Advantest R6581 8.5 digit DMM mini teardown/repair

[leighcorrigall]

I took a quick glance at the translation of Chapter 13 and found that it is different from the manual I downloaded from xDevs and KO44B. There is no Figure 1 in my version.

Correct. I added the illustration from the Advantest website so that the readers would know what the A01035 cable model number was referring to in the instructions.

[quarks]

just in case anyone is looking for an original AC Option board
I still have one
https://www.eevblog.com/forum/buysellwanted/fs-advantest-r6581-parts-(location-germany)/msg3358518/#msg3358518
just send me a PM

[leighcorrigall]

just in case anyone is looking for an original AC Option board
I still have one
https://www.eevblog.com/forum/buysellwanted/fs-advantest-r6581-parts-(location-germany)/msg3358518/#msg3358518
just send me a PM

Therefore, reverse engineering of the RMS board is on my to-do list (if, of course, one day I have it).

[serg-el]

To understand the complexity of reverse engineering - I will give photos of the RMS board.

[quarks]

the AC board needs its own shielding case and connector cable to the main board (see att. pic)

[serg-el]

Interestingly enough, I discovered that the instrument has three internal temperature probes for the DCV, OHM, and AC regions (see 13.6.1 SCPI Commands). It is a nice feature of the remote commands.

One temperature sensor.
The temperature read from the multimeter is the one that was at the time of the last given internal calibration.
Since DCV, ACV and Ohm are calibrated at different times, the temperature will be different.
In the end, you can call the calibration, say DCV, separately. And when reading the temperature of the internal calibration of the DCV, this temperature will be displayed.

[leighcorrigall]

Hello,

Is anyone who owns an Advantest/ADCMT R6581(T) interested in an original used VFD? The pins are a bit ratty and need to be realigned, but as far as I know, the display works. I replaced the display recently because it was slightly dim and it has been collecting dust on a shelf for a few months ever since.

EDIT: My VFD installation guide is available in previous posts: https://www.eevblog.com/forum/metrology/advantest-r6581-8-5-digit-dmm-mini-teardownrepair/msg3550243/#msg3550243 (display replacement is challenging to perform and you should test the display before installation)

The item is free with the exception of shipping. I accept PayPal if that works.

A picture of the display has been attached. There are also two photos that demonstrate the screen abilities compared to a Fluke 5440B in various lighting conditions.

Please PM me with a short proposal/inquiry and address. I will try and get back to you. EDIT: Item is no longer available.

Thanks.

[dietert1]

There is a minor problem with the binding post mod branadic proposed. The carrier designed for the Lowthermal 2758 binding posts requires using much longer M3 screws to mount than the original sockets. Those screws are connected to guard with their heads are close to the metal front panel connected to PE. Remaining isolation distance may be less then 1 mm. Better drill the 6 mm holes a little deeper and use shorter screws again.

Regards, Dieter

[leighcorrigall]

There is a minor problem with the binding post mod branadic proposed. The carrier designed for the Lowthermal 2758 binding posts requires using much longer M3 screws to mount than the original sockets. Those screws are connected to guard with their heads are close to the metal front panel connected to PE. Remaining isolation distance may be less then 1 mm. Better drill the 6 mm holes a little deeper and use shorter screws again.

Regards, Dieter

Thank you for pointing this out, Dieter. I measure the screw head depth to be 0.94 ± 0.05 mm (n = 12). Would this gap be a problem when working at high voltage? When I have time, I think I will put some electrical tape or a thin insulative layer between the LowThermal binding post adapter and the front panel to prevent accidental contact to ease my mind.

[dietert1]

No real problem as long as there is no short. As far as i remember 1 mm of dry is air is good for about 10 KV but electrical safety rules are more stringent. With the original sockets and their short screws the distance is about 5 mm. Apropos using the meter with higher voltages: The front end of the R6581T has a relay for that which needs exercise every now and then, just like the front/rear relay. I mean if you want to use the meter at ppm or sub-ppm levels. No different from other high resolution meters.

Regards, Dieter

[guenthert]

>  1 mm of dry is air is good for about 10 KV
I remembered 2kV, but [1] says 3kV.  I wouldn't cut it that close though and rather err on the safe side.

[1]https://hypertextbook.com/facts/2000/AliceHong.shtml

[dietert1]

Yes, about 3 KV/mm is a better number. Anyway, depending on how clean the air gap remains, electrical safety rules say 1 mm is good for 250 V (some dirt) to 400 V (clean). For 230 VAC 3 to 5 mm are recommended. These numbers no longer require rounded corners and are independent of air pressure (height).
Anyway binding posts are not completely safe, especially when used with copper lugs.
By the way the original sockets of the R6581A have a copper tube inside with a plug around it made from white metal and with the copper wiring crimped to the plugs. There is a large contact area between plug and tube, in order to reduce temperature difference and thus thermal EMF.

