3.1 Importance of testing

Testing a microcontroller-based system means checking, by planned measurements and trials, that the hardware and firmware do what the design requires, safely and reliably, before the system is put into use and after every repair or change. In biomedical equipment such as infusion pumps, patient monitors, incubators and syringe drivers, a hidden fault can injure or kill a patient, so testing is not optional: it is required by standards such as IEC 60601-1 (safety of medical electrical equipment), IEC 62304 (medical device software life cycle) and IEC 62353 (tests after repair and in service). Example: the biomedical engineering unit at Mama Lucy Kibaki Hospital in Nairobi tests every repaired infusion pump controller with a flow analyser before it returns to the wards.

Reasons for testing

• Patient and user safety: Confirms that the system cannot give a dangerous output (for example over-infusion, overheating or electric shock) and that alarms and safety cut-outs work.
• Correct function: Confirms that every input, output and function behaves as the specification requires.
• Accuracy of measurements: Confirms that readings (temperature, pressure, heart rate) are within the stated tolerance, since clinical decisions depend on them.
• Early detection of faults: Finding a fault on the bench is cheaper and safer than finding it in a ward.
• Compliance with standards and regulations: Test records are evidence for regulators (the Pharmacy and Poisons Board for medical devices in Kenya), accreditation bodies and insurers.
• Reliability: Burn-in and stress tests reveal weak components and timing faults before the device is in service.
• Verification of repairs and modifications: After a component or firmware change, tests prove that the fault is fixed and nothing else was disturbed (regression testing).
• Documentation and traceability: Test results become part of the device history and support future fault-finding.
• User confidence: Clinicians trust and use equipment that is known to be tested.

When testing is done

Consequences of inadequate testing

• Patient harm: Wrong drug dose, missed alarm, burns or electric shock.
• Equipment damage: A short circuit or software lock-up can destroy outputs and sensors.
• Costly recalls and downtime: Faulty units must be withdrawn, repaired and retested.
• Legal and professional liability: Failure to test and record can lead to disciplinary or legal action.
• Loss of reputation: For the hospital, the supplier and the technician.

Testing and the system blocks

A microcontroller measurement or control system is tested block by block and then as a whole:

• Sensor and signal conditioning: Amplifiers, filters and level shifters (see 3.2.6).
• Signal processing: The analogue to digital converter and the firmware that calculates results (see 3.2.7).
• Data presentation: Displays, alarms, printers and data links (see 3.2.8).
• Power supply and protection: Correct voltages, ripple, battery backup and protection circuits.
• Integrated system: All blocks working together under realistic conditions (see 3.5.11).