Meter Calibration - OEM or Metrology Lab

As 1audio already wrote, a calibration is nothing more than a check against factory specs. You'll get back the meter unopened, with a pass/fail certificate. You need to supply the factory specifications along with the instrument.
Adjusting a meter to factory specs is a service task. If it goes out of specs sometimes the cause is a faulty component.
Referring to different DMMs showing different AC for non-sinusoidal waveforms: use a True RMS multimeter.
See post 14. Headed to Metrology with cal instructions and specs. I'll get a full report when finished. Getting specs at various AC frequencies too.
 
We had a Fluke 8920A true rms meter. The thing was super wideband. It cleverly used a thermally isolated bolometer for rms measurements. The signal would heat up a resistor (50 Ohms?) and on the same substrate, another resistor would be heated up with a known dc current. Somehow the thermal gradient is sensed and feedback sets it to zero. The dc power is now the same as the rms of the signal. Anyway - I think that is how it worked.
 
Let me clear up a fundamental common misunderstanding about "calibration". It does not mean "adjust", it means "checking" and in this verifying if the device meets its specifications.
thanks for this. what is it called and where do you go to get an instrument opened and the service manual procedures are applied to adjust it back into spec using the recommended or equivalent supporting instruments No repairs or mods, so not just yes/no in spec or off by x or y but actually try to bring into spec. Does such a service even exist for discontinued oldies like HP or others.
 

1audio

Member
Paid Member
2004-03-24 5:16 am
SF Bay Area
This may help explain the variations possible with calibration services: https://www.tek.com/en/services/cal...ogle&utm_term=accredited calibration services In may cases they can and will adjust. In a system where real quality management is important you will want the as received and as returned report so you know if you were shipping bad product. But the full service can cost anywhere from $80 for a simple closed case automated calibration ( Fluke 8845) to $5K for a reference standard (Fluke 792) AC calibration. (https://www.custom-cal.com/Calibration_Price_List.aspx?kn=218&m=FLUKE_Calibration_Price).
 
Just a quick follow-up. Meters back from calibration lab with documentation showing pre and post measurement values and tolerance. One meter was out DC volts just in one range and another had an AC value off somewhere. Dialed in now. They follow the vendor's specification when it comes to AC values and what frequencies for cal.

They also cal / check frequency, Ohms, current and the handheld has capacitance and temp.
 

HalFoster

Member
2014-12-21 12:06 pm
For accuracy and affordability I would recommend a HP 3455A or 3456A - they can be found for $200 - $300 and the adjustments (if any are even needed) can be done easily. For the most part any that I have gotten are well within spec even after the last cal. being 15+ years ago. Or, for a newer model, a 34401A for a little more money.

Hal
 

HalFoster

Member
2014-12-21 12:06 pm
I just got a 3455A a couple of days ago and all it needed was the digital side bulk filter caps replaced - the last cal sticker on it was from 1987 and it was only off 50uV at 10VDC and within spec for the entire DC range. Haven't checked AC and ohms yet but would be surprised if they were not just as accurate.

Hal
 

HalFoster

Member
2014-12-21 12:06 pm
It's been mentioned already I believe, but keep in mind that sending a meter for calibration is not the same as having it adjusted to specifications - it will only (if you purchase the "with data" option) tell you what reading it has for each expected value. In a professional setting this usually just serves to say "your instrument is still within specs" with a certificate of proof. It is fairly unusual for a meter to actually be out of specifications - if it is, then negotiations with the cal lab to make adjustments can be done (pricy) or, often, a replacement is bought. For the individual the results can (even if out of spec) be used to make an table of correction values - for this range, multiply the reading by X to get the accurate result. This can often be done for free by having someone with a known accurate instrument do the same thing as the cal lab. At minimum the standard needs to be 4X as accurate but an order of magnitude is much better.

Hal
 

Jonpaul

Member
2013-02-09 9:20 pm
Paris
Bonjour à tous

just seeing this now..

Had worked at Julie Research in 1960s and went through cal on various scopes and meters.

The OP should info us his required accuracy and ranges used.

We can discuss cal option and possibly other meters.

The Fluke TRMS mentioned are dc..20 MHZ 3.5 dig use a heater/sensor IC in feedback loop.

Very accurate great peak ratio, but 1980s so may be hard to restore...we have 3..4!

Bon courage

Jon
 
I'm working on a DIY project that requires accurate AC and mV AC measurements. In 2016, I sent my HP 3400A and another HP400 series meter for official calibration to a Metrology lab in the North East. Got the full reports, cal stickers and Void if removed stickers over screws. Wonderful. My handheld DMM and 4 1/2 digit bench top meters do not match each other and do not closely match the HP meters. Yes, all have been on for hours, etc.

