leaks to prevent electrocution.

  • Isolated Power Supply (IPS): Used in operating theatres so a single fault does not cause a blackout mid-surgery.

• Testing and Lightning Protection:

  • Earth Resistance Test: Must be less than $1\,\Omega$ using a Megger.

  • Fall-of-Potential Method: Standard 3-stake test for hospital grounds.

  • Lightning Protection: Uses arresters and Faraday Cages to protect MRI/CT scanners from atmospheric discharges.

Course Assessment and Resources

• Assessment Strategies: Continuous Assessment Tests (CATs), practical assessments, and a final written examination.

• Core Reading List:

  • Electric Drives (Boldea & Nasar, 2016).

  • Design of Rotating Electrical Machines (Jokinen et al., 2013).