Guildline 6500 Teraohmmeter Adjustment Problem

Started by Hawaii596, 10-05-2016 -- 16:20:53

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Hawaii596

10-05-2016 -- 16:20:53
If someone else has done the software adjustment on the Guildline 6500, here is my issue...

After doing the DC Voltage output adjustment, I keep getting EEROM CHECKSUM ERRORs.  Then when I go back in an review my entered ppm error values, the 1, 2, 5, and 10 Volt (+ and -) are there, but the 20 through 1000V (+ and -) are changed back to zero.

Note that the values set back to zero are more than 10000 numbers (wonder if that is a software issue?).
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

N79

#1
10-07-2016 -- 00:03:14
We had a similar issue with the 6520. It would randomly give an error during a measurement (I don't remember the exact wording) and lose all of its calibration constants. But it was all of them, not just the higher voltages so that's weird. It was extremely annoying to say the least and needless to say, we don't use it anymore.

Hawaii596

#2
10-07-2016 -- 09:52:03
After some troubleshooting, here is a synopsis of what we figured out.

We own (2) Guildline 6500's. We recently replaced all the capacitors, as one had died and the other had been dead for a while.  So all calibration constants were zeroed out.  When entering the DC Voltage output we got an EEROM checksum error. We tracked it down to being related to the ppm error we entered when calibrating the DC output error amount.

The manual doesn't cover this detail, but we figured out that whenever you enter a value greater than 10,000, you got an error.  Apparently, the meter doesn't allow such high ppm error constants.  It lets you enter them and doesn't show an error until you do a reset.

So the second half of what we found was that you need to measure the DC Voltage output with a DMM with 100 Megohm input impedance.  Our Fluke 8508A has >10 Gigaohm input impedance. We strapped a 100 Megohm Guildline resistor across. This dropped the ppm errors from about 11000 to about 600 or so.

So, apparently, problem resolved.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

briansalomon

#3
10-10-2016 -- 17:08:11
That's useful information. Our HP 8902A responds in a similar way if you try to input more cal constants than the software will allow but at least it gives you an error code that is a little more descriptive than "checksum error".

Bring technical excellence with you when you walk in the door every day.

Hawaii596

#4
10-27-2016 -- 12:08:42
And in the OEM manual, and in a GIDEP procedure (a NASA Cal Proc.) they are unclear.  The NASA procedure at least had the hint that they use a 100 Megohm input meter (real oddball Solartron).
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

lhiga

#5
02-23-2017 -- 07:54:57
I just completed a 6530XP calibration and was working with Guildline on this exact problem. (DCV reading OOT)  I used a Fluke 8508A  for the 1-10VDC and did a voltage bucking technique with a Fluke 5700A and a Tegam AVM2000 set at 100M ohm input Z..  Yes, the 8508A voltage reading were reading high OOT.  Originally, I was using the 8508A to try to make all the voltage measurements but found the values loading down from 30 VDC and above. So we came up with doing the bucking technique.  The problem is we also used this technique to measure down to 1 VDC and found the OOT errors followed too.  After reading the posts in this forum I will remeasure the voltages again.  But, in our local procedure I just documented everything that had transpired and DID NOT require measuring the DCV output, as long as the machine measured a resistance.  When Guildline was confronted with this there was silence.  I am still waiting and so far got no response to this issue.

lhiga

#6
02-23-2017 -- 22:07:15
ok Guildline did respond today saying they suspect something in power supply went.  My assessment, I don't think anything is wrong with this unit.   I say this because originally when I called Guildline their response was if only the M ohm ranges require adjustment they recommended just adjusting the range coefficients for those ranges.  They also added that the M ohm ranges requiring adjustment is typical of these units.
This is what I did.  I adjusted the range coefficients such that the test resistors read within a couple of ppm of the nominal.  Then I rechecked all the different ranges again.  Just to be sure.   Guildline made me a proposition, they would take the unit in and for just the cost of a certified calibration they would do the necessary repairs needed.  In other words, Guildline would eat the cost of repairs.   I also rechecked the power supply after reading the posts in this forum and this is what I found.  I rechecked the 1, 3, & 10 VDC voltages with a 100M ohm resistor across the input of the 8508A and this is what I got,
nom.      meas.        nom.     meas.
1           0.74            -1       -0.725
3           2.208          -3       -2.192
10         7.344          -10     -7.330
As you can see these voltages are way off the mark.  But, the 10 M ohm & 100M ohm resistors measured within 85ppm from the nominal.