Regards, Dieter

[leighcorrigall]

A calibration service provider has explained to me that the DMM ohmmeter range of 10M, 100M, and 1000M is not functioning properly (out of tolerance).

I find it strange that the instrument is completely calibrated with exception of those ohm ranges mentioned.

Can anyone please explain the OCOMP ON/OFF feature of the R6581T (bottom left corner of attached image from Mickle T)? I suspect that they may have not selected the proper settings before performing an external calibration or during the verification process. Can anyone speak to this? The manual does not describe it. If this is the problem, where can I find instructions on how to configure this setting from the front panel?

 

Thank you! I am a bit under the gun because the company wants to send the instrument back soon without a complete calibration.

[leighcorrigall]

Can anyone speak to this? The manual does not describe it.

This description appears to be on section 3, page 18, number 3. I will have to translate it. 

[leighcorrigall]

Can anyone speak to this? The manual does not describe it.

I will have to translate it. 

Original text:
(3) 修オフセット電圧補正機能の設定

抵抗測定は、内部の基準測定電流を比測定抵抗に流して発生した電圧を測定しています。たとえば、リードの熱起電力などのようなオフセット電圧があると誤差になってしまいます。OHM-COMP機能によって、このようなオフセット電圧をキャンセルすることができます。OHM-COMP機能をオンにすると、通常通り測定電流を流して電圧を測定し、次に測定電流を流さないで電圧を測定します。両者の差をとることによってオフセット電圧をキャンセルでき、誤差のない抵抗測定ができます。オフセット電圧補正機能が、有効なのは10Ωレンジ〜1000kΩレンジです。10MΩ，100MΩ，1000MΩレンジでは、OHM-COMP機能がオンであっても、オフセツ卜電圧補正は行いません。

Google Translation:
(3) Offset voltage correction function setting

For resistance measurements, a voltage is generated by passing an internal current reference through the ratio resistor. For example, if there is an offset voltage such as the thermoelectromotive force of the lead, it will be an error. The OHM-COMP function can cancel such offset voltage. When the OHM-COMP function is turned on, the measured current is applied as usual to measure the voltage, and then the voltage is measured without the measured current. The offset voltage can be cancelled by taking the difference between the two, and resistance measurement without error can be performed. The offset voltage correction function is effective in the 10 Ω range to 1000 kΩ range. In the 10MΩ, 100MΩ, and 1000MΩ ranges, offset voltage correction is not performed even if the OHM-COMP function is on.


Question: How is this feature being listed in Mickel T's ACAL steps 13 and 14 if it doesn't correct for voltage?

Should I ask the laboratory to turn this feature on before running the calibration?

[leighcorrigall]

I also quickly have translated section 3, page 19, number 5. I am guessing that the resistance measurement current may also be related. I really wish that the calibration steps made note of these settings before I sent the instrument in for calibration.

Original text:

(5) 抵抗測定電流の選択

抵抗の測定電流は、HI-POWERまたはLOW-POWERに選択できます。それぞれの電流 値は、[表3-8]を参照して下さい。HI-POWERはLOW-POWERに比べて確度良く測定ができますが、比測定抵抗での消費電力が大きいため、測温抵抗体など自己発熱の影響を受けやすい素子の抵抗を測定する場合は、LOW-POWERが有効です。

Google Translation:

(5) Selecting the resistance measurement current

The measurement current of the resistor can be selected from HI-POWER or LOW-POWER. Refer to [table 3-8, page ] for each current value. HI-POWER can measure more accurately than LOW-POWER, but since it consumes a large amount of power in the ratio measurement resistor when measuring the resistance of a device that is easily affected by self-heating, such as a resistance temperature detector, LOW-POWER is enabled.

[Kleinstein]

For the highest Ohms ranges the may not be much choice in the test current. They just need the lowerst test current for the highest ohms.

The high ohms ranges may not work with a short integration time (e.g.  < 10 PLC) if the Az mode is selected. One may even get better readings in the non AZ case with high Ohms (10 M or more). The non AZ modes adds a little offset error, but less "leakage" / no charge injection form AZ switching, that can look like leakage with a high resistance source, especially if the is additional cable capacitance.

The high Ohms measurements are relatively sensitive to leakage currents, e.g. from a dirty board. The ACAL procedure does not fully compensate for this (there can be slightely different leakage paths). So it is possibility that a meter may acurally fail on the high ohms range. One may habe to live with a larger tolerance for these ranges.  I remember other reports on problems with high ohms.

