Calibration procedure / service manual for R&S NGMO2

[marber]

Hi,

I bought a second hand Rohde & Schwarz NGMO2 power supply. It's a nice two-quadrant (lab) power supply, 0..15V up to 5A, dual channel. Low noise/ripple, accurate and fast. It can act as a current sink, record measurements, is programmable, can trigger on inputs, etc etc. The fact that there are no binding posts in the front is slightly inconvenient, but I'll sort that out. At least the fans aren't very loud.

thmjpr did a teardown and description in this thread: https://www.eevblog.com/forum/testgear/ngmo1-0-15v-0-2-5a-power-supply-teardown-%28rohde-schwarz%29/msg237280/#msg237280. My unit appears to be exactly the same, except it's the two-channel version.

I've been testing it today, and it seems to work pretty nicely, and the voltage & current settings & measurements seem pretty accurate (as far as I can trust/compare with my humble EX330 & DS1074-S anyway. However, because it has a whole bunch of analysis/measurement options, it also has an extra DVM option where each output channel has an additional digital volt meter input, i.e. separate from the sense input. THAT function appears to be way off in my unit.

When I measured over the full range on both channels, both seem to consistently read at 183% of the accurate value. Seeing as both channels have completely independent hardware, I imagine this is just some wrong calibration setting/value in the unit (last cal: March '07), and not a hardware issue. This suddenly also explains the "CALIBRATED: RESTRICTED USE" sticker on the unit.

Apparently I can recalibrate the unit using either the front panel unit or remotely (RS232/GPIB), but the procedure is only described in the service manual which I don't have. I'm afraid that if I start the procedure now and can't properly do what it asks, it might screw up the current settings that are correct. And then it probably wouldn't just be this "bonus" DVM function that's way out.

Does anyone have information about the calibration procedure for this unit perhaps?

Thanks!

[marber]

(No replies and I don't think these PSUs are very common/popular, but perhaps this info useful to someone some day.

Later I noticed that the current measurement of channel B on my unit was rather off as well. Using my shiny new BM869s I ran through the calibration procedure for channel B only.

It asks to verify two voltage readings (~50 mV and ~15 V) using an external volt meter, and the exact values of 3 reference resistors (1 Ohm, 33 Ohm and 3.3 KOhm) only. The calibration can be aborted as well. The steps are exactly like the SCPI commands as listed in the operations manual.

This solved my current measurement accuracy, but the calibration didn't cover the channel's DVM inputs at all, those are still 183% over the actual value as before. I guess that's not user adjustable.

[acbern]

Have you asked R&S for a user service manual? If available, they send that for free or at a low cost. I have found them very helpfull most of the time. Only problem I had was asking for a UPL audio analyzer CAL procedure, they said its not available, which I cannot believe.

[Wuerstchenhund]

Have you asked R&S for a user service manual? If available, they send that for free or at a low cost. I have found them very helpfull most of the time. Only problem I had was asking for a UPL audio analyzer CAL procedure, they said its not available, which I cannot believe.

+1    Ask R&S support, they'll probably send you the Service Manual for free.

[marber]

Have you asked R&S for a user service manual? If available, they send that for free or at a low cost. I have found them very helpfull most of the time. Only problem I had was asking for a UPL audio analyzer CAL procedure, they said its not available, which I cannot believe.

I haven't! I guess I've been too pessimistic about my chances then. Will do so this week, thanks.

[acbern]

Just wanted to follow up if you got the cal procedure from R&S.

[cosrologist]

I acquired a NGMO2 and I also asked Rhode and Schwarz Australia for the service/operators manual.  They promptly emailed both to me for free.   The PDF's are too big to post here (3.3MB and 1.3MB).

[acbern]

Would be great if you could download it to ko4bb!

[tautech]

Would be great if you could download it to ko4bb!

+1
Here's the link:
http://www.ko4bb.com/getsimple/index.php?id=manuals

[cosrologist]

Have uploaded the manuals to K04BB - should appear soon I hope.   

[marber]

Have uploaded the manuals to K04BB - should appear soon I hope.   

Awesome!
When I asked them, they didn't want to release the service manual, only get the unit in for repair.