How to use a DVM to check your magneto.....

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40TPI
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How to use a DVM to check your magneto.....

Post by 40TPI »

Fluke are a long established digital voltmeter ( DVM ) manufacturer so it is no surprise that they had their marketing people write up an application note using their products for testing outboard ignition systems. And it is quite applicable in many ways to our Marston, Villiers and Wipac magneto ignition systems. When reading this application note bear in mind that our primary resistances are around 0.1 Ohm and our secondaries are around 3,750 Ohm (3.75kOhm).

http://assets.fluke.com/appnotes/electr ... 271b_u.pdf

Might save the regulars some finger wear when answering the never ending ignition questions from new members....... :)

The attention to addressing the target audience is also very good. This note was written many decades after electrical and electrical engineers had moved from jars and condensers and settled on capacitors but the editors kept to "condenser" for the spanner people ........ :wink:

Peter
Last edited by 40TPI on Wed Jan 19, 2011 10:29 am, edited 1 time in total.
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Re: How to use a DVM to check your magneto.....

Post by Collector Inspector »

Yep, DVMs are really good, use many different types in my line of work.

Old Dear Ignitions and some designs of Impedence feedback control circuits do sometimes confuse any Digital Device.

Sometimes, the only real truth in testing can only be collected by an AM.
19012011055.jpg
An AM, like the one above actually tests extra data over a general spec DGM......Thing is, you have to read the instructions and wear glasses. Very real readings but.

Expect to pay Aus$200 for a good device.

Regards
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Re: How to use a DVM to check your magneto.....

Post by 40TPI »

Apologies to anyone trying and failing to download the Fluke link last night. (My fault entirely. I missed the first "h" when cutting and pasting the link; now fixed.)

Along with the approximate resistance values for our Villiers and Wipac coils I should have also pointed out that a flywheel puller should not be used to remove the vast majority of Seagull flywheels. ( Only use a puller, and then only the internal threaded type, on ancient Marston/SD models)

To be clear I do not own any stock in Fluke however it is obvious they were hoping to influence people to buy their products for this application! (They wrote other marine electrical trouble shooting guides if you care to search....)

This was posted to give people confidence to tackle basic electrical trouble shooting on our simple magnetos. It was not an overt recommendation of DVM technology over traditional analogue and to suggest that only analogue meters can give a correct measurement in all situations isn't entirely helpful when we are trying to enable people to tackle this type of work with confidence. I can't imagine what measurement problems you refer to when making the trouble shooting measurements in the application note or other ignition problems with a DVM . Can you explain please?


Peter
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Re: How to use a DVM to check your magneto.....

Post by Collector Inspector »

Chill Dude!

Done before eh?

B
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Re: How to use a DVM to check your magneto.....

Post by 40TPI »

Hi Bruce, I'm perfectly chilled! .....................Just relaxing while you explain the problems with a DVM not telling the "real truth" like an analogue meter when it comes to making those resistance measurements in the Fluke application note. I'm hoping we can get the explanation out to help those readers who are reading this thread and are now fired up to try and sort their ignitions but are now suddenly caught deciding whether they ought to buy a DVM or analogue meter!!

Then we can move on to the other measurement problems you've had with DVMs not telling you the "real truth"!


Peter
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Re: How to use a DVM to check your magneto.....

Post by Hugz »

Excellent article. I note that Ebay is flooded with Fluke meters from China/HongKong. I assume these are counterfeit??
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Re: How to use a DVM to check your magneto.....

Post by Horsley-Anarak »

Better get my AVO out :wink:

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Re: How to use a DVM to check your magneto.....

Post by 40TPI »

Well , not really, the AVO 8 in all guises, does not match a Taylor Instruments Model 101 . Probably the best ever large scale analogue meter at 100kOhm/V. AVO had the Model 7 which was arguably the equivalent in terms of low volts drop analogue ammeter.

Think Bruce must have gone fishing.....................now he must be really chilled :wink:

Got to be lunchy/tinny times out there by now?




Peter
Last edited by 40TPI on Thu Jan 20, 2011 1:31 pm, edited 1 time in total.
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Re: How to use a DVM to check your magneto.....

Post by Collector Inspector »

AVO! Ahh, now someone is getting out the big guns.........never tried that with an old coil just in case, too over the top and oops! Really good or was maybe another 1000hrs left with Ano Meter.

I like that thought.........Try that next really dodgy back dodgy parts box coil I will.......... :twisted:

I will just sit back, have a couple of tinnies and see how Perths' latest fires are going on the net before doing digital vses anolog meter procedures for old ignition systems. As well as coils there is the ANO test for points and condensers remember them?

Also, please consider sparkplugs.................Resistor ones............Inductive Resister ones.............They have a value to be measured from the factory yeh? A value that provides feedback to a particular digital ignition system yeh?

What meter would anyone use to check these sparkplugs then...............DMM?..............and the reading is what?

Love this, hate the fires over here while the East goes Under! Silly Climate but NOT a change as espounded by our greens down under..........G but havnt they made some stupid comments lately?

Peter, REALLY GOOD lead in Mate!

8)

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