A similar porblem with high ohms is also on the calibrator side - switching and the cables may add errors. So the calibrator / cal lab could in principle also be the problem. Chances are one would need manually connected precision resistors, not a calibrator like FLuke 57xx. The high ohms part may not be used very often.

[leighcorrigall]

...

A similar porblem with high ohms is also on the calibrator side - switching and the cables may add errors. So the calibrator / cal lab could in principle also be the problem. Chances are one would need manually connected precision resistors, not a calibrator like FLuke 57xx. The high ohms part may not be used very often.

Hi Kleinstein,

Thank you for the quick response and comments! I'll try and ask them about the settings they used before they go at it again tomorrow. All I know so far is the attached report. According to the document, they are using precision resistors for the high-ohm ranges.

EDIT: OOT is an abbreviation for 'Out of Tolerance' from the second last page.

Regards.

[Mickle T.]

1) External calibration (as well as internal one) doesn't use any of the user-defined settings in the DMM.
2) The main problem with R6581T is a "T" symbol R6581T - is a technological multimeter. It used only for ADVANTEST T2000 IC/SoC/ASIC test system, but not in metrology laboratories. R6581T don't have any official specs or manuals.

[leighcorrigall]

1) External calibration (as well as internal one) doesn't use any of the user-defined settings in the DMM.
2) The main problem with R6581T is a "T" symbol R6581T - is a technological multimeter. It used only for ADVANTEST T2000 IC/SoC/ASIC test system, but not in metrology laboratories. R6581T don't have any official specs or manuals.

Interesting, Mickle. Perhaps, the Advantest is working as it should.

[Kleinstein]

The high ohms may need 2 wire mode instead of 4 wire mode. At least this would reduce the chance for leakage a little. In the MOhms one does no longer care much about wire resistance.

Another setting that may effect the measurement is the capacitor at the input that can be connected. It comes with an odd name (protected or similar).
It may effect especially the 100 M and 1 G range, as the settling time could be long.

The ACAL and external CAL use fixed settings. However here it is about a performance verification. So the DMM is running a normal measurement.
For the resistance ranges the best results are likely with different settings depending on the ranges. Not sure if there is such an automatic settting is available. The 4/2 wire case also effects the cables needed.
The instructions should tell which mode to use best for the resistor range and for which settings the tolerances apply.

[dietert1]

In your preliminary report there are results "as found" and "as left". Does that mean they checked once more after adjustment? How is it possible that the 1000 MOhm was adjusted from 953 to 984 and not to 1000? Doesn't that mean the calibration setup was is unstable?
Currently we have a R6581A, and it behaves a bit strange although i applied the bug fixes mentioned above. I got the impression it remembers temperature over several days, similar to what i found in precision measurements of an Alpha Electronics foil resistor. Maybe humidity.

Regards, Dieter

[leighcorrigall]

In your preliminary report there are results "as found" and "as left". Does that mean they checked once more after adjustment? How is it possible that the 1000 MOhm was adjusted from 953 to 984 and not to 1000? Doesn't that mean the calibration setup was is unstable?

...

Hi Dieter,

'As found' is likely how it came into the shop prior to calibration.

'As left' is what they did in their third attempt at calibration. They told me they tried the procedure 3 times and were unable to achieve high-ohm measurements within tolerance.

See second last page for descriptions.

Regards.

[dietert1]

Just connected two 1 GOhm resistors. In 2W mode and with 100 PLC the variation is 853,4 to 853,8 for one resistor and 884,7 to 885,1 for the other one. Spread/walk is independent of guard connection and this was using short unshielded cables. Addition of a 2 nF high voltage cap reduced short term noise but not the spread. Anyway the instrument should calibrate to 1 MOhm or better.
Spec seems to be +/- 5 MOhm, so our R6581T wouldn't have that problem. Also i think the remark of Mickle T. may be correct, yet i haven't seen a demonstration that a R6581 is any different/better for the DC part.

Regards, Dieter

[RandallMcRee]

I have one of these meters. I have never calibrated it. I have a calibrated K2001, however.

As Mickle points out it is not a serious metrological instrument. There are some pages on EEVBLOG which show that INL is typically not stellar for the 6581T.

That said, I get a lot of good use out of it, bearing in mind its limitations. If I were you, I would not fret too much about the calibration failure in the high ohms ranges. What I typically do is acquire resistance (and voltage) standards in the ranges that are of interest and I re-measure the instrument whenever a "serious" measurement is to be taken. I have more than three good meters so this gives me some confidence that drift is low, the meter warmed up and so on.

I guess this is the "three clocks" solution.