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High leakage on diathermy
#75806 13/11/20 1:47 PM
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Howard Offline OP
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I have just performed some testing on some quite old diathermy, TD830, still in use.
The output tests were exactly as we expected, then we moved onto the leakage tests. The tests had previously been performed using an older ESU analyser, on that analyser the diathermy passed its tests.

On the new one, the leakage was recorded as up to 230mA, that 150% of the IEC limit of 150mA. The very high leakage was seen for just one second, right at the start after activation, then it settled down to 120 ish mA, but it was still over the limit. It was repeatable, and happened on all outputs.

Has anyone else ever seen this type of leakage? Am I correct to read that the limit should not be exceeded, even for a split second?

Re: High leakage on diathermy
Howard #75808 13/11/20 4:09 PM
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Hi Howard, hopefully your Bipolar values are within limits?? Impedance value between Active and Neutral is over 2M ohms??

I've had a quick re-read of the Norm, it doesn't actually specify the the value measured is to be considered an instantaneous value or not, I cant see how that would the case as the measured value would be too reliant on the tester being used....

Hopefully Geoff will jump in.......

I personally record the steady value during our testing

Stay Safe

Malcolm.

Re: High leakage on diathermy
Malcolm #75810 13/11/20 6:38 PM
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Thank you Malcolm; yes, electrosurgical units were always one of my "specialist subjects"!

The equipment under consideration (TD-830) has "leakage limiting" circuitry ... but the question must be:- how long does it take to kick in (respond)? Not fast enough to out-wit Howard's nice tester, I'm guessing.

That's part of the problem with a lot of modern biomed test equipment ... it's smarter than (out-performs) the kit it's meant to be testing (and often the testing Standard(s) as well).

In Happy Days of Yore we had to make do with whatever we had to hand - sometimes just a piece of fresh liver from the cookhouse!

Meanwhile, and as we're talking about ESU testing ... what about the "accessories"? Often (usually?) overlooked, but still potentially dangerous.

PS: yes; "steady value during ... testing" - always let things settle to steady state (unless, of course you're deliberately trying to capture a "spurious signal").


If you don't inspect ... don't expect.
Re: High leakage on diathermy
Howard #75811 13/11/20 6:44 PM
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@Howard ... there's always the possibility that the TD-830 is faulty, of course. Deteriorating component(s) or what-have-you.

It would be nice if you were able to compare it against other TD-830's. Don't forget that we're talking about RF (MF in this case), where strange things can (and do) happen.

Even nicer would be to test a selection of TD-830's (plus other types, if available) with both your own test equipment and a few of those now available from other suppliers; and then compare results.

I have found that the various ESU Analyzers can cough up quite dissimilar results; and also that various ESU manufacturers expect different testing methods (test equipment, loads, circuits etc.) to be employed. All that may not matter much in hospitals with only one type of ESU and test kit, but it can all get a bit fraught* for the "wandering biomed" (who is usually has no choice but to use whatever test kit he finds at site).

Which Outputs are (were) in play when you saw the instantaneous high leakage? What did (does) the 'scope show? (there are some nice output waveforms shown in the TD-830 manual)

My main concern would always be that Outputs fall within limits at the various settings (and for all ESU's of the same type to give the "same" Outputs - again with limits). But, happily, I notice that you report that Outputs are OK

Personally, I wouldn't worry too much about a bit of excess leakage current; it passes harmlessly "down the drain" after all. I would simply keep my eye on it, as it were; perhaps shorten the PM interval and see if it gets any worse. Risk has to be balanced; to my mind, by far the biggest risk to the patient is (will be) the surgeon merrily blazing away!

* fraught ... not a word that we see very often on here.


If you don't inspect ... don't expect.

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