EBME Forums Forums Management Medical Equipment Management EST Procedures for General Ultrasound

Hi Geoff
Thanks for your reply. Currently we only use IEC601-1 and IEC61010. I guess the ministry is considering adopting IEC62353 in near future. So we just stick on these 2 standards. Without doubts, IEC62353 is very simple and easy way to go, but we still have to stick to our current standards.

Therefore our practice of measuring enclosure (or touch) leakage current for US probe by using CL2;BF;0AP or CL2;CF;0AP (by immersed the probe with gel and wrap it using aluminium foil and attaching the ground/enclosure probe onto the foil) is acceptable? At the mean time doing another test for console unit by using CL1;B;0AP. By performing the test with 0AP, there will be no "mains on applied part" test conducted and we will be safe from frying the probes or even ourselves. I guess this practice is fine and doable. What do you think?

Besides this, is there any limit on the leakage current for US probe, I ever seen 185uA for TEE probe, how about the other US (eg linear, vagina, convex & etc)?

As I have probably said many times before, in general (and regardless of which Standard is being followed) I believe there are three pertinent measurements to be carried out during routine electrical safety testing (that is, during normal servicing or maintenance). These are:-

1) Grounding resistance (plug earth pin to unit)
2) Line and Neutral to Earth insulation
3) Risk current

By "risk current" I mean enclosure leakage with the protective earth conductor open circuit. This is the maximum current that could flow through the patient if the ground becomes open and chassis becomes live (ie, if a double-fault condition arises). It should be called "risk current" to distinguish it from "touch current" under SFC. I would test for "risk" (rather than "touch") current, as this represents the worse case, and one that could actually occur under fault conditions.

Note that in well-maintained machines (that is, as long as earth continuity is preserved), the "double-fault condition" mentioned above is very unlikely to occur, as the equipment fuse or breaker will blow if the chassis becomes live in the event of a fault (due, for example, to liquid ingress and [or] component failure). Note also that whatever the maximum allowable "risk current" is, it will still be way below the level of perception (typically 1 mA), and well below harmful levels of current.

Note also that the fuse(s) will blow in the event of a drastic breakdown in basic insulation (test 2). So, if you are behind schedule (and who isn't?), and have time for only one EST:- again, "risk" is the one to go for (in my opinion).

I'm sure that folk on here don't need reminding, but (for completeness) it can be seen, therefore, that the integrity of the grounding conductor is the essential element of electrical safety.

Regarding probes on ultrasound units, I doubt you will find any exposed metal parts there that are also earthed, so (in principle) wrapping metallic foil around the probe, and slapping on a dollop of gel sounds like a pretty creative method, as long as such effort is considered worthwhile. See if you can detect any risk current that way, measured from the probe (or the foil) to true earth (eg, the earth connector on the wall outlet - hopefully).

I would need to refer to manufacturers' specs before commenting on leakage current values for specific probes. But are they talking about "risk current" ... and how do they measure it? Foil and gel?

And (lastly) what sort of readings are you getting in practice? And have you failed any of the probes due to poor electrical safety?

Meanwhile, here's a link that you may find interesting.

And here's a .pdf about probe failures.

And (again, lastly) if you really want to do the job properly, it looks like you need something like the Fluke ULT-800. Take a look at the manual. No doubt you shall be encouraged to note that it uses a method similar to the one you are already using! Notice, however, that all you seem to get for such expense is a PASS/FAIL indication, which (as you have already mentioned) looks to be 185 uA.

The ULT-2000 from BC Biomedical looks a bit more, er, technical.

Hi Geoff,
Thanks for your reply. ULT-800 and ULT-2000 is an another alternative for this, but it is not economical to purchase this analyzer we have too many US with sooooooo many manufacturers and model (Japan, US, Taiwan, Korea, China & etc), I believe some of the US probe adapter might not available. That is the reason why we are using our current method, which serve the same purpose by measuring the leakage current of the probe, and it applies to all models.

Thanks a lot for the reference and nice websites. Appreciated.

Hi Geoff,
For automatic EST, it would be in single fault condition. But for Manual, we are doing according to the form given. (I'm so sorry for not able to show the form here as it is a controlled form, company's policies). Based on the form we used for manual EST, we are actually performing DFC.



Totally agreed with you. The integrity of the grounding conductor and connection is the basic element of the Electrical Safety.



So far we only getting value from 0-5uA, nothing more, and we haven't failed in any electrical safety. Usually we will halt EST when we found the probe is damaged, cable exposed, kinked, hole, scratches & etc. We will have to correct the problem by repair it (buy new probe if the repair is not successful), then we will perform EST as the last procedures before completing the work.

I recently came across this nice .pdf about testing ultrasound probes.

On the same note,something from our German colleagues:

https://www.gossenmetrawatt.com/english/produkte/seculife-ul.htm

Looks nice, Malcolm. Have you got one?