# Calibrating DMM's



## Speedskater (Oct 2, 2009)

_Unless you have a legal or contractual need, I don't see much of a point for DMM calibration. The following is a little test I did last February of the meters that I had handy. Most were near or better than 1 % even the $4 ones.
_
Using my Keithley 2000 as reference I checked the following units.

Keithley 2000 6½ digit, multi-meter. From about 2001 $1200.
Keithley 177 4½ digit, multi-meter. About 30 years old, currently $375.
Fluke 8020A 3½ digit, multi-meter. About 30 years old.
Radio Shack True RMS 3½ digit, multi-meter. Maybe 8 years old.
Kill-a-Watt P4400 3½ digit, plug-in-meter. About 1 year old.
M8303½ digit, multi-meter. Similar to the yellow Harbor Freight units.
From an outlet store $4. About 5 years old.
Harbor Freight Cen-tech DMM’s
Cen-tech 92020 3½ digit, multi-meter. $4. About 1 year old. Very noisy.
Cen-tech 95683 3½ digit, multi-meter. Under $20. 4 months old. w/current clamp.

None of the meters have been calibrated.

Model​ AC Voltage​ Error​ Keithley 2000
0126.00​ reference​ Keithley 177
125.75​ -0.2%​ Fluke 8020A
125.9​ -0.1%​ R/S 22-1758
124.6​ -1.1%​ Kill-a-Watt
125.6​ -0.3%​ M830
126.5​ +0.4%​ 92020
124.5​ -1.2%​ 95683
126.0​ 0.0%​ 


​ AC Accuracy of the Keithley 2000 when reading a 120V AC 60 Hz signal 
is calculated to be ±0.297V. Yep, not nearly as good as one might expect!
The accuracy takes a big hit when using the 750V range.
If we measure 99V on the 100V range then it” ±0.09V.

AC Accuracy of the Keithley 177 when reading a 120V AC 60 Hz signal 
is calculated to be ±1.03V.

The line voltage is a little high, because it was 55°F all night in Cleveland (it’s now 28°F). Not much power using activity in the neighborhood mid-day Friday.


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## Lone Crapshooter (Nov 8, 2008)

I think what would determine the need for calibration is what voltage level you are working with.
If you are doing electrical service work you really dont care if the motor is being fed by 479 or 480 volts. If you are working in a lab doing board level work yes it should be calibrated at least on a yearly interval. 
Anouther thing is the age of the meter and the cost of replacement . Transcat and Davis are proud of theri calibration service. Your meter is 11 years old it might not be worth the cost of calibration.
If you are doing process instrumentation and control work loop calibration equipment should be calibrated every year but it is more expensive than your standard DMM
LC


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## Zog (Apr 15, 2009)

Certified testing companies are required to have all of thier test equipment calibrated every year. Any one doing any real testing should do the same, most testing specs require the test equipment to be calibrated, the serial number and calibration date to be on the test form and a calibration certificate to be on file to be provided if necessary. 

Every company I have ever worked for has had all of thier meters calibrated annually, even if not required. I have seen about a 10-20% calibration failures over the years, and thats all quality equipment. 

I am shocked this is even an issue, do some poeple really not calibrate thier meters???


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## 480sparky (Sep 20, 2007)

Zog said:


> ..........I am shocked this is even an issue, do some poeple really not calibrate thier meters???


Or their torque wrenches?


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## paul d. (Jul 13, 2008)

i think most of us " test " our meters by actually using them. if i'm looking for 277v, does it matter if i get 276 or 278 ?? but there is a big difference between testing and measuring.


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## cdnelectrician (Mar 14, 2008)

I suppose you are all right, the most in depth stuff I get into is fire alarm, process controls and drives. It's time for a new meter anyways!

Just wanted to get an opinion on the matter...


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## NETA III Specialist (Jun 20, 2011)

*Calibration*

Currently in the process of opening a Test Equipment Calibration Lab and Rubber testing facility. Looking for input on resorces for calibration lab. Looked all over the internet and am unable to come up with what drives the Calibration standard for each piece of equipment. NIST is just a bunch of mumbo jumbo. Is There is no all inclusive reference to calibrating? Is it in the specs of the equipment as to what function and what standard I calibrate? Or is there a standard that covers all equipment in general?


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## zwodubber (Feb 24, 2011)

We send our PQ meters in every year as specified by the manufacturer. If we feel one has been abused, dropped, etc... It goes in before it's due


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## electricalperson (Jan 11, 2008)

how do they calibrate a meter?


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## ilikepez (Mar 24, 2011)

They have highly accurate reference sources. Special Zener diode circuits for instance for voltage references. They produce a variety of references over several ranges and check the meters readings against their reference. They then take the readings and chart the deviation for you. This information is tracked for each meter you calibrate, and if its out of the specification they adjust it. 

Some meters even of the same model will hold their calibration much better then others because of variations in materials and manufacturing.


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## MisterCMK (Jul 5, 2009)

What does calibration usually run for a meter?


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## farlsincharge (Dec 31, 2010)

Zog said:


> Certified testing companies are required to have all of thier test equipment calibrated every year. Any one doing any real testing should do the same, most testing specs require the test equipment to be calibrated, the serial number and calibration date to be on the test form and a calibration certificate to be on file to be provided if necessary.
> 
> Every company I have ever worked for has had all of thier meters calibrated annually, even if not required. I have seen about a 10-20% calibration failures over the years, and thats all quality equipment.
> 
> I am shocked this is even an issue, do some poeple really not calibrate thier meters???


I'm pretty sure I don't do any of the things you do.


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## zwodubber (Feb 24, 2011)

MisterCMK said:


> What does calibration usually run for a meter?


Dranetz is in the $2xx range and I am not sure about the Amprobe DMIII


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## MDShunk (Jan 7, 2007)

My day to day meters I don't have calibrated, but a certain few I do send out for calibration. Insurance work I always use a calibrated instrument, since I have to note that in the report. I always expect about 100 bucks per, unless repairs are needed.


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## brian john (Mar 11, 2007)

I have approximately 200-300 pieces of equipment, that are calibrated at least once a year, expensive, a pain, and necessary.

Some goes to the manufacture, the rest is calibrated by a local firm that offers calibration and repair services, they come to our shop and set up for a few days.


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## Jlarson (Jun 28, 2009)

Like Marc we don't bother with day to day instruments only the ones used for actual testing and PQ.


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## wptski (Jun 30, 2008)

MisterCMK said:


> What does calibration usually run for a meter?


I happened to just check what Fluke charges for calibration on a 87V and that was $100.


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