I just got off the phone with the calibration technician. He said that he tried everything to make the R6581T measure within tolerance:
- 2-wire mode instead of 4-wire for the 10 MΩ, 100 MΩ, and 1 GΩ range (they will update the accreditation data to reflect this)
- checked both HI and LO power settings (not much difference)
- used 100 PLC for the whole procedure
- OMH-COMP OFF
Apparently, the technician had no problem with the R6581T because it is similar to the Fluke 3458 and 8508.
He mentioned that while testing, he noticed something very strange about the -1 V reading on the 10 V range. He had to calibrate the DMM three to four times to get the instrument to read correctly. This might be key to diagnosing the problem... EDIT: This sounds like ACAL R230, which is located right next to R234.
I think I must have done something wrong on my end. Maybe I overheated a component while de/soldering or left part of the board contaminated enough to have poor readings at the high-resistance range.
EDIT: Change history:
1) Branadic binding post adapter with leads soldered to posts
2) R200 - easy replacement with solder sucker because the feet were straight
3) R234 - particularly difficult to remove with a soldering iron, solder sucker, and eventually wire cutters
4) K006 - followed the picture and heat shank a cover over the green wire
5) C215 - easy to overheat, but should not be a critical component
I am going to get an estimate for the cost of repair if possible. Might as well have the instrument come out completely calibrated.
Getting trouble with -1 V in the 10 V range is a really bad sign, as this point is also used in the ACAL procedure.
Is the fix for the relay power saving bug applied ?
I received my Advantest R6581T back from Transcat today. Sure enough, it has the problem with the high ohms range. They are not willing to diagnose or repair it.
When I measure an Ohmite RX-1M 1 GΩ 1 % resistor, the reading is within tolerance initially.
After observing the meter readings for about 2 hours, I believe the measurements decay over time until a steady-state value is reached.
My guess is that the instrument reads correctly for a while but slowly drifts off course. The same values appear for both the front and rear terminals. I am going to take some time to measure all my resistance/voltage standards before opening it up for diagnostics.
Does anyone know how to explain this mechanism?
Has anyone successfully measured high-resistances with their Advantest R6581?
I received my Advantest R6581T back from Transcat today. Sure enough, it has the problem with the high ohms range. They are not willing to diagnose or repair it.
When I measure an Ohmite RX-1M 1 GΩ 1 % resistor, the reading is within tolerance initially.
After observing the meter readings for about 2 hours, I believe the measurements decay over time until a steady-state value is reached.
My guess is that the instrument reads correctly for a while but slowly drifts off course. The same values appear for both the front and rear terminals. I am going to take some time to measure all my resistance/voltage standards before opening it up for diagnostics.
Does anyone know how to explain this mechanism?
Can you measure the input bias current, preferably directly with a picoammeter, on the DCV range that would correspond to the voltage used in the 1G resistance mode? If no picoammeter is available, just shunt the input with a stable 1M resistor and a small (1-10nF) mylar or PP capacitor--each microvolt displayed corresponds to 1 pA bias current. Start with the meter cold and see what the bias current does over a 4 hour period.
The input bias might well be very time dependent, e.g. for a HP3456A I've seen spikes in the nA range for an input bias current averaging less than 100pA. A digital picoammeter might not the best tool to catch that.
Can you measure the input bias current, preferably directly with a picoammeter, on the DCV range that would correspond to the voltage used in the 1G resistance mode?
Has anyone successfully measured high-resistances with their Advantest R6581?
My R6581T is out of spec on 10M and above.