lhiga

#7
02-23-2017 -- 23:02:52
I think I am not painting the correct picture.  Originally, I made the measurement with a 8508A and a 3458A and found the 1 , 3, & 10 V measurements reading OOT high by as much as 10,000ppm.   This is the data that I gave Guildline.  Then I read the articles in this forum and made the 8508A measurements with a 100 M ohm resistor across the DMM input.  Reading were drastically OOT Low.  Guildline got back to me saying they suspected something in the power  supply went.  I suspect there is nothing wrong with this unit.  Also, you cannot believe what is written in the manufacturers manual for measuring these voltages.  These voltages appear to be very load sensitive.  I have reverified the calibration on our teraohmmeter and all the ranges currently are within tolerance.

Hawaii596

#8
02-24-2017 -- 08:48:57
I ended up doing a lot of the same. I have two 6500's and a 6520 (I think - has a BNC and TRIAX connector on front).  I haven't yet cal'd the 6520. But I have a set of 65206 resistors to check each range on the 6500's (all of them certified by a standards lab). What I finally have given up and done with mine is I do my best to simulate the 100 Megohm input impedance, etc., and follow the full OEM procedure.  Then, I use my set of 65206 resistors to cross check each range. Each time I use the 6500 to calibrate things like a Penn Airborne resistor, etc., I pre-measure a 65206, and derive a correction factor for the range. Then I run a sample size of 25 in a spreadsheet I developed. I use the mean value as my calibrated value for each resistor I calibrate.

They are old, not that great, but they work, and they do the job.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

lhiga

#9
02-25-2017 -- 07:58:30
I have been going back and forth with Guildline particularly on the meters DCV output.  Guildline has convinced me that I should send the unit back to them for evaluation.  The metrologist I was talking to was pretty adamant about something being broken in the power supply.  Raven596 you say you follow the full OEM Procedure so how are you doing the VDC measurements? With a DMM?  Which one, because there isn't one that will give you good readings.  The Agilent 3458A, Fluke 8508A, Wavetek 1271/1281 all have the same Input Z specifications.  The DCV readings will be high from 1-10VDC and low >10VDC.

lhiga

#10
02-25-2017 -- 18:31:03
Excuse me, in my last post, I meant to say hawaii596 and not raven596 don't know what I was thinking.

lhiga

#11
02-26-2017 -- 03:11:50
So, hawaii596 from all your inputs you are saying you have made the power supply measurements with the 8508A with a 100M ohm resistor strapped across it input for the 1, 3, & 10VDC ?

lhiga

#12
02-26-2017 -- 03:14:12
Also, you have made the DMM measurements from 30-1000VDC with the 8508A?

Hawaii596

#13
02-28-2017 -- 11:24:48
Yes, there is a specific Solartron multimeter that they use in the procedure in the manual. We don't have one, and there aren't units available. So I tried to simulate the required input impedance as well as I could. Then, in the end, I have a set of 65206 resistors (and 9336 and 9337 series resistors) that I send to a standards lab. I use them to create correction factors for each range on the 6500.  Even when I follow the adjustment procedure for the 6500 exactly, there are still range errors, especially at the higher resistance ranges, and higher output voltages.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."
Lord Kelvin (1824-1907)
from lecture to the Institute of Civil Engineers, 3 May 1883

briansalomon

#14
02-28-2017 -- 16:10:49
I use HV (30KV) leads for this and other precision measurements where 1000 VDC is applied so I'm not wondering if I have errors due to leakage on the high side of the measurement.

It isn't required by my procedure but it appears to improve this type of measurement.
Bring technical excellence with you when you walk in the door every day.
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