So I'm debating where to send the digital meters. The Metrology lab said send them and they will most likely be able to calibrate them. However, I hate to waste shipping dollars if they can't. My meters are BK Precision 2831E and Extech MP530 (a Fluke 87 knockoff). BK wants quite a bit of money to cal and then return. I'm not getting a NIST cal, just a regular cal with documentation. Still pricey. I called Extech, which is now part of FLIR and they are not sure they handle the old product lines. I asked them to provide the calibration documentation so I can forward it to the Metrology lab. I am waiting for tier 2 support to respond to that request. I don't have good hopes on them releasing the info.

Any opinions about OEM vs Metrology lab?

Before anyone craps on the Extech (fluke knockoff), I refuse to buy Fluke products. In my industry, they have totally ruined the test equipment products by buying up other vendors, end of life their products, and then force the new over-priced & unreliable crap down our throats. It was so bad, a $20K analyzer kept loosing cal settings and was returned 3 times in a 12 month period. They refused to send a new unit in exchange for something that was in for service more than in my hands. When we spend $100K on test equipment, I now support the other vendors as much as possible. And their products are as good or better than Fluke. OK, off my soap box.
In my experience, you pay extra for Keysight but they might be better than your local lab. We had some U1723A that passed cal with a local group but were acting funny at certain settings. Sent to Keysight and they replaced the board.
 
Before anyone craps on the Extech (fluke knockoff), I refuse to buy Fluke products. In my industry, they have totally ruined the test equipment products by buying up other vendors, end of life their products, and then force the new over-priced & unreliable crap down our throats. It was so bad, a $20K analyzer kept loosing cal settings and was returned 3 times in a 12 month period. They refused to send a new unit in exchange for something that was in for service more than in my hands. When we spend $100K on test equipment, I now support the other vendors as much as possible. And their products are as good or better than Fluke. OK, off my soap box.
I can relate to your fluke experiences. Fluke wants the cream of the crop customers, who have limitless budgets, and really don't care about price! Since I've worked on a lot of metrology equipment, I usually do my own service, and just purchase the parts. But I had 2 Fluke 732B DC standards that had blown line filters, which was causing the trans secondary to spike when energized, which was tripping the crowbar.

The transformer assembly is riveted together, and Fluke wants over $1,000 for it. So, I drilled the rivets, pulled the Schaffner power entry module, put in a $30.00 replacement, tapped the rivet holes, and screwed it back together (2 hours for the first one, 45min for the 2nd). I wrote to Fortive, Fluke's parent company, telling the CEO that I will gladly purchase parts, if they cost me less than to repair the failed one! Never heard anything back!

So, I think Fluke is run by bottom-line types totally detatched from the purpose of the products. But just wait until the crest of the wave of reputation they're riding on comes crashing into the shore of pissed-off buyers willing to look elsewhere! For me, since I use Precision DC standards, Fluke is the only game in town, by a long shot, so I'm stuck there, and their electrical calibration equipment is still pretty top notch, they're just becoming a scummy company!




I'm working on a DIY project that requires accurate AC and mV AC measurements. In 2016, I sent my HP 3400A and another HP400 series meter for official calibration to a Metrology lab in the North East. Got the full reports, cal stickers and Void if removed stickers over screws. Wonderful. My handheld DMM and 4 1/2 digit bench top meters do not match each other and do not closely match the HP meters. Yes, all have been on for hours, etc.

So I'm debating where to send the digital meters. The Metrology lab said send them and they will most likely be able to calibrate them. However, I hate to waste shipping dollars if they can't. My meters are BK Precision 2831E and Extech MP530 (a Fluke 87 knockoff). BK wants quite a bit of money to cal and then return. I'm not getting a NIST cal, just a regular cal with documentation. Still pricey. I called Extech, which is now part of FLIR and they are not sure they handle the old product lines. I asked them to provide the calibration documentation so I can forward it to the Metrology lab. I am waiting for tier 2 support to respond to that request. I don't have good hopes on them releasing the info.

Any opinions about OEM vs Metrology lab?

Before anyone craps on the Extech (fluke knockoff), I refuse to buy Fluke products. In my industry, they have totally ruined the test equipment products by buying up other vendors, end of life their products, and then force the new over-priced & unreliable crap down our throats. It was so bad, a $20K analyzer kept loosing cal settings and was returned 3 times in a 12 month period. They refused to send a new unit in exchange for something that was in for service more than in my hands. When we spend $100K on test equipment, I now support the other vendors as much as possible. And their products are as good or better than Fluke. OK, off my soap box.