EBME Forums Forums Management Training Surgical Diathermy

I'm concerned about the Ellman Surgitron dual frequency surgical diathermy unit.
This equipment utilises an insulated RF aerial as the return electrode connected to the unit through the standard leg plate electrode connector.
Unfortunately, this allows the user to substitute the standard leg plate electrode for whatever reason.
During IEC601 tests the earth leakage current from the leg plate recepticle pins (socket) was >10 micramps (on two different units - one brand spanking new & the other demo stock) so failing the test. I cannot test leakage at the aerial as it's fully insulated.
The supplier gives the normal answer - no other EBME dept has raised this problem, they are however bringing the 'american designer' to see me.
I have contacted the MDA but still await their advice.
Has anyone else experienced this equipment and if so how did you solve the problem.
Pete

Pete

I haven't seen one of these units so I am guessing blind here.

I assume that the unit works on the principal of the patient return path existing via radiated energy being picked up by the aerial described - fascinating.

If that were to be the case then for the unit to be operable the aerial must be in place. As it is totally insulated it would not come under the description of an accessible conductive part nor is it connected to the patient. You would therefore not expect to be able to measure any current in just the same way as you cannot measure any current in a pulse oximeter probe say, because that too is totally isolated. Remember you are only looking for a single fault condition whereby the mains protective earth is missing, not an additional fault condition where the insulation on the aerial has broken away giving access to a conductive path.

The above hinges round the assumption that the pins of the connector are on the aerial side whilst the female sockets are on the equipment and pass the standard finger test and of not been accessible without the use of a tool

What I would turn to though is inspecting the connectors at the aerial to see if a normal patient plate can be attached by mistake which could lead to problems.

Also I would be intrigued to know the values for RF leakage for this device and its effect on video systems!

Hope this helps but as I said without seeing it I might be barking up the wrong tree!


Brian

Hi Brian,
Thanks for responding but yes you are barking up the wrong tree.
The problem is that the user CAN replace the non patient connected 'aerial plate' with the standard patient connected plate and operate the unit normally.
Unfortunately, this method fails the safety test.
We all know that if it can be used incorrectly, it will be.
regards
Pete

Pete

Ooh err! I think you're quite right to raise concerns over this one.

There's only one thing for sure - Sod's law rules - OK

Brian

BLIMEY !! Th RF generated by this thing must be extorsionate !

I'm really interested to see a copy of the technicall specs for this bit of kit.

Would you know if the user or technical manual is available in PDF format?

Can I have a butchers?

It never ceases to amaze me what these manufacturers are bringing onto the market these days. I know this doesn't solve your problem, however I'd be inclined to agree with the previous posting.

If it has Failed its Elect.Safety test. ITS FAILED.

REJECT IT and move on pal !

Chris-H

Hi folks,
Thanks for the comments, I am being visited by Ellman's MD and the parent company's 'designer' tomorrow, I'll request a PDF version of the manual if available and keep you posted.
I have had a response from the 'MDA'....they are waiting until i've had the above visitation.
Pete

Hi folks,
As promised, here is Ellman's response, drafted by Dr. Frank Lin PhD Director of Engineering.

...This statement is specifically to address the neutral Electrode Monitoring Circuit (NMC) of the Ellman Surgitron 120 IEC Electrosurgical Generator.
The NMC implements an isolation transformer to provide the necessary isolation from patient circuits to meet IEC60601-2-2 safety requirements.
It has a frequency of ~1.3LHz with 5Vpp output voltage between the split neutral plates.
It is an AC low frequency voltage to meet the 12V limitation by IEC60601-2-2 standard 59.10 / monitoring curcuits. The current limitation of the monitoring circuit of the split neutral electrode is specified in 19.3.
As a low frequency leakage current, Table IV of IEC60601-1 applies and the limitation is 100uA....

