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Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
Can I ask what's probably a stupid question about the 7150+? Assuming that the average of my collection of 14 Weston cells is correct how do I calibrate my meter. In particular the manual says something about a plug that goes in the back. What are the connections in thes magic plug?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Good question! I'd like to know too. Mine was brand new in the box with all the accessories, but the magic plug wasn't supplied, and I don't remember the manual saying how to make one.
Plus, I think I've lost the manual anyway.
According to this thread, you need GPIB to do the calibration.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
No, that's still as true as it always was. See Appendix A of Linear Technology app note AN86 ,C1,C1155,D4177 to get an idea of the techniques needed to work at the 1ppm level. It's written by Jim Williams, so it's worth reading anyway.
No matter how stable a voltage reference you build, you'll still need to get it calibrated initially. The LTZ1000 might be very stable, but it can come out of the box anywhere between 7.0 and 7.5V. And it's specced to drift something like 4ppm/year.
Bored Chemist: Thanks for the manual! I stand corrected, GPIB is not needed for calibration. And it seems to say that the calibration plug is just a jack plug with the two contacts shorted together.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
IntraWinding wrote ... Yes, those meter keep turning up. They're very old and in my experience burn out within a few hours of being powered up, but having repaired one, and having two others to fix, I'd like to get them calibrated. ...
Wouldn't it be nice if I had my own voltage reference that, hopefully, some kind person could calibrate for me and which was so well made it kept its calibration sufficiently for several years use with my meter.
From what I've read I think this would be pushing the limits of non Josephson based voltage references, but I have the advantage that I can afford to construct a system that wouldn't be considered economically viable industrially since I get my own labour for free!
... I see that 6.5 digit equates to about 0.5ppm, so I would ideally like to hold a voltage to significantly better than that for several years.
Looking forward to hearing about your results. I'm in the same boat with my 6.5 digit multimeter, an Agilent 34401A from my defunct "dot com bubble startup" employer. For now, I could take it to work and check against instruments with current, traceable calibration. But have never done that & don't know where to find the adjustment knobs (adjustment menu, these days?)
Re. portable standards: I think fractional ppm stability over years is not going to happen without Josephson junctions, or arrays of Weston cells in temperature-controlled rooms. See for example the Fluke 734A voltage standard: Its 4 independent units are each spec'd at +-2ppm/year, and the sophisticated user can do better by going statistical on them. Can you homebrew something better with inexpensive parts? [edit]The 734A is shipped under power (from temporary external battery) and must be powered continuously. Flashes a "caibration required" indicator if it ever loses mains power long enough to run down the internal backup batteries. [/edit]
Here is a DIY project along the lines of OP: Author refers to a previous project with temperature-regulated reference.
As for absolute accuracy: I remember when the US legal volt increased by 9 ppm in 1990. In the year before the switchover, cal labs had to ask their customers if they wanted old volts or new volts! (When NBS/NIST switched from Westons to Josephsons in 1972, they adopted a value for 2e/h that maintained continuity with the legacy system. Later SI determinations led to international adoption of a slightly different value in 1990. See
p.s. Just discovered a move afoot to redefine some basic SI units in 2011, by adopting exact values for a different set of fundamental constants. Would not affect the relationship between meter and second, already based on an exact value for c. But u0 (permeability of free space) would no longer be exactly 4e-7*pi H/m (or N/A^2). It could change as better measurements are made; expected change is zero and uncertainty is 0.69 ppb.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Klugesmith wrote ...
IntraWinding wrote ... Yes, those meter keep turning up. They're very old and in my experience burn out within a few hours of being powered up, but having repaired one, and having two others to fix, I'd like to get them calibrated. ...
Wouldn't it be nice if I had my own voltage reference that, hopefully, some kind person could calibrate for me and which was so well made it kept its calibration sufficiently for several years use with my meter.
From what I've read I think this would be pushing the limits of non Josephson based voltage references, but I have the advantage that I can afford to construct a system that wouldn't be considered economically viable industrially since I get my own labour for free!
... I see that 6.5 digit equates to about 0.5ppm, so I would ideally like to hold a voltage to significantly better than that for several years.
Looking forward to hearing about your results. I'm in the same boat with my 6.5 digit multimeter, an Agilent 34401A from my defunct "dot com bubble startup" employer. For now, I could take it to work and check against instruments with current, traceable calibration. But have never done that & don't know where to find the adjustment knobs (adjustment menu, these days?)
Re. portable standards: I think fractional ppm stability over years is not going to happen without Josephson junctions, or arrays of Weston cells in temperature-controlled rooms. See for example the Fluke 734A voltage standard: Its 4 independent units are each spec'd at +-2ppm/year, and the sophisticated user can do better by going statistical on them. Can you homebrew something better with inexpensive parts?
