RIGOL DS1054Z - voltage calibration off - feature or looming issue? - Page 1
Forum section: electronics / testgear

author: Lorenzo_1
author_rank: Regular Contributor
timestamp: July 20, 2020, 03:56:51 am
content: Was using RIGOL to look at some circuit voltages recently and found this apparent difference between two nodes that should have been common (one on a socketed opamp and the other on a connected transistor). First thought was perhaps a problem with the socket, but substituting LeCroy for RIGOL using same probes/same connections showed no voltage difference. What surprised me was the difference in voltage between the two lines - around 0.16V. Anyway, decided to do an auto recal (for the first time in many months) through the system menu and this cured the problem immediately. Lines came into vertical alignment.My question is whether this amount of vertical separation between channels is commonplace on this model and within the typical range for autocal correction. Or does it look too high to be normal and perhaps an indicator of something going awry?

author: james_s
author_rank: Super Contributor
timestamp: July 20, 2020, 04:21:46 am
content: What happens when you place both probe tips together on the SAME node?What you're seeing could easily be drop across the resistance of a trace depending on how much current is flowing.

author: Fungus
author_rank: Super Contributor
timestamp: July 20, 2020, 05:13:23 am
content: Quote from: Lorenzo_1 on July 20, 2020, 03:56:51 amYes.Was it a very hot day when it happened?Quote from: Lorenzo_1 on July 20, 2020, 03:56:51 amDon't think so.Quote from: Lorenzo_1 on July 20, 2020, 03:56:51 amThere you go!

author: Lorenzo_1
author_rank: Regular Contributor
timestamp: July 20, 2020, 05:28:36 am
content: Thks for the quick replies. Tested same node readings for both probes - same readings. And it was pretty cool when I was doing this - perhaps 21C. I've not seen such differences on my LeCroy (though I think that one does regular autocals while in use). So was a bit surprised by this instance with the RIGOL. The voltage offset was enough to be material in trying to work out what was going on in the circuit. Good to know it's normal and not atypical.

author: james_s
author_rank: Super Contributor
timestamp: July 20, 2020, 05:46:39 am
content: That doesn't seem right, 0.16V discrepancy with both probes on exactly the same point in the circuit? When I do that with my Tek the two traces are bang-on, right on top of each other. While I don't expect Tek performance out of a low cost entry level scope, I would expect it to be significantly better than what I see there.

author: Fungus
author_rank: Super Contributor
timestamp: July 20, 2020, 05:55:21 am
content: Quote from: james_s on July 20, 2020, 05:46:39 amSo was the Rigol after pressing auto-cal