Products > Test Equipment
Can I trust this cal cert
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AVGresponding:
This can be a useful resource for someone looking for cal labs in the UK:  https://www.ukas.com/find-an-organisation/browse-by-category/?cat=708
grumpydoc:

--- Quote from: Kleinstein on June 03, 2023, 11:02:49 am ---A few of the zero readings look odd and would be out of specs:

--- End quote ---
I assume these are readings are with the inputs shorted.

FWIW I get +00.00002 on the 20V range when set to 6.5d resolution - and +00.000027 in 7.5d mode.

Given that the spec seems to be ±counts in 6.5 digit mode I think that's OK and my meter is actually within specification.



But I'm not sure about the voltages that they specify - 2 counts on the 2V scale would be ±2.0µV, not 2.9µV and 20µV not 40µV for the 20V scale.

How do you get a 2001 to display 8.5 digits?

Thanks to mendip_discovery for an explanation of the differing standards levels.


--- Quote from: mendip_discovery on June 03, 2023, 09:33:49 am ---Technically unless its got an uncertainty you have no way to judge the measurements.

--- End quote ---

This bugs me - as I said, I have assumed that they used a calibration source which itself was stable enough for a meter with a 12 month accuracy in the 20-30PPM range. If the rule of thumb is to have a source with 1/10 the uncertainty then you'd need to be in the vicinity of 3.5 to 2.5PPM - hence my example of the 5730A.


--- Quote ---With regards to recalibrating stuff, unless you have good standards in the lab you risk making things worse if you adjust.

--- End quote ---
Which makes it reasonable that they would not run the meter's calibration and just run a check and only adjust if the meter was out of spec.


--- Quote ---Just looking at the cert one of the things that stand out to me is the specification for the DC stuff, PPM then goes to show µV.

--- End quote ---

I guess working out the acceptable deviation in volts is easier for people to understand. 52µV is actually correct for the maximum deviation on the 2V range for a 1.9V input - but only for the 2001 itself. I really hoped they would have included their calibrator/meter's uncertainty as well - for approx 3.5PPM you'd have to add another ±7.0µV making the actual allowable deviation more like ±59.0µV


--- Quote ---I also don't like the 10 Ω statement as its very rare to have a 10 Ω exactly out of a calibrator, I would no doubt be ok for the 3.5 digit meters but at 7.5 you will be in the area where a few µΩ/Ω of error is visible.

--- End quote ---
I don't know calibrators handle resistance - just switch in a precision component?

I guess the big boys will offer better precision but the best that Mouser or Farnell stock is in the order of 0.01%


--- Quote ---I would say use this cert as it is better than nowt. How many bits of kit are sold on the bay each week with no history and statements such as "not tested" etc. At least you are buying with some confidence even if it is just a small lab doing a cheap calibration.

--- End quote ---
When I frequented rallies (I don't have time these days but might try to get to Newbury on the 25th of June as that always used to be good) we always used to observe that there would be two bins - "Tested, working" and "Not tested".

The suspicion was always that "Not tested" meant "Not working" and I've tended to carry that logic forward to eBay.

I've no idea what the 11/09/06 date represents. It's not the date of this calibration check.


I've messaged the lab to ask what they used - if they tell me, great. If not, well, I'm no worse off than I am now and it will be a lab I know not to use :)
Kleinstein:
Having an uncertainty 10 x better than the DUT specs is an ideal situation, but rare for the higher end instruments.  They can get around with less, but than should note it, when there are some results in the grey zone (reading + calibrator uncertainty gets out of spec for the DUT).
So it is not adding the calibrator uncertainy to the meters specs, but subtracting it to get the good zone. With a not so good calibrator chances get larger to get a values in the gray zone where they can tell if the meter is still in spec or not.

Getting a zero reading of 20 µV or 27 µV in the 20 V range is still not a good result. The specs seem to be for zero stability only, not the absolute value. Stability would need a time frame for that and with the waiting time not a spec one would like to test.
The data shown in the table are 240 µV and that would be bad - makes me wonder if it could be manual reading and a typo ?

I don't know the details on the K2001, but ideally there should be a point to adjust the zero. This may be even in the more user domain, outside the normal adjustment procedure. The short (or open reading for the current) to not need a very special cal instrument. It is a very real option to adjust the zero readings, but not the gain.  If the data shown are correct that shpould have been done with the last calibration.

The resistors from the calibrator may be actually precision resistors with trim, at least for the more standard values. Some calibrators have simulated resistance. It depends on the system used if they actually get accurate 10 ohm, or have some known deviation that needs to be taken into account for high accuracy.

I would not worry so much obout getting 8.5 displayed digits. The K2001 is more like noise and already the 7th digits is more like borderline. Thus they already give the stability with only 6.5 digits.
Chances are the GPIB provided data have more digits and one rarely wants to write down that many numbers anyway by hand.
grumpydoc:

--- Quote from: Kleinstein on June 03, 2023, 02:20:11 pm ---Having an uncertainty 10 x better than the DUT specs is an ideal situation, but rare for the higher end instruments.

--- End quote ---
Granted, once you get into the territory of 8.5 digit meters with single digit PPM uncertainties it might be a little difficult.


--- Quote ---So it is not adding the calibrator uncertainy to the meters specs, but subtracting it to get the good zone

--- End quote ---
They didn't do that either - but I see your point.


--- Quote ---Getting a zero reading of 20 µV or 27 µV in the 20 V range is still not a good result.

--- End quote ---
I don't disagree, it's my first 2001 though so I don't know what to expect.

It's 1-2µV on the 200mV and 2V ranges.


--- Quote ---The specs seem to be for zero stability only, not the absolute value. Stability would need a time frame for that and with the waiting time not a spec one would like to test.

--- End quote ---
The spec mentions "variation in zero, 1 hour" so do seem to have a time-frame in mind.


--- Quote ---I would not worry so much about getting 8.5 displayed digits. The K2001 is more like noise and already the 7th digits is more like borderline. Thus they already give the stability with only 6.5 digits.

--- End quote ---
Strictly for amusement value only :) - actually I found out how to get it, GPIB, as you correctly guessed, allows 8.5 digits to be enabled directly or you can use the "secret menu" (hold Math + Freq down at power-on - see https://xdevs.com/guide/keithley_secret/) and then 8.5 digits appears in the resolution menu options.

I agree - 7.5 digits on the 2001 is something of a triumph of precision over accuracy, especially given (as you say) it is widely recognised as a noisy meter.

My Krhon Hite 522 is almost certainly a bit high though - if we assume the 2001 is as close as the calibration report suggests it's putting out 10.000470V when set to 10V - the max error is supposed to be 250µV for 10V output.
tautech:

--- Quote from: mendip_discovery on June 03, 2023, 09:33:49 am ---
I would say use this cert as it is better than nowt. How many bits of kit are sold on the bay each week with no history and statements such as "not tested" etc. At least you are buying with some confidence even if it is just a small lab doing a cheap calibration.

Sig:
Motorcyclist, Nerd, and I work in a Calibration Lab :-)
--
So everyone is clear, Calibration = Taking Measurement against a known source, Verification = Checking Calibration against Specification, Adjustment = Adjusting the unit to be within specifications.

--- End quote ---
This, all this.

Never noticed your Sig before .....too much speed reading.  ::)

One of our customers has from what I have seen, the best Cal lab in NZ of which I've had a tour of a couple times.....after visiting they need mop the floor of all the drooling everywhere tautech has been.  :-DD
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