My question is in regards to biopotential amplifiers, more specifically an instrumentation amplifier as part of an ECG.

I know that IEC60601 states that a paitent must be limited to 50uA under fault conditions.

What type of methods are used to ensure a paitent does not get a shock and receive current of 50uA and above?

  • \$\begingroup\$ A place to start is a search on “intrinsic safety”. This concerns the prevention of arcs that could cause explosions in explosive atmospheres. This is not the same as your problem, but the thinking is going to be much the same, that is, the limiting of current even under fault conditions. \$\endgroup\$ – Robert Endl Jan 17 '18 at 20:27
  • \$\begingroup\$ Ah, thank you, that's really useful, I'll give it a google later. \$\endgroup\$ – user131618 Jan 17 '18 at 21:03

Suppose you have designed a device. Now you have to review how it can fail. You perform a formal Failure Modes and Effects Analysis (FMEA) to determine what happens when each component fails.

You know how the patient is connected to the equipment. The patient is likely to be connected to earth.

If you know what happens when each component fails, you can determine what will happen to the patient. For instance, suppose a resistor failing short circuit could lead to excessive current flow through the patient to earth. This is an unacceptable failure effect of the circuit and must be mitigated before the design complies with the standard. The exact methods used to mitigate hazards depend entirely on the circuit design, system design, and intended use.

Beyond the FMEA, other statistical safety analyses may be required depending on the complexity of the system and its relevant regulatory requirements. In the aircraft systems I work on, the FMEA feeds into a fault tree analysis (and many other documents) that tells you how likely each fault is. The probability of a fault and its associated hazard play into each other. More critical faults are required to have a lower probability of occurrence.

The ultimate goal is to show that, under all foreseeable operating and fault conditions, that there is a very high level of confidence patient will not be exposed to hazardous levels of electrical energy.


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