Here is a DIY project along the lines of OP: Author refers to a previous project with temperature-regulated reference.
As for absolute accuracy: I remember when the US legal volt increased by 9 ppm in 1990. In the year before the switchover, cal labs had to ask their customers if they wanted old volts or new volts! (When NBS/NIST switched from Westons to Josephsons in 1972, they adopted a value for 2e/h that maintained continuity with the legacy system. Later SI determinations led to international adoption of a slightly different value in 1990. See
p.s. Just discovered a move afoot to redefine some basic SI units in 2011, by adopting exact values for a different set of fundamental constants. Would not affect the relationship between meter and second, already based on an exact value for c. But u0 (permeability of free space) would no longer be exactly 4e-7*pi H/m (or N/A^2). It could change as better measurements are made; expected change is zero and uncertainty is 0.69 ppb.
As it's you Rich, I have a very small number of half-watt decadewise resistors 0.01% viz: 10R, 100R, IK, 10K, 100K, 1M and 10M to loan out to responsible adults in good standing with 4HV.org, to be sent back when you have finished with them.
At 0.05% I can offer on loan calibration resistors up to 1G, and at 5% up to 100G encapsulated in glass - a service available at my discretion to regular 4HV members in good standing for not less than six months. There's no charge for the loan, only for the post and packing.
Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
Hi Folks,
Yes, I've let my perfectionism get the better of me. It's damned annoying though that people make 8.5 digit multimeters when they can't make a 6.5 digit one work properly. The comparison to a car's optimistic speedometer is humorous but not quite the whole story. Over increasingly short periods these meters are stable enough to make comparisons at nearer their full resolution, so in a 5 minute period they are very accurate for measuring the ratio between two values for example.
I know the proper engineering approach to design starts by defining the goal in measurable units, but what I'm doing is ultimately driven by a wish to achieve the best I can. For example, if I built a Tesla coil I'd want to make the biggest 'best' spark I could reasonably manage, which is a vague but reasonable goal, surely? I suppose you could say I should set a specific goal. I could say, "I want 3 foot sparks," and then go on to see if I could reasonably achieve them, adjusting my goal as I become more familiar with the difficulties of this project in comparison with my resources. Actually, I guess that's what I just did. My goal of significantly better than 0.5ppm for several years is unrealistic so I'll have to lower my sights. Actually, what I'd really like is to find somewhere/one who can fully calibrate my meter so I have the DC, AC and resistance ranges all spot on, but cost is sadly very much an issue.
Solartron 7150 plus: Yes, all you need to calibrate it are suitable references (page 5.3 - not less than 50% of nominal full scale) and a shorted mini jack plug in the back. A good shorting plug for the front (or back) is also a good idea for setting the Zero points. Fluke have some handy hints on what constitutes a good one for such sensitive meters. Low thermal mass is the main thing.
Even if you don't calibrate your meter it's worth refreshing the memory as it won't retain the calibration values indefinately (page 5.6).
And it'll be a lot less confusing if you also fit the Calibration Overlay onto the keypad - page 5.4 in my manual.
Here I can help. I spent a silly amount of time making a perfect overlay in Photoshop which I'd be proud to pass on to anyone here who'd like it (as I remember making the sign wave character was a project in itself!). If printed with an inkjet on plain paper it's not too hard to cut out the holes for the keys. Use the best printing quality setting for results consistent with proud ownership . I tried printing on photo quality paper with a view to sealing it with spray on lacquer, but trying to neatly cut the holes in the thick paper drove me up the wall! I've never seen an original overlay beyond the poor quality black and white image in my downloaded pdf manual (page 5.4), but I think it looks pretty darn great
Image Size: 8cm x 13.56cm 3780 x 6406 pixels 1200 pixels/inch
This gives you two goes at cutting the holes neatly! File size 1MB:
Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
I've found a place where 'volt nuts' hang out :
But I'm still feeling sad about the facts of metrological life
Alan
PS Anyone find that calibration overlay useful?
PPS I have calibration standard 1K, 10K and 100K resistors, but of course I don't know how accurate they are without paying some lab a bundle to measure them. Hey ho! I also have a calibrated Geller SVR 10V reference which can give short term 5 or 10ppm accuracy, assumingh the plane trip over here doesn't affects it adversely
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Precision Voltage Reference
. I tried printing on photo quality paper with a view to sealing it with spray on lacquer, but trying to neatly cut the holes in the thick paper drove me up the wall! 
