Case study
A patient warming system that passed safety testing first time
How Pinetics designed a 1000 W convective patient warming system, end to end, that passed IEC 60601 testing first time and gained CE and CDSCO approval.
At a glance
Client
A medical device company in Asia
Product
A convective patient warming system for perioperative hypothermia
Pinetics' scope
The full product, end to end: control and power electronics, firmware, fan and airflow control, the touch screen user interface, and the design and test documentation
Outcome
Passed IEC 60601 safety and EMC testing in the first round with no redesign, delivered on time, approved under EU MDR (CE marking) and by CDSCO in India, and now in use in hospitals
What did the client need?
Patients lose body heat during surgery, and low body temperature in the perioperative period slows recovery. The client needed a warming unit that blows filtered, temperature-controlled air into disposable blankets, holds the set temperature steadily up to 43 degrees Celsius, and meets medical electrical safety standards for use next to a patient.
What did Pinetics build?
A modular system with a separate control board, power board and temperature sensor modules:
- Control board on an ST processor, running a PID algorithm for accurate and stable temperature, onboard self-diagnostics, and audio and visual alarms.
- Power board with high current density, delivering 1000 W to the heater.
- Airflow from a BLDC fan with PWM speed control, through a HEPA filter, keeping the blankets inflated with even heat across them. Blower speed and temperature are selectable, from ambient up to 43 degrees Celsius.
- User interface on an LCD touch screen, built in TouchGFX.
- 4-layer boards with high component density.
What was the hardest part of the project?
Two problems at once. The unit has to drive 1000 W of heating while still meeting the isolation, leakage current and electromagnetic emission limits of IEC 60601. And it has to keep a steady flow of warm air through a HEPA filter and a disposable blanket whose resistance to airflow changes from one setup to the next.
How did the team solve it?
- Safety designed in from the first schematic. Isolation, creepage and leakage current were designed in from the start, then checked with pre-compliance tests before the formal laboratory.
- EMC designed in early. Filtering, layout and switching were chosen for CISPR 11 from the start, with pre-compliance scans before the formal test.
- Closed-loop airflow. Fan speed and heater power are controlled together by PID against the measured air temperature, so the flow and temperature stay steady as the filter and blanket load change.
- An independent cut-off. An over-temperature cut-off works separately from the main controller, so a firmware fault cannot overheat the patient.
Which standards did the design meet?
- IEC 60601-1 (basic safety and essential performance)
- IEC 60601-1-2 (electromagnetic compatibility)
- IEC 60601-2-35 (particular requirements for heating devices using blankets, pads or mattresses)
- CISPR 11 (electromagnetic emissions)
- IEC 62304 (medical device software life cycle)
- IEC 62366 (usability engineering)
- Design outputs delivered inside the client’s ISO 13485 quality system
What was the result?
The system passed IEC 60601 safety and EMC testing in the first round, with no redesign, and was delivered on time. It is approved under the EU MDR (CE marking) and by CDSCO in India, and is in use in hospitals.
“Our patient warming device had strict IEC 60601 requirements and tight timelines. Pinetics handled the entire hardware and firmware stack, including PID control and safety compliance. Delivered on time, passed all testing first round.”
CEO, medical device company in Asia
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