Electronics > Metrology

Guildline 4410 or Advantest R6581/T For Lab Cornerstone Standard?

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denimdragon:
 Big guns, I need some guidance. I have been on the hunt for a voltage standard or 8.5 digit multimeter to serve the same purpose. The multimeter would be great because I could have more than one NIST traceable parameter, e.g. DC Volts, DC resistance, etc., but I acquired a Fluke 5450A late last year so the resistance traceability is no longer an issue once I have it calibrated.

Other than the normal "voltnuttery'' addiction we all share, I plan to manufacturer hobbyist level standards that are affordable and sell them, so I must have the best in house references that I can afford to do so. My budget is $3K.

I have been hunting for a 3458A, and I have been able to find reasonable ones, but the logistics has been a nightmare trying to get one. I missed a cal'd opt 001 002 this week because I didn't have the time to travel and get it, nor the extra $340 it was going to take to have it shipped from Californa (the meter went for 4K along with accompanying 34401A, Fluke Hydra, and some other cheap meter. That's 4k, before taxes and buyers premium). That sucked...

So now I am considering the Guildline 4410 10V and 1.018V standard or the Advantest/ADCMT 8.5 digits meters which I have found fit in my budget. I'm leary about the R6581/T, 7840 etc., because I have heard the noise floor is rather high, there isn't much info (...I have read) about repairs nor english schematics. Those are major concerns, but if need be, I should be able to work around that.

I don't know a lot about the Guildline 4400 series, but I have heard good things about it. And I have NOS LM129H vrefs that the unit comes with. I know vrefs don't really die, but the fact that I have those makes me feel a bit better, and from what I have read here, they are pretty stable (single digit yearly ppm stability?).

I have a Fluke 5440B I have had for a while that I have yet to be able to repair because of the outgaurd error, and the unreliability of the relays puts me in another possible high upkeep situation. I intended to repair it, have it cal'd, and use it as a reference since its a legendary piece when it come to stabilty. I don't have the luxury of that anymore since I want to have these products on the market before the year is out.

I am open to suggestion to my end goals stated above if someone has another direction I can take.

Thanks in advance.

alm:
What uncertainty are you aiming for? It makes a big difference if you are trying to deliver standards with a 0.1% uncertainty or a 50 ppm uncertainty. Given the equipment you're talking about I'm guessing it's more like 50 ppm or better.

I don't have experience with the Guildline / Statronics voltage standards or Advantest meters, but I can say in general that a voltage standard makes for a better voltage standard than a DMM when they are in the same class. Just look at the 1 year stability specifications which might be sub-ppm/yr for a good voltage standard and maybe 3 ppm/yr for the very best bench DMM. Calibration of a voltage standard might also be cheaper and is certainly simpler, since a DMM generally needs more stimuli. So if the goal is to deliver voltage standards you can rely on with the lowest uncertainty, then a voltage standard would be the superior solution.

The only caveat is that you need to be able to transfer the voltage from the standard to the device under test. With a DMM this is trivial: just measure the device under test. With a voltage standard if they are both 10 V, then you could connect the negative terminals together and measure the difference between the positive terminals with a 6.5 digit DMM. Because this DMM is only measuring a very small voltage, even 1% uncertainty in this small voltage will translate to a small uncertainty in the total voltage. If the values are not close, like a 10V standard and a 5V dut, then transferring is less straight forward. If you have a Kelvin-Varley divider or DMM with a high guaranteed linearity, you can use this to transfer 10V to 5V. A 3458A can do this job well due to its very high linearity. Same with the Fluke 720A or ESI RV722 Kelvin-Varley dividers, though they are certainly much more fiddly and sub-optimal for any kind of production. The 3458A and Fluke 720A have the advantage is that the linearity is inherit in the design or in the case of the Fluke 720A can be adjusted using just a stable voltage source and null meter. In this case you don't use the DMM as a voltage standard, just as a ratio device that measures the ratio between two voltage standards.

Calibration is about having a history saying that at point 1 in time the device was at value X, and at point 2 in time it was at value X+delta, so probably between points 1 and 2 the value was between X and X+delta. The more history, the more confidence you have that this is true. So if you want to use a standard (voltage standard or multimeter) down to its specifications, you ideally want to build up some history of calibrations. Also if voltage references have been turned off for a long time (months or years) and may have sat in a cold warehouse, you expect the initial drift to be higher. So ideally when buying a new standard (of any kind) that you want to keep in calibration, my suggestion would be first power it for at least two weeks and monitor its stability to the best of your abilities, and then send it out for calibration. Make sure you get data and that the uncertainty they deliver is low enough for you. Try to monitor stability within the means you have available. Then after a year or less, send it out again for calibration, and compare the data to the previous calibration. Only after this year (or three months or whatever the time is between calibrations) would I really trust it. So have a look where you could have the units calibrated and what it would cost. Don't be surprised to spend a substantial part of your budget on calibration.

So very roughly these are my suggestions from highest uncertainty and lowest cost to lowest uncertainty and highest cost:

* A good 6.5-8.5 digit bench DMM
* A voltage standard with decent 6.5 digit bench DMM (great uncertainties for voltages close to the voltage standard)
* A voltage standard, Fluke 720A/ESI RV722 Kelvin-Varley Divider and null meter (if you have more time than money, though still not cheap)
* A voltage standard plus 8.5 digit bench DMM, ideally HPAK 3458A (better uncertainty than KVD and much more convenient)

Conrad Hoffman:
I'd love a 3458 but it's just not in the budget. IMO, anything you can find at the $3k level is going to be risky. Demand is still pretty high. Voltage standards are a better bet, but a single one won't do what you need. You need a minimum of three to intercompare, so you can have one calibrated and still know where everything is. What you want to do can be done on the cheap, but "cheap" is going to cost you well more than $3k, or you have to be very lucky with eBay finds and such. ESI, Fluke and Julie all made good KVDs and IMHO you really should have one.

alm:

--- Quote from: Conrad Hoffman on February 24, 2024, 05:56:11 pm ---Voltage standards are a better bet, but a single one won't do what you need. You need a minimum of three to intercompare, so you can have one calibrated and still know where everything is.
--- End quote ---
To be clear, this applies to any kind of standards. So voltage standard, resistance standard, frequency standard, DMM, etc. Having multiple cells in one, like the Guildline 4410, sort of satisfies this. Sort of, because when sending out for calibration, you are sending them all out, so you have no way to check how much it drifted during transport. But it does depend on how close you want to get to the limits of performance. If your requirements are well below the manufacturer's specifications, then I would be less concerned about this than if you are trying to exceed those specifications (which is definitely feasible for a good standard).

Kleinstein:
For the R6581 (T) there is a thread here in the forum about repairs, that also includes a reverse engeniered schematics. AFAIK noise is not so much the problem. The more common issues are a dim display with no easy fix and quite some input switching spikes. The 6581T version often has a not so good factory calibration and this way has not so good linearity. So the lower price also comes with lower performance. It is still one of the cheaper 8 digit meters with a LTZ1000 based reference.

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