DMM Tips and Tricks, Let's start a list.

[John_P_WI]

Everyone,

Last night I talked a little about the difference in Peak to Peak vs RMS voltage measurements on an oscilloscope vs a DMM. Reading through the various threads there seem to be some fundamentals lacking with test equipment use from the newer posters. How about we all pile on and make a list of tricks? We all have a lot test equipment tips and tricks accumulated over our "hobbyist career". Who knows, maybe it can be "sticky" material. Let's dedicate this one to DMMs, I will start another scope thread soon.

There are a large variety of "probes / leads" for DMMs. One of my favs is to use clip leads, I almost never use the regular leads any more. One of my favorite sets is the mini clips to banana from Pomona. The bananas are jacks allowing jumpering to another DMM for current measurements etc. More on this at a later time.

I use the larger Fluke clips with heavy leads for higher voltage / current measurements, although I find the silicone leads to tangle easily.

[img:800:450]http://i1148.photobucket.com/albums/o57 ... gkvhdq.jpg[/img]

Demonstration of the mini clips to measure capacitance:

[img:800:450]http://i1148.photobucket.com/albums/o57 ... gtixs8.jpg[/img]

Probably my favorite trick with the Pomona mini clips is to actually use the banana plug sockets for measuring components by slightly bending the leads and inserting them into the banana plugs. I especially use this when building pedals and measure many small components, besides the leads are then pre bent for forming to fit the pcb pads.

[img:450:800]http://i1148.photobucket.com/albums/o57 ... zvphic.jpg[/img]

Sometimes I get lazy and don't want to do the math to figure the frequency of the waveform shown on the analog scope. A simple solution is to use a BNC to banana cable and jump from the scope to the DMM input set on frequency of course.

[img:450:800]http://i1148.photobucket.com/albums/o57 ... cl2u50.jpg[/img]

One comment on cables, there is more than a difference in cost between the ebay cables and name brands such as Pomona. The cheaper banana plugs do not work well with cheaper meters - even BK. The Fluke sockets are deep enough that most any cables will work.

These are a few of my usual practices, what are yours? Let's get a list together and use our DMM's to their fullest.

[xtian]

Thanks, John. I need a set of those clip leads.

[xtian]

Uh oh, those Pomona mini-clips are only rated to 150V RMS DC. Not good for measuring HT.

[John_P_WI]

Yeah, that's why I showed the Fluke clips with a CAT III and CAT IV rating. Damn expensive with the required leads, nice for amp work - too big for bread boards. With the leads, the set is probably $60-$70.

http://en-us.fluke.com/products/all-acc ... l#features

and

http://www.mouser.com/Search/ProductDet ... y676-AC280

The Pomona mini clips are awesome for everything else.

[xtian]

Rats. Guess I'll just have to continue using my tongue.

[Structo]

Thanks John, never too old to learn!

Just remembering it is the hard part.

How did you connect the meter to the scope to show frequency?

[C Moore]

I'll ask a "dumb question".
I profess.....I have no idea what the difference is between:
RMS
and
True RMS
I have "heard" that True RMS can account for phase shift of an inductive load. If so, does that "normally" apply to what we do with guitar amps.?
What exactly IS True RMS.?
Thank You

[sluckey]

See this link...

http://en.wikipedia.org/wiki/True_RMS_converter

Or take a look at this 2 minute video...

https://www.youtube.com/watch?v=XUdRW0XgYQs

[C Moore]

Yeah...that is, kind of, what I thought.
I have 2 DMM.
My Amprobe was about 80 bux and my Extech was about 50.
Looking at them, and their manuals, it would appear that neither of them are "True RMS".
They are only used for tube amps, and basic stuff around the house, so it has not really been an issue.......not that I know of anyway...

[John_P_WI]

How did you connect the meter to the scope to show frequency?

Hi Tom,

The signal generator is connected to channel one of the scope via a BNC cable to a BNC Tee. The other side of the Tee is connected to the circuit under test via a BNC / coax / to mini clips (Pomona).

Being that the signal generator is connected to channel one and my scope has a channel one output, I simply connect a BNC to banana from the output to the DMM. Many scopes will have a similar output of some sort that can be used.

[img:450:800]http://i1148.photobucket.com/albums/o57 ... 9mbo04.jpg[/img]

[img:300:185]https://www.picotech.com/images/uploads ... 29-web.jpg[/img]

[John_P_WI]

For you guys who have "80" series Fluke DMMs (83, 85, 87), here is a quick way to tell if they are operational and in cal.

Set the DMM to "ohms" and insert the red test lead into the top part of the ma ua jack as shown. The closer the reading to 1k ohm the better. This is a good quick test for anyone interested in purchasing a used meter.

As you can see below, my 20 year old heavily used Fluke is still right on the money!

[img:360:640]http://i1148.photobucket.com/albums/o57 ... altru8.jpg[/img]

[Colossal]

Great tip John. My 87V measured 1.000k.

[John_P_WI]

Great tip John. My 87V measured 1.000k.

Spot On!

[kevania]

As an amateur this thread was very interesting. The kind of tips that help a new guy. I hope it gets picked up again before the end of the year.

My tip is "Always cHeck the Batteries in cheaper units!"

My cheapo I just died. Raising cash for a Fluke now....

[Ken Moon]

Here's a tip that seems totally obvious, but you'd be surprised how many meters are blown this way:

Don't measure the AC line when in OHMs mode.

I know from which I speak - many years ago I worked at Fluke, and had a quota to fix 5 DMMs a day

[img:768:1024]http://i514.photobucket.com/albums/t346 ... 150046.jpg[/img]