MultiMeters

[JOEX]

The manual recommends a digital multimeter that has minimum internal impedance of 10M ohms/DCV for testing certain components.

(Meters with differing impedance will not display accurate measurements).

There is also an adapter required for some of the testing (Kowa Seiki p/n KEK-54-9-B is one they suggest).

How do I tell what the internal impedance is of the multi meter and how imortant is it? Is the adapter really neccessary?

[Bush0102]

first off, what are you testing?

[Quad18star]

Where's Wilkin when you need him !!! :p

[JOEX]

Originally posted by Bush0102
first off, what are you testing?
Probably everything on the quad:ermm:

The manual recommends those items to test the ignition coil, ignition pulse generator and exciter coil.

The adapter is call a peak voltage adapter.


Where's Wilkin when you need him !!!
Yea, I think this is his department:p

[sly400ex]

Originally posted by JOEX
The manual recommends a digital multimeter that has minimum internal impedance of 10M ohms/DCV for testing certain components.

(Meters with differing impedance will not display accurate measurements).

There is also an adapter required for some of the testing (Kowa Seiki p/n KEK-54-9-B is one they suggest).

How do I tell what the internal impedance is of the multi meter and how imortant is it? Is the adapter really neccessary?

Well, I'm not a Electrical Engineer by any means, but you should be able to tell your meters resistance from the manual. I'm looking at my Craftsman it good down to 40M ohms, so it's plenty. DCV, the DC voltage meter portion, is used because quads run on a 12 V direct current electrical system. Just about any decent meter out there should meet your requirements.

Hope this helps!:)

[Rastus]

^^^^^ What he said. About any decent meter will do.

just jold your probes together, if they read 0 then it should test the resistance of a circut just fine..

[MOFO]

Get yourself a good Fluke and call it a day. Thats all I've ever used...

The internal resistance is used to "absorb" the electricity - Its been awhile since I've dealt with this stuff, but I did know the exact answer years ago...I believe this is how the meter works.

It applies a known DC voltage into the circuit. It then internally measures how much voltage is being "absorbed" by the internal resistance, then it takes that figure and calculates the resistance of your circuit.

Anyways, I believe its one of the main factors in how accurate the meter will be.

Like I said, buy it once... get a Fluke. :cool:

[smr]

This is really not much of a problem anymore. There was a time when digital meters first came out that you would have this problem. The resistance was so high to avoid feed back from the digital display. Like MOFO said..buy a good meter. Fluke is one of the best and you will have no problems. Simson analog is the best for checking electronics but I dought you want to spend that much money.

[Woodsrider]

Get a Fluke. A Fluke 78 to be exact, it will do everything you need to test your quad. Tach, dwell, min/max reading. Its the chit:macho Fluke 78 (http://us.fluke.com/usen/products/Fluke+78.htm?catalog_name=FlukeUnitedStates&Category=AUTO(FlukeProducts))
Platt electric carries Fluke, as well as Grainger, and Allied electronics in Beaverton.

[wilkin250r]

Originally posted by Quad18star
Where's Wilkin when you need him !!! :p

I get on mostly in the morning, I rarely have a chance to get on during the evening.




I can certainly type a huge post about differences in internal resistance, what it does, why it's important, and what would happen if you had less than 10M ohm (10 million ohm) resistance. But I'm firmly convinced that nobody reads them anyways, so I'll give you the short version.

It has nothing to do with feedback from the display, and isn't directly related to the accuracy of the meter, but rather the accuracy of your measurement when you connect your meter to your circuit.

Resistance is just like it sounds, it resists electrical energy. Therefore, a very high resistance like 10 million ohms will have very little power going through it when you connect it to a test circuit. You don't want your meter to change your circuit when it gets connected, a high resistance makes your meter almost invisible to your circuit, giving you an accurate measurement.

By comparison, if your meter had only 1M ohm of resistance, it would actually pull 10 times more power through it, and all that extra power is coming from your test circuit, and it will change how the circuit behaves. Imagine trying to measure the speed of a small airplane by opening a parachute on the back. The parachute has a very high wind resistance, and will slow the plane down, so are you really measuring the true speed? You don't want your meter to load down your circuit and change what you are trying to measure.

[wilkin250r]

So, on the original question, and a more lengthy explanation because I know that Joe will read the whole thing.

Joe, honestly, you don't need to worry about internal resistance. I wouldn't trust a cheap meter you get from the $1.99 bin, but almost any decent digital meter nowadays has at least 10M of internal resistance. In reality, even if it only has 5M, you're readings won't be THAT far off.

However, a peak voltage adapter probably IS necessary. A digital meter will give you an RMS value (Root Mean Square), not the peak value. The peak value is different.

For example, you probably know that your house is wired with 120V, right? You can measure it with the AC setting on your meter, it will measure somewhere between 110V and 120V. However, that is the RMS level, the PEAK is actually somewhere around 170-200 volts!!

