Handheld instruments
Figure 1. Power stage design in medical equipment to meet MOP.
compliance with MOPP standards, robust isolation is essential to safeguard patients from electrical hazards. These devices include electrocardiogram (ECG) monitors, which measure heart activity; infusion pumps, which deliver precise doses of medication; ultrasound probes, used for diagnostic imaging; and defibrillators, which administer high voltage shocks to restore heart rhythm.
The operator-only devices, which are used by medical staff without direct patient contact, typically require compliance with MOOP standards. While the isolation requirements are less stringent, these devices still demand high reliability and performance. Examples include laboratory analysers for blood and tissue analysis, diagnostic imaging systems like magnetic resonance imaging (MRI) and computed tomography (CT) scanners, and medical workstations used for visualisation and control.
DESIGN STRATEGIES FOR MOP COMPLIANCE Risk-Based Design
Risk analysis is a fundamental approach in the development of medical electrical equipment, ensuring both safety and regulatory compliance. The process begins with a comprehensive risk assessment, guided by standards such as ISO 14971 risk management process and IEC 60601-1. This assessment involves evaluating the device’s intended use, the environment in which it will operate, and the characteristics of its users - whether they are healthcare professionals, caregivers, or patients.
Critical considerations include whether the device will be used in a clinical, home, or mobile setting and whether it will be operated by trained personnel or lay users. A key aspect of the assessment is determining the nature of the device’s interaction with the patient. If the device
Instrumentation Monthly May 2026
does not make direct contact with the patient, such as in the case of laboratory analysers or imaging equipment operated remotely, compliance with MOOP may be sufficient. However, if the device interfaces with the patient - either invasively, like catheters and probes, or non-invasively, like ECG electrodes - then MOPP compliance becomes mandatory. Additionally, the design must account for single fault conditions, ensuring that the device remains safe even if one protective measure fails. This is a core requirement of IEC 60601-1, which mandates testing under both normal and fault conditions. All risk management activities, including hazard identification, risk estimation, control measures, and verification of safety features, must be thoroughly documented. This documentation supports regulatory submissions and audits, providing traceability and justification for design decisions based on risk analysis.
Isolation Techniques
Isolation is a fundamental design strategy in medical electronics to ensure patient and operator safety, particularly in compliance with MOOP and MOPP. These requirements mandate isolation between high voltage and low voltage domains to prevent hazardous voltages from reaching sensitive circuitry or the patient interface. Figure 1 illustrates achieving the means of protection requirements for an AC/DC power supply in a medical device application with enough insulation to protect the operator and patient.
To achieve this, designers employ a variety of isolation components and techniques, each with distinct advantages and trade-offs:
1. Isolation Transformers
These are commonly used in power supplies to provide galvanic isolation between input and output. Medical-grade isolation transformers are
specifically engineered to meet high dielectric strength (often several kilovolts) and ultralow leakage current specifications, which are critical for patient safety. They are robust and reliable, making them ideal for applications requiring continuous power delivery with high integrity.
2. Optocouplers (Optoisolators) Optocouplers use a light-emitting diode (LED) and a photo-detector to transmit signals across an isolation barrier. The electrical signal is converted to light, transmitted across a non-conductive gap, and then converted back to an electrical signal. While optocouplers are effective and widely used, they have limitations such as slower signal transmission speeds, limited bandwidth, and potential degradation over time due to LED aging. These factors can affect long-term reliability in high performance systems.
3. Digital Isolators
Digital isolators such as iCoupler are modern alternatives to optocouplers, utilising capacitive, magnetic, or RF coupling to transmit digital signals across isolation barriers. They offer significant improvements in speed, data integrity, and longevity. Unlike optocouplers, digital isolators are not subject to LED wear-out mechanisms, making them more suitable for high-speed communication interfaces such as SPI, I²C, or UART in medical devices. Additionally, many digital isolators are designed to meet reinforced isolation standards, supporting both MOOP and MOPP requirements.
4. Isolation in Communication Interfaces For systems with external connectivity (for example, USB, Ethernet), isolation is also required to prevent ground loops and fault propagation. Isolated transceivers and isolation ICs are used to maintain signal integrity while protecting the
Continued on page 48... 47
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72
