TonKuijper
Registered
Hello experts,
(sorry for my long first entry)
My question is about ME EQUIPMENT, Class IIa, type CF.
That means a SINGLE FAULT CONDITION PATIENT LEAKAGE CURRENT of max.50uA.
I went through loads of information on the internet and always see examples that have to do with mains voltages of 230V on the PATIENT APPLIED PART against real ground.
The instrument under test is in a plastic housing with no touchable metal parts.
The system consists of a network interface on a PC cart connected by a cable tot an amplifier near the patient.
The network interface is powered by a 24V DC adapter and the amplifier has an internal DC/DC converter from 24V to 5V. Both the adapter and the DC/DC converter are isolated and Certified for IEC 60601-1, 3rd edition type CF.
The 5V is linear regulated inside the amplifier to +2.05V and -1.25V (total 3.3V).
My problem with the Test House:
The SINGLE FAULT CONDITION (SFC) PATIENT LEAKAGE CURRENT exceeds the maximum value of 50 uA when they short the Clearance/Creepage at the secondary (floating) side.
This is according to clause 8.7.1 in the test report.
The electrode inputs are protected with series resistors (size 0603) to limit single fault currents to approx. 10uA (max. allowed is 50uA) in case the electrode shorts to the power supply of max. 2.05V due to a worst case (full short to VCC) active component failure.
These resistors are on the amplifier PCB and all floating circuits have an adequate creepage/clearance distance to the 24V input of the DC/DC converter.
Data communication is with an IEC 60601-1 type CF certified digital isolator.
The limiting resistors have a normal (small) distance to the other (floating) circuitry on the PCB.
Is this distance the creepage/clearance that must be shorted in the SFC test?
I understand from the IEC 60601-1 that a SFC condition can also be TWO SFC’s if the first is not detectable. The limiting resistor is bypassed by a capacitor to lower the impedance and can fail shorting without being noticed. One must assume that later an active component can fail while the limiting resistor is a short.
Is this shorting in the test something normal for this clause 8.1.7 SFC test?
Or is it only needed for the DC/DC converter isolation (already done by the manufacturer for the certification).
(sorry for my long first entry)
My question is about ME EQUIPMENT, Class IIa, type CF.
That means a SINGLE FAULT CONDITION PATIENT LEAKAGE CURRENT of max.50uA.
I went through loads of information on the internet and always see examples that have to do with mains voltages of 230V on the PATIENT APPLIED PART against real ground.
The instrument under test is in a plastic housing with no touchable metal parts.
The system consists of a network interface on a PC cart connected by a cable tot an amplifier near the patient.
The network interface is powered by a 24V DC adapter and the amplifier has an internal DC/DC converter from 24V to 5V. Both the adapter and the DC/DC converter are isolated and Certified for IEC 60601-1, 3rd edition type CF.
The 5V is linear regulated inside the amplifier to +2.05V and -1.25V (total 3.3V).
My problem with the Test House:
The SINGLE FAULT CONDITION (SFC) PATIENT LEAKAGE CURRENT exceeds the maximum value of 50 uA when they short the Clearance/Creepage at the secondary (floating) side.
This is according to clause 8.7.1 in the test report.
The electrode inputs are protected with series resistors (size 0603) to limit single fault currents to approx. 10uA (max. allowed is 50uA) in case the electrode shorts to the power supply of max. 2.05V due to a worst case (full short to VCC) active component failure.
These resistors are on the amplifier PCB and all floating circuits have an adequate creepage/clearance distance to the 24V input of the DC/DC converter.
Data communication is with an IEC 60601-1 type CF certified digital isolator.
The limiting resistors have a normal (small) distance to the other (floating) circuitry on the PCB.
Is this distance the creepage/clearance that must be shorted in the SFC test?
I understand from the IEC 60601-1 that a SFC condition can also be TWO SFC’s if the first is not detectable. The limiting resistor is bypassed by a capacitor to lower the impedance and can fail shorting without being noticed. One must assume that later an active component can fail while the limiting resistor is a short.
Is this shorting in the test something normal for this clause 8.1.7 SFC test?
Or is it only needed for the DC/DC converter isolation (already done by the manufacturer for the certification).