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 Post subject: Meter Calibrator, who has one?
PostPosted: May Wed 26, 2021 12:37 pm 
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Location: Liberty, Missouri
Reading Steve's post about resistance Standards, got me wondering who among all of us here, have calibration equipment.

I have two, an OLD 1968 fluke 760A, that was capable of up to 0.05% accuracy when calibrated, providing AC/DC Volts from one millivolt to 1000 Volts, AC/DC current from 1uA to 10A, as well as Ohms from 1 to 10Megs in 1 Ohm steps. According to my HP3456A its still within a Half Percent.

Then again they could both be off quite a bit and just happen to agree. :wink: Click the pic for gory details.

Image

and my other is a little HP-6920B.

Image

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Wed 26, 2021 1:15 pm 
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Joined: Mar Thu 12, 2009 2:20 am
Posts: 1603
Location: Dayton, OH
I've a Dowty RFL 829M sitting on a shelf.

Either its not working, or *all* of my meters are wildly off at the higher voltage ranges. I'm more inclined to suspect the Dowty is bad, at least I have the service manual. (Its been scanned, and at the usual sites.)

Its supposed to do AC/DC @ 1100V & 2A (not simultaneously - heh) and contain a few resistance standards.

This isn't mine, but was the only convenient picture I could find: https://www.youtube.com/watch?v=iuDZ_3jCO30

David

Edit: I should add I have a DMMCheckPlus floating around as well.


Last edited by dholland on May Wed 26, 2021 1:44 pm, edited 1 time in total.

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Wed 26, 2021 1:29 pm 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 5097
Location: Melbourne, Florida
My voltage calibration setup is a little gizmo consisting of a ten-tun pot and a 9V battery. I also have a similar unit run from the AC line that goes up to 500 V. Both are set using a DMM.

My resistance standard is a little box with rotary switch and some 1% resistors that were checked with a bench DMM at my old company. The exact readings were recorded on the back.

This stuff is plenty good enough for VTVM's or anything else I'm likely to run into.

RRM


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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Wed 26, 2021 2:26 pm 
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Joined: Mar Sat 25, 2017 3:44 am
Posts: 141
Location: Kennesaw, GA 30152
I recently acquired a Fluke 5101B that is very accurate. I also have a Fluke 8840A/AF DMM I had calibrated so between the two I can get most meters back in calibration.
As a side note, if anyone is local to the Atlanta area I'd be more than happy to check/calibrate your meters. Send me a PM.


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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Wed 26, 2021 2:40 pm 
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Location: Roanoke, VA
I own a 4-1/2 digit Keithley true-RMS DMM. It goes to the cal lab annually, and serves as a reference for my other meters.

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Wed 26, 2021 3:25 pm 
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Joined: Dec Sat 28, 2019 4:18 pm
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Location: Corinth, TX
That is one of the few things I really miss after retirement: access to a roomful of lab calibrated equipment.

John


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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 12:23 am 
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I acquired an HP 6920b from a forum member quite some time ago. I really don't use it anymore. I decided my DMM was close enough to use as a standard to calibrate VTVM's and VOM's. I can check it occasionally by selecting some high precision resistors with the DER-EE5000, and then using those as a voltage divider to get voltages and currents accurate enough so that my DMM can be used as a calibration standard for anything I'm likely to need.

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 1:47 am 
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Thanks to Hylaphone, I have a HP 6920B Meter Calibrator.
Image

It doesn't quite meet its accuracy spec, but I only use it as a stable reference source, and set the value using my HP 3468A meter. That's a bit of a problem for the higher voltages, as the HP 3468A only goes to 300 Volts. I've been using my Fluke 27/FM for the higher voltages. I have a Fluke 8050A that would be better than the 27/FM, but it's a little flakey so I don't really trust it until I go through it again. (I suspect the problem is just dirty switch contacts.)

Now that I've got my HP 3456A working, I need something better to calibrate it. I do have a Julie VDR-106 six decade Kelvin-Varley Divider and a Geller 10 Volt lab reference. I need a null meter and a Hamon divider to complete the setup, assuming the HP 6920B is stable enough to transfer a voltage from the Geller to the HP 3456A. Otherwise I'll need a better meter calibrator.

I have a sad looking HP 413A null meter. The individually-calibrated meter scale is suffering from the photographic emulsion lifting from the meter card. That's a common disease among HP's fancy computer-calibrated meters. I don't know whether the specs are good enough to use for trying to calibrate the HP 3456A. I'm thinking of building a variant of Conrad Hoffman's null meter, using a nice Simpson 50-0-50 ĀµA movement I have in my stock.

I've salted away enough of those bargain-priced Vishay bulk metal foil resistors to make a Hamon divider covering 10:1 and 100:1, along with the 2:1 reference divider needed to calibrate the Hamon. So that's on the project list too.

Finally, as I wrote in my other thread, I'm putting together some poor-person's resistance standards.

Truthfully, I'm hoping someone local to me has a high accuracy meter calibrator and takes pity on me, so I don't have to do the calibration the old-fashioned way :-)

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Last edited by stevebyan on May Thu 27, 2021 2:43 am, edited 1 time in total.

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 2:37 am 
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Oh, and I have a Ballantine 421 DC/AC Precision Calibrator in the restoration queue.
Attachment:
Ballantine 421 ad.png
Ballantine 421 ad.png [ 384.25 KiB | Viewed 1314 times ]


It's a unique instrument. Who else but Ballantine would think to turn a barretter into the reference for a meter calibrator?
Seriously, that's what it uses for its voltage reference. The circuit is astonishing. They generate an AC voltage and measure that with the barretter in an ovenized bridge circuit to stabilize the RMS value of the AC voltage. The bridge is ovenized to stabilize the barretter temperature, otherwise the reference voltage would vary with the ambient temperature. They use a rectifier to generate the DC voltages from the stabilized AC, and apply a DC bias voltage to compensate for the rectifier voltage drop.

