Hi, I have a question acc. auxiliary current. It concerns an invasive blood pump, the connection cable for the pump is inserted through the abdominal wall. 8.7.4.8 requires the use of a suitable measurement supply circuit, unless the MEDICAL DEVICE has only a single PATIENT CONNECTION. Does this mean that this clause is not applicable in this case?
Auxiliary current blood pump
- Thread starter Charango
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Dimitri CHEN
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8.7.4.8 is measurement of the patient anxiliary current, to have a patient auxiliary current, there should be at least two patient connection(to form a circuit).
so 8.7.4.8 is to state that if the EUT has only one patient connection(which means you cannot have a patient auxiliary current), the figure 19 is NA. so the question is to analysis whether your device have multiple patient connections or only one.
so 8.7.4.8 is to state that if the EUT has only one patient connection(which means you cannot have a patient auxiliary current), the figure 19 is NA. so the question is to analysis whether your device have multiple patient connections or only one.
It's there but not a usually a concern in practice. In theory, there must be insulation between the wires (e.g. each motor drive lead) and the patient that needs to prevent the auxiliary currents. However this insulation also needs to also pass 1500Vrms for CF insulation which is a much higher requirement, so generally this is the one that takes the focus in design and testing. A caveat is that if the wires separate to different locations in the body, have long lengths and the motor drives have higher frequency components (e.g. kHz) and each motor could have different drive waveforms (e.g. PWM with separate feedback), there is a real possibility of capacitively coupled currents flowing through the insulation and into the body. However I would be surprised if these were anywhere near the limits and are almost certainly not dangerous due to the low current density (highly spread out).
Thank you for your comprehensive assessment. CF isolation is in place. I will check again for any possible influence of capacitively coupled currents, as the individual phases of the pump have different drive waveforms. But I also think that these do not reach the limit values.