This is very critical if you're troubleshooting your ignition.

Not only that, but digital multimeters typically have a response time somewhere around 1/2 second, but your ignition pulse is somewhere around 0.0001 seconds. Your meter is not fast enough to give you an instant value. That is why you need the adaptor, to HOLD that peak voltage value until your meter can read and display it.

Now, there are ways around this if needed. How much is the peak voltage adapter? If it's terribly expensive, I can easily show you how to build a cheap one yourself.

[JOEX]

Thanks for the info! You guys rock:cool:

The Fluke 78 sure looks nice but the MSRP is $299.95:eek2:

Are the $20-30 ones decent or should I go up more?

The adapter at one place was around $26 not too bad I guess.

[wilkin250r]

For $26, I'd pick up the adapter. I couldn't design one for less than $10.

Now that I think more about it, I think most of the hand-held multimeters are on the order of 2Mohm resistance. However, I honestly don't think it will throw your measurements too far off. If your actual voltage is 207V, but you're only reading 199V, you don't really care. You're more concerned whether it's working or not, rather than being dead-on absolutely accurate.

[wilkin250r]

In fact, if you CAN'T find an input resistance (or input impedance), you can assume it's on the order of 2-5Mohm, and this would be typical of meters in the $20-$30 range.

Anything that is 10Mohm or above will be labeled and specified as such.

I have a 10Mohm meter, but that's because I'm an Engineer and a nerd. Let's be realistic, you don't need to spend $150 in test equipment that you will never use again.

[JOEX]

I picked up a couple of them this week... What was available locally....

One has a resistance OHMS of 2M ohms +/- .75%

The other:
+/- .8%rdg +2 dgts @ range= 20K ohms, resolution = 10 ohms
&
+/- 1%rdg +2 dgts @ range= 2000K ohms, resolution = 1K ohms

I'm taking at least one back. Should I take them both back and get something a little better or will one of these be good enough?

[wilkin250r]

What specification are you reading?

This one...:

+/- .8%rdg +2 dgts @ range= 20K ohms, resolution = 10 ohms
&
+/- 1%rdg +2 dgts @ range= 2000K ohms, resolution = 1K ohms


...looks more like an description of capabilities, not internal impedance. This would be an description about the abilities of the meter, the total resistance that it can measure accurately. It would have nothing to do with internal impedance.

I'm out for the day, I'll try to get on tomorrow (probably afternoon-ish) to try to help you out. Give me the manufacturers and model numbers of the meters you bought, and I'll try to look up the specs and make sense of it.

[JOEX]

Originally posted by wilkin250r
What specification are you reading?

This one...:

+/- .8%rdg +2 dgts @ range= 20K ohms, resolution = 10 ohms
&
+/- 1%rdg +2 dgts @ range= 2000K ohms, resolution = 1K ohms


...looks more like an description of capabilities, not internal impedance. This would be an description about the abilities of the meter, the total resistance that it can measure accurately. It would have nothing to do with internal impedance.

I'm out for the day, I'll try to get on tomorrow (probably afternoon-ish) to try to help you out. Give me the manufacturers and model numbers of the meters you bought, and I'll try to look up the specs and make sense of it.
Those are the accuracy specs in the instruction manual for an Actron (http://www.actron.com/product_detail.php?pid=16157) CP7672

The other is a Gardnerbender (http://www.gardnerbender.com/) GDT-190A.

I'll pay a few more dollars for a better meter if it's worth it but i'm thinking about getting a welder so those $100 meters messin' with the budget;)

[Woodsrider]

Originally posted by wilkin250r
I have a 10Mohm meter, but that's because I'm an Engineer and a nerd. Let's be realistic, you don't need to spend $150 in test equipment that you will never use again.

For the most part I agree with this statement. But anyone who tinkers will get a lot of use out of a meter, and once you learn to trust it and use it right, it can save you a ton of money. LOL maybe a $300 meter is a little much for the tinkerer, but really, how good is a $20 meter for automotive diagnostics? I have a fluke 23, you can get it(its superseeded modle) for about $130 on sale, and as a mechanic it suited me fine for the last 12 years.

[wilkin250r]

Ok, so I didn't get a chance to hop on over the weekend.

Joe, the specifications you were are looking at are incorrect. Those specifications are the capabilities of the meter, the ranges it is able to measure accurately. It has nothing at all to do with internal impedance.

I checked the specs on the models you listed, and neither of them list an internal impedance, which means they are probably around 2M ohm.

You are going to be looking for very specific wording. Anything that says "Range" or "ohms" is most likely a list of capabilities, which is not the specification you are looking for.

You want to look specifically for "Input Impedance", "Input Resistance", "Internal Impedance" or "Internal Resistance". Any other wording, and it's most likely not the specification you are looking for.

I'm trying to get some more information right now.