Understanding clause 15.4.2.1 d) of amendment 1:2012?

[Roland chung]

Hi all,

Clause 15.4.2.1 d) of amendment 1:2012 states that loss of function of MEE caused by operation of a thermal cut-out or over-current release shall not result in the loss of ESSENTIAL PERFORMANCE.

But in the real world, clinical function will usually loss when the protector operates since the power supply of equipment (or of part of equipment) will be shut down. So it is difficult to fulfil this requirement.

Could you please share your point of view?

Thanks,
Roland

 

[Pads38]

Re: How to understand clause 15.4.2.1 d)?

Hullo Roland,

Slight correction,

Loss of function of the ME EQUIPMENT caused by operation of a THERMAL CUT-OUT or OVER-CURRENT RELEASE shall not result in a HAZARDOUS SITUATION.
Compliance is checked by inspection of the design documentation and the RISK
MANAGEMENT FILE.

But there will be times where clinical performance has to be maintained. I guess then you would need duplicate temperature control systems rather than a cut-out.

 

[Roland chung]

Re: How to understand clause 15.4.2.1 d)?

Hi Pads38,

Thank you. The requirement you quoted is from 60601-1:2005, but I am talking about A1:2012.

Regards,
Roland

 

[Peter Selvey]

Re: How to understand clause 15.4.2.1 d)?

In A1, essential performance is separated under normal condition and single fault condition. Typically we don't expect full performance under fault condition, but for higher risk devices there may be minimum functionality or special limits that apply.

For example a surgical laser may have the following specs:

EP/NC: +/-5% of set power
EP/SFC: not exceed more than 20% of set power

For lower risk devices, there may be no EP in SFC (in which case it should be explicitly stated as such). For example a low risk temperature monitoring function:

EP/NC: +/-0.3C
EP/SFC: No requirement

A thermal cut out should only operate in SFC, so it would pick up the EP/SFC limits, not the EP/NC limits. A high risk device might define EP/SFC as being able to provide an alarm in case of loss of function, i.e. when the TCO opens.

 

[Roland chung]

Re: How to understand clause 15.4.2.1 d)?

Does it mean that alarm is an alternative to the loss of essential performance for high risk equipment (e.g. infant warmer)? From the risk analysis, it is convincing. But from the literal meaning of standard, essential performance should be maintained (no matter NC/EP or SFC/EP).

No clinical functions are possible if the thermal cut-out inside the infant warmer operates under single fault condition.

 

[Peter Selvey]

Re: How to understand clause 15.4.2.1 d)?

A1 clearly indicates that EP is not static and should be considered separately for normal condition and SFC, so at least two distinct specifications. But I expect eventually we will see that essential performance is highly context sensitive, not just these two levels. Different abnormal events like operator error, low battery, loss of mains supply, genuine hardware faults, EMC interference all occur at varying probabilities, so variable specifications make sense.

For example a electronic home use thermometer might have the following EP:

Ambient temp 15-40: +/-0.2C accuracy
Ambient temp 0-50: +/-0.4C accuracy
Low battery: blank display, show low battery symbol
After 20cm immersion test: no effect (specified accuracy)
After being dropped from 1m 3 times: no effect (specified accuracy)
After vibration test: No effect (specified accuracy)
After ageing test: No effect (specified accuracy)
High humidity test: No effect (specified accuracy)
EMC 3V/m: No effect (specified accuracy)
EMC 10V/m: Specified accuracy or blank display
SFC (in measurement circuit): blank display, show error function
SFC (excluding measurement circuit): no requirement

This is just a conceptual example off the top of my head, not a real suggestion for a design specification and obviously not a complete list of conditions (contexts).

 

[Roland chung]

I would like to know which clause indicates the ESSENTIAL PERFORMANCE is dynamic?

 

[Peter Selvey]

In the revised Clause 4.3:

The MANUFACTURER shall then specify performance limits between fully functional and total loss of the identified performance in both NORMAL CONDITION and SINGLE FAULT CONDITION.

Also check out the note, it has an example which fits exactly with the start of this thread