Here's a reason why you should not buy a cheap DMM. The input filter in cheap meters easily gets confused and attenuates the signal, and worse than that, the amount of attenuation is unpredictable so you have no way to know the real measurement!
To demonstrate, I'll use a cheap meter (about $35) and an expensive meter (about $80) to measure the normal AC line.

So far so good, right? That's because they're measuring an almost pure sine wave.
But measure the UPS output and look what happens!

That's because they're measuring a square wave, which confuses the input filter in the cheap meter. The expensive meter has better input filters that are not confused by high frequencies in the signal being measured.
This inaccuracy is confusing at best and dangerous at worst. A cheap meter can easily cost you a lot in the long run!

I'm lucky, I have an expensive meter and the company I work for pays to have it calibrated on a yearly basis.

That is precisely why I shopped eBay til I found a good Fluke DMM.
Thanks for sharing.

Quote: Originally Posted by vf1000ride I'm lucky, I have an expensive meter and the company I work for pays to have it calibrated on a yearly basis.

Hey have your company use mine for their calibrations!!! Analytical Instrument Repair and Instrument Calibration - Moyer Instruments, Inc.

LOL Always trying to get new clients!

I vote STICKY - I learned more in four posts than I did some quarters I was at college.
-MF

Quote: Originally Posted by Monsignor Funkibut I vote STICKY - I learned more in four posts than I did some quarters I was at college. -MF

Were those the quarters you partied too much or just did a brain dump?

Stickified, but moved to a more appropriate forum (Hardware Advice Corner)

Most problems Inside a multimeter when measuring AC happen in the AC rectification section of the multiplier (which is a diode rectifier and some other circuitry). because the meter was cheap, 5% tolerance resistors and 1.4 to 2V diodes were used. The good ones probably use <1% tolerance resistors and .3 to .7V diodes inside the meter, which is why they cost more.

The A/D converter might also have more bits, or sample at a higher rate in the more expensive meter. This would effect the reading, as would the tolerance on ALL components effect drift in reading.

However, There is still the possiblity that the UPS Had some losses in its own network, BUT they would be very little as noticed in the AC output. However, they are also not measuring a square wave, but a modified square wave. It has the shape of a sine wave, but it has square waves in it (think stair cases).

, I had to devulge into the technical stuff for those who are technical or wanted to know random information.

Note: Those are voltage Drops of the diodes.

Many things output more complex signals than a multimeter can handle ( I too have a very nice Fluke) Anyone serious about electronics work needs a good oscilloscope too. Good info though.

Quote: Originally Posted by thedemonxanth Many things output more complex signals than a multimeter can handle ( I too have a very nice Fluke) Anyone serious about electronics work needs a good oscilloscope too. Good info though.

Very true, I am still trying to find a decent o-scope for relatively cheap.

Quote: Originally Posted by thedemonxanth Many things output more complex signals than a multimeter can handle ( I too have a very nice Fluke) Anyone serious about electronics work needs a good oscilloscope too. Good info though.

Or a data logger/ O-scope.
Data Acquisition Starter Kit Replaces Chart Recorder

Another meter worth trying is a Analog meter, the only error in a analog meter is human error.

My first O-scope was a buffer circuit connected to my sound card and a program called xoscope. YOu'd be surprised what you can do with just that. I also have an old radioshack probscope somewhere. If you want to score some sweet gear go to school auctions.

Analog meters are great for pulse and trend spotting, but a DMM with a bar graph works pretty well too.

Analog meters are certainly great for some things..but like most people these days, we are realy lazy and prefer the "Digital Readout" so we can see an exact number without having to fuss reading those little scale lines...lol

Great thread!

Quote: Originally Posted by thedemonxanth My first O-scope was a buffer circuit connected to my sound card and a program called xoscope. YOu'd be surprised what you can do with just that. I also have an old radioshack probscope somewhere. If you want to score some sweet gear go to school auctions. Analog meters are great for pulse and trend spotting, but a DMM with a bar graph works pretty well too.

Not just laziness but have you ever tried to read an analog meter accuratley in less than favorable lighting conditions? Pain, sparks, swearing, and a smell not unlike sauteed pork can result.

Quote: Another meter worth trying is a Analog meter, the only error in a analog meter is human error.

Not so. A purely analog meter I tried had the same problem. A DSP-based meter is needed to correctly measure a square wave. (My meter has a sampling rate around 40kHz (about 1% error at 400Hz) or so, which is plenty for most uses.)