Author Topic: Help with new DMM  (Read 18969 times)

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Offline zorthgo

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Re: Help with new DMM
« Reply #25 on: July 09, 2013, 04:40:30 am »
@c4757p, your right, that is one of those pocket meters. They are convenient, because I just toss them in my electronics bin and take them to school (or wherever I am working on a project). Don't worry, I don't plan on doing anything with high voltage. I just want to work with low voltage electronics... you know, your average analog sensors feeding into a Pic, Ardunino, etc. You know, basic electronics!  :D But I think it's time I should get a decent DMM. (And I totally understand the Health care remark!)
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Offline Lightages

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Re: Help with new DMM
« Reply #26 on: July 09, 2013, 04:44:42 am »
Good Idea Fsck, for the second DMM I think I am getting the EXTECH EX430 as c4757p suggested!  :-DMM


Thanks for the help guys! Much appreciated!

I have a much different opinion of Extech EX series meters. They rather unreliably built. Parts falling out because they weren't soldered correctly, easily broken selector dials, etc. I seriously would never buy an Extech EX series meter. Please consider the Brymen BM869 and the BM257 if you want two meters, or the BM525 to have as an alternative. The BM525 does internal logging up to 20 times a second with a memory of up to 87000 points. Of course to read back all that you would need the data cable. The BM257 makes a nice compact rugged meter with the addition of a non-contact voltage detector to let you know if you have a live wire without touching it.

Or if you are willing to never use it on anything other than electronics then another consideration could be a Uni-T UT71D. It also has internal logging for a low price but it has some other poor qualities.

Search for reviews for all of these here, including the Extech EX series and you will learn quite a bit.
« Last Edit: July 09, 2013, 04:58:12 am by Lightages »
 

Offline zorthgo

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Re: Help with new DMM
« Reply #27 on: July 09, 2013, 04:52:55 am »
@Lightages, I know,  I probably should have waited a little bit more. But I already bought the Extech EX 430 on ebay (it was only $48). At that price, if it breaks, I can just get another! As long as it is accurate! ;)
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Offline zorthgo

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Re: Help with new DMM
« Reply #28 on: July 09, 2013, 04:54:19 am »
@IanB, you like everything to look right... You probably would die if you worked with the equipment I have right now! lol!

I am guessing it is the power supply that is showing the wrong reading.
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Offline IanB

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Re: Help with new DMM
« Reply #29 on: July 09, 2013, 04:54:25 am »
@IanB, now I get why you didn't mind you Radio Shack DMMs! After seeing the picture you will understand why I need a real DMM! ;)

Yeah, that's a $2.99 DMM. At some point there is a price to pay for cost cutting. Even so, such bargain basement meters can still be serviceable as long as you check them against a known reference before you use them:



We see here that 10.0072 V is between 10.00 and 10.01, so the lower resolution meters are undecided and they split the difference.

(Note: I adjust my meters to make them read that well. They won't necessarily do that right out of the box.)
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Offline zorthgo

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Re: Help with new DMM
« Reply #30 on: July 09, 2013, 04:59:00 am »
@IanB, now I get why you didn't mind you Radio Shack DMMs! After seeing the picture you will understand why I need a real DMM! ;)

Yeah, that's a $2.99 DMM. At some point there is a price to pay for cost cutting. Even so, such bargain basement meters can still be serviceable as long as you check them against a known reference before you use them:



We see here that 10.0072 V is between 10.00 and 10.01, so the lower resolution meters are undecided and they split the difference.

(Note: I adjust my meters to make them read that well. They won't necessarily do that right out of the box.)

You said you adjust the meters yourself. Are there any tutorials online that I can learn to calibrate them? Is it something that a beginner could do?
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Offline IanB

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Re: Help with new DMM
« Reply #31 on: July 09, 2013, 05:00:33 am »
(Note: I adjust my meters to make them read that well. They won't necessarily do that right out of the box.)