He goes on to explain the rigorous testing to current standards at two independent test houses, BSI and UL.
From his explanation it would seem that my safety tester, Biotek 601pro, is the culprit.
During leakage tests it performs as follows...
Normal polarity - no fault condition,
it uses the DC limit - and fails.
Reverse polarity - no fault condition,
it uses the AC limit - and passes.
Normal polarity - single fault condition,
it uses the AC limit - and passes.
I will of course be talking to Ultramedic about this problem.
A copy of this explanation letter was sent to the MHRA by Ellman.
Thanks for all the contributions.
Pete

Pete

Just saw your last note re your most "curious' posting. These days of enhanced safety awareness, patient-connected outputs are isolated of course. However, in the early (Diathermy) days of Electro-Surgical units (and ECG machines), the patient plate was always hard-wired to ground potential and quite likely without a sentry circuit. When the sentry circuit came (incase the lead became detached or broken) it used a DC voltage. Then the plate was capacitively coupled to ground with an option for grounding if necessary. And now, as your last entry mentions, in the sentry circuit both AC and DC circuits are completely isolated from ground by a transformer using a low-end kilo-hertz frequency ac voltage. If it had been an old machine, I would have said watch for the DC sentry current as a potential source of problems, as we have always measured DC current as well as AC in safety testing. However, having tried hard to come up with an explanation, I have to agree with you that since two machines were tested and found to give the same results, your tester does seem to be the serious contender for being the culprit.

As for an explanation, sorry I have only one (or possibly one and a half) to offer. If you do not find (and the company have not been able to supply) a satisfactory answer after perhaps delving into the "innards' of your safety tester, and the same fault has not been seen on other safety testing devices you might have tried it on so far, there is the ever-present but very unusual possibility (probably only ever found in radio applications) that the frequency in the patient sentry circuit is being partially rectified (unintentionally of course) by stray coupling from the components, wires etc. either in the unit itself or in your particular safety tester, so causing this erroneous? very small current reading. This could be the reason why it fails the test when you change around the mains connections (configuration) in as much as it only needs some slight change that itself need not be related to the output, to highlight the very odd nature of unintentional (and unwanted) rectification of very low current signals around a few micro-amps at higher frequencies, as yours is. Also, the tester may only be expected to read ac voltages around 50/60 Hz and when confronted with stray voltages in the kilo-hertz, unless a true-RMS tester, it can not interpret correctly the values of the signals either.

Incidentally, if you want to test for leakage current at the aerial at any time, then the easiest way is by wrapping the insulated aerial in aluminium foil after say adding a coupling jelly to the foil. I have used simply ultrasonic jelly for this purpose as it firstly does the job well and secondly, unlike a salty paste, will not add a possible source of corrosion to the aerial, or the crocodile clips used for the test on the foil.

Lastly, I, like other readers, am very curious and interested to know how this aerial fits into the workings of the machine. I say this because for Cutting and Coagulation to be effective, a large amount of current has to flow in the patient circuit. This of course goes normally through the patient plate. But if there is only the "Ether' between the patient and the machine on the return path, there will not be the possibility for anything but very small radio-sized currents to flow. If you have now the technical description of this machine, I too would be very interested to receive a PDF of it. Thanks - Nick

Hi Nick,
Thanks for your very interesting comments, I don't have access to the tech manual yet.
The 'aerial' return electrode, as I understand it, must be in the form of a loop fed by twin cable, and is about the size of the normal split return electrode. The 'aerial' is placed in close proximity to the patient, even placed upon the surgical drapes.
The 'old' days of individual test instruments to test a device are long gone.
Personal question - are you ex Arborfield Med & Dent, my poor ageing brain recognises your name from somewhere.
regards
Pete

Pete, many thanks for the note however sorry to say I am not He from Arborfield. I used to work in Leicester, Tanzania, Malawi, Guatemala, Dublin, Jordan and now Saudi Arabia. Does that jog a few dying cells? Interesting about the aerial.