Attachment:
Ballantine-421-1965-catalog-entry.png
Ballantine-421-1965-catalog-entry.png [ 350.6 KiB | Viewed 1314 times ]


You can read about the circuit in the manual for the successor, the 421A, which is downloadable from BAMA:
http://bama.edebris.com/download/ballan ... 20Book.pdf

I'd like to add a 421A to my collection as well.

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 3:06 am 
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I don't have one voltage calibrator standard but at least half a dozen in my test equipment collection which I never use. (mainly from HP and Fluke)
The issue with old voltage calibrators is that they also need to be... calibrated ! 30-40 years old calibrators can no longer be considered as "standards" unless they were periodically checked (and re-calibrated) against a higher accuracy reference standard.
The most beautiful piece in the lot is the HP740B DC standard/differential voltmeter with his big Nixie display tubes.
I don't have the Ballantine but now I need one to add to my collection !


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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 2:16 pm 
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Tubologic wrote:
The most beautiful piece in the lot is the HP740B DC standard/differential voltmeter with his big Nixie display tubes.

Yeah, the 740B is beautiful. Nice photo, too, is it from the fellow who was doing the desktop wallpaper photos of HP equipment?

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 5:35 pm 
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I worked where we had a calibrated certified 5100B which I used to calibrate my handheld Fluke and also did a Keithley bench meter with that. However I had a lab do my HP bench meter so there is no doubt. I have not payed a lab since to calibrate the other meters but as an example the Fluke 79 really did not change from year to year when I checked it so I don't think it will go out in left field any time soon and radios don't care how precise your meter is. Up to the point they are out beyond analog meter tolerances, anyway.

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 6:33 pm 
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In my relative ignorance, I have calibrated my HP 410B to my Fluke 289, as it is the newest meter that I have. I do not have any access to any real calibration equipment, so I do what I can. I am pretty sure that my DC voltages are good, and am relatively confident that my AC voltages are at least close. I used my function generator set to 1kHz for all AC measurements. Hopefully, I will not need to be more accurate than what I have available.

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 6:45 pm 
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My 'standard' is an HP 3456A. When I got it several years ago it had a problem unrelated to calibration and I have relied on it. I measured some voltage reference ICs and all agree very closely. So I assume the HP is correct, or good enough that it doesn't matter. I acquired an HP 3455A and before it died it agreed with the 3456A. So I think I am good to go, and I am so old that the calibrations will be good enough for the rest of my life.


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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 6:49 pm 
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stevebyan wrote:
Thanks to Hylaphone, I have a HP 6920B Meter Calibrator.

It doesn't quite meet its accuracy spec, but I only use it as a stable reference source, and set the value using my HP 3468A meter. That's a bit of a problem for the higher voltages, as the HP 3468A only goes to 300 Volts. I've been using my Fluke 27/FM for the higher voltages. I have a Fluke 8050A that would be better than the 27/FM, but it's a little flakey so I don't really trust it until I go through it again. (I suspect the problem is just dirty switch contacts.)



Steve, did you ever finish the Butterworth filter for the 6920B? I've been working on a filter lately and nearly have a solution. I will post it when I've finished designing the board.


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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 8:05 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
I don't have one, but would like to get my hands on one someday. My fluke 27/FM meters all agree with one another (I've got 4, I think??), and they're all plenty of precise for anything I'll ever do. But I like to have standards, and find amusement and education in using them, and learning how much effort is involved in going up to the next level of precision. Some day, I'd like to take the capacitance, inductance and resistance standards I've collected over the years off to be verified by someone with instruments a little closer to the NIST standards, so that I'll have some sort of knowledge that they are useful references or not.

To me, the most important standard to have that is out of reach for me at the moment due to current cost of the standards is frequency, but even that is just a radio wave away from WWV if you can get the signal into your radio. I'm gathering the items together to attach an S meter to one of my radios, and make a proper antenna for getting a good signal from WWV, so that I can check the accuracy of my freqeuncy counters.

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 8:14 pm 
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buffdriver wrote:
Steve, did you ever finish the Butterworth filter for the 6920B? I've been working on a filter lately and nearly have a solution. I will post it when I've finished designing the board.

I've got about 3/4 of the parts in stock for a run of ten. The schematic is about half-done in Kicad. I haven't started PC layout.

I was stalled for a while thinking about a fail-safe circuit for the filter and output amp. I've finally decided on an approach and have most of that designed. My next step is to pick out a solid-state relay for the fail-safe circuit, to kill power to the 6920B in the event of a failure. I'm looking for something I can pick up cheap through a surplus outlet.

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Thu 27, 2021 10:36 pm 
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Location: Sunbury, Ohio 43074
so.... I just have to ask .... what's Butterworth to Chebyshev ? Ya ya, I know. old joke. :mrgreen:

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Fri 28, 2021 6:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Westminster, CO, USA
This is a special purpose one I got a few weeks back. It has been very useful for checking various RF AC meters I have. It gives a clean accurate sine wave at 1Mhz with very handy attenuator level buttons for checking up and down the meter scale.

Tony

Attachment:
IMG_20210528_113719925.jpg
IMG_20210528_113719925.jpg [ 434.09 KiB | Viewed 1161 times ]

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 Post subject: Re: Meter Calibrator, who has one?
PostPosted: May Fri 28, 2021 8:30 pm 
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Location: Kennesaw, GA 30152
Tony C,
That Boonton 26A would be a welcome addition to my arsenal! Nice!


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