Also, I last adjusted all those meters at least a year ago. Even a $2.99 Harbor Freight special will hold its calibration without much drift once correctly adjusted. The main problem with the HF cheapies (and it's a big one) is the rotary switch. The contacts oxidize over time and make the meter reading go wild unless you turn the dial regularly to keep the contacts clean.
« Last Edit: July 09, 2013, 05:15:37 am by IanB »
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Offline IanB

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Re: Help with new DMM
« Reply #32 on: July 09, 2013, 05:11:41 am »
You said you adjust the meters yourself. Are there any tutorials online that I can learn to calibrate them? Is it something that a beginner could do?

Yes, adjusting inexpensive meters is easy and is something anyone can do. If you open them up you will usually find a trim pot inside marked "DC V" or something similar. You need a reliable voltage reference such as the DMMCheck or another meter of known accuracy. You just adjust the trim pot until the reading matches expectation. (Careful with the adjustment, it only needs tiny movements.)

The advantage of inexpensive meters is you can do this adjustment without much fear, whereas you wouldn't dare touch the adjustments on an expensive meter like a Fluke or an Agilent.

When you play with meters you will find that 3.5 digits of accuracy is stable and readily achieved. It's the 5th, 6th and more digits that start becoming a challenge. Luckily most inexpensive meters don't have so many digits to worry about, and neither do normal circuits care about such accuracy.
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Offline zorthgo

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Re: Help with new DMM
« Reply #33 on: July 09, 2013, 05:30:17 am »
@IanB, cool! Thanks for the instructions. I can't wait till I get the DMMs so I can mess with this one!  :-/O
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Offline IanB

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Re: Help with new DMM
« Reply #34 on: July 09, 2013, 05:34:16 am »
@IanB, cool! Thanks for the instructions. I can't wait till I get the DMMs so I can mess with this one!  :-/O

Note, I'm not suggesting you try to adjust a brand new meter away from its factory settings unless (a) you know the readings are inaccurate, and (b) you consider the meter expendable in the event you mess it up. I'm talking about inexpensive meters here.
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Offline zorthgo

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Re: Help with new DMM
« Reply #35 on: July 09, 2013, 05:37:01 am »
lol! I was talking about tinkering with my Radio Shack meter. I will leave the new ones alone for now! ;)
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Offline Lightages

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Re: Help with new DMM
« Reply #36 on: July 09, 2013, 05:38:54 am »
I would also recommend getting a DMM Check Plus from www.voltagestandard.com  It is well worth the investment.
 

Offline IanB

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Re: Help with new DMM
« Reply #37 on: July 09, 2013, 05:55:18 am »
@IanB, you like everything to look right... You probably would die if you worked with the equipment I have right now! lol!

I am guessing it is the power supply that is showing the wrong reading.

OK, 2.3 V vs 2.58 V. That's bad, about 10% off. Nothing should be that far out. Even basic meters should read within about 1% or so.

What is the power supply? Do you have a third reference to check against? A borrowed more accurate meter perhaps? You really need to know whether it is your DMM or the power supply that is wrong.
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Offline zorthgo

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Re: Help with new DMM
« Reply #38 on: July 09, 2013, 05:59:38 am »
Well, basically, the only option I have is to wait until my new meter/ DMM tester to arrive. Everyone I know are programmers.so nobody has a meter. Unless I take the power supply to school and measure it with one of the trektronix DMM that we have there! If it is the power supply is there any way I can adjust it?
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Offline IanB

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Re: Help with new DMM
« Reply #39 on: July 09, 2013, 05:59:57 am »
@IanB, Question... Did you make your own banana plug cables for you power supply? Where did you get the banana end clips? Do they work as well as the store bought ones? I need some cables fast would be cool to make them! ;)

Yes I make my own power supply patch cables. I use 14 AWG speaker cable as it is nice and flexible and has fat copper inside it for low resistance. Banana plugs and alligator clips come from my local Fry's. A bit more expensive than an online merchant, but I can examine them before I buy so I know exactly what I'm getting.

