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EZstim II nerve stimulator functional test #73901
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tech84 Offline OP
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Hello all,

I have a nerve stimulator for repair and I am thinking how to do functional test(as a nerve stimulator). If I connect a 2k resistor( as seen in the operators manual image attached) between the output probes and see it on an oscilloscope. If I select 10mA output, I expect to see on oscilloscope a pulse with an amplitude of 20V( 10mA*2k)?. Please can someone indicate if this procedure is it good or not? or kindly otherwise indicate another way how to check the output of the unit please.

Thanks and all the best,
Saviour

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Re: EZstim II nerve stimulator functional test [Re: tech84] #73903
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Geoff Hannis Offline
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When testing stuff like this - as well as TENS units, and the like - I always used my trusty 1 K as a load. That way the Ohms Law calculation(s) are simpler!

Otherwise, if you have time, you might want to check outputs at other loads:- 500 ohms (good skin contact) and 5 K (poor skin contact), for example.

I wouldn't worry too much about amplitude (apart from recording it "for interest"). Far more important are the series of output waveforms that this unit can produce (see the Operator's Manual). See if you can reproduce the nice waveshapes given in the manual.

As long as you have a decent 'scope you should be OK. smile

Meanwhile here is an old paper that you may find interesting. There used to be some proprietary testers for nerve stimulators - no doubt there are some nice ones about these days.

One last tip:- always use fresh batteries! smile

As an aside, you might want to think about how the user is to be reassured that the nerve stimulator works! In my experience this has often been the real problem; you know, it works OK on your bench, but the anaesthetist et al is not convinced. It is critical that the stimulator functions correctly, in order that paralyzing drugs are administered in the correct dose over time. But these relatively simple hand-held devices are subject to daily physical abuse, and often malfunction. However, it is sometimes not readily apparent that they are malfunctioning. A project for you (and any others) who want to Do Something Useful, perhaps - that is, a simple tester for the staff to use.

Back in the Good Olde Days - when I used to come across many and various TENS units and nerve stimulators - for each type encountered I used to make a sketch of the testing set-up, record settings, and then make a sketch of the output waveform obtained on the 'scope; with a Filofax (anyone else remember them?) page for each example. Where possible (and for ease of comparison) I tried to use the same settings each time on the 'scope. I could then quickly decide if the next one tested was indeed a wrong 'un! I'm looking at the remnants now - it's amazing (well, perhaps not) how much those "square" (squareish) waveforms vary between manufacturers.

Re: EZstim II nerve stimulator functional test [Re: Geoff Hannis] #73905
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tech84 Offline OP
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Million Thanks!
I wish you and your family the best for New Year!

Last thing, can I roughly use ohms law as stated in my first post to know the current from voltage reading of the oscilloscope please.

saviour

Re: EZstim II nerve stimulator functional test [Re: tech84] #73906
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Geoff Hannis Offline
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Although Ohm's Law applies (as it always does), the stimulator produces pulse trains (so the duty cycle comes into play). I'm not sure how it decides what current to display; it may measure it internally, but I'm suspecting that it just displays according to programmed settings. You may need to adopt an attitude of "trial and error" and observe what is going on.

Clue:- does the current display change in a smooth fashion, or in steps? The manual mentions "constant current".

You might like to simply insert a multimeter into your test circuit(s) and see what current readings you obtain in series with the load. Who knows, they may be near enough to what the stimulator displays! But remember RMS (which is different for a square wave than for a sine wave, of course).

So it will be interesting to see how your measurements compare with the display on the stimulator ... and also, perhaps, over a range of different load resistances. You could then make up a table of stimulator settings versus meter current readings, and retain these for future reference. smile

Re: EZstim II nerve stimulator functional test [Re: tech84] #73907
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tech84 Offline OP
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Dear Geoff,


Again thankyou for your help, smile

I am going to try the setup shown on the paper you gave to me to be more accurate, ie with the shunt resistor(1 ohm) in series with 1k(with or without capacitor in parallel) with the oscilloscope , once done I will let you know with the results.


Goodnight
Saviour Muscat



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Re: EZstim II nerve stimulator functional test [Re: tech84] #73908
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Geoff Hannis Offline
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Sounds like you're getting serious, Saviour!

But yes; that looks like a sensible test setup - especially as regards current regulation. It will be interesting to see how you get on.

I'm hoping (or more accurately, assuming) that you have a dual-channel oscilloscope.

Enjoy your New Year Celebrations (one hour ahead of us here, I believe). smile

When I was out roaming around town this evening, it was noticeably quiet (pity about the noisy neighbours, though). Mild out, too. I might take a tea break around midnight.

Re: EZstim II nerve stimulator functional test [Re: tech84] #73913
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tech84 Offline OP
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Hello,

I tested the said equipment with the kind help of Geoff which I wish him gratitude :),


The aim was to see four pulse train across the shunt resistor(1 ohm) and also across the 1 k(ohm) with not much success (setup was with/without capacitor across the 1k) but I was able to see only like one square wave across 1k which I derived the current from it, the resultant calculation of current match with DUT selection current. I think that the oscilloscope wasn't powerful enough to see the correct signal, but with the result calculation obtained by testing conclude that probably the unit works properly.

Thanks very much
Saviour Muscat

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Re: EZstim II nerve stimulator functional test [Re: tech84] #73914
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Geoff Hannis Offline
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Geoff Hannis  Offline
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Well done. smile

Stange that you didn't get anything across the 1 ohm shunt. I would have expected a pulse similar to the one taken across the load (as Mason shows).

Lastly, did you get a chance to check out current using a multimeter? think


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