Soldering such items can be tricky, so expect a few retries before you get it right.
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Offline zorthgo

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Re: Help with new DMM
« Reply #40 on: July 09, 2013, 06:03:23 am »
Cool, I have 14 AWG speaker wire here at the house, and I'll look for banana plugs at my local Radio Shack (we don't have a Fry's here in Boca Raton). I'll take any excuse to fire up my soldering station! OH YEAH!
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Offline IanB

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Re: Help with new DMM
« Reply #41 on: July 09, 2013, 06:04:03 am »
Well, basically, the only option I have is to wait until my new meter/ DMM tester to arrive. Everyone I know are programmers.so nobody has a meter. Unless I take the power supply to school and measure it with one of the trektronix DMM that we have there! If it is the power supply is there any way I can adjust it?

I've no idea if the power supply can be adjusted. But usually it would not be worth trying. Just check the readings against a good DMM and make a note of the differences. Then when you set the power supply you can compensate for the error accordingly.
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Offline c4757p

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Re: Help with new DMM
« Reply #42 on: July 09, 2013, 06:22:44 am »
I had a similar one and it had easily accessible trimmers on the back of the display board.
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Offline IanB

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Re: Help with new DMM
« Reply #43 on: July 09, 2013, 03:01:22 pm »
Why do they put the temperature in Fahrenheit? Seems a bit random for a scientific instrument.

In America all temperatures are in Fahrenheit. (All measurements are in feet and inches and all weights are in pounds and ounces. You get used to it.)
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Offline Fsck

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Re: Help with new DMM
« Reply #44 on: July 10, 2013, 12:53:46 am »
Why do they put the temperature in Fahrenheit? Seems a bit random for a scientific instrument.

In America all temperatures are in Fahrenheit. (All measurements are in feet and inches and all weights are in pounds and ounces. You get used to it.)

Not if you're a scientist. :P Every american academic journal/paper/etc that I've ever read uses SI.
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Offline c4757p

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Re: Help with new DMM
« Reply #45 on: July 10, 2013, 01:02:00 am »
(All measurements are in feet and inches and all weights are in pounds and ounces. You get used to it.)

This "X and Y" thing is retarded. I had a good laugh back when my dad was remodeling our old house, and he'd always struggle with simple addition and subtraction of measurements in feet, inches and sixteenth-inches, and then he refused my suggestion to just measure everything in decimal inches because it'd be "too confusing". |O

The fact that we don't measure in feet, inches and bees' dicks shows that people can handle fractional inches. So why do they think they need this idiotic mishmash of units??

We do this everywhere, too. I also remember my mom scurrying around the house once looking for a tablespoon to measure with because a recipe called for "1 tablespoon plus 1 teaspoon". (Why there was none to be found in a kitchen is beyond me...) 1T + 1t = 4t....
« Last Edit: July 10, 2013, 01:06:44 am by c4757p »
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Offline zorthgo

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Re: Help with new DMM
« Reply #46 on: July 10, 2013, 01:02:55 am »
I agree with Fsck, In college we also use the SI unit. I am a CE major and have never used anything other then the SI unit in school.
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Offline zorthgo

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Re: Help with new DMM
« Reply #47 on: July 10, 2013, 01:22:09 am »
Hey IanB, I just couldn't wait until I got the DMM I bough online, so I went out and got one of the same DMM as you have on your picture. My question is, does it have a back light for the screen? I couldn't find anywhere to turn it on.
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Offline IanB

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Re: Help with new DMM
« Reply #48 on: July 10, 2013, 02:24:55 am »
Hey IanB, I just couldn't wait until I got the DMM I bough online, so I went out and got one of the same DMM as you have on your picture. My question is, does it have a back light for the screen? I couldn't find anywhere to turn it on.

You got the 22-812 with the PC interface? That's a nice meter.

It has no backlight, but I have never needed one for electronics. If my workbench is too dark to see the meter it is too dark to see what I'm doing...
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Offline ahnuts72

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Re: Help with new DMM
« Reply #49 on: July 10, 2013, 02:30:53 am »
Zorthgo no backlight I have 2 just like Ian's and I have no prob with them seem like solid meters of you recognize their limitations.

I also have 1 of the pocket meters
like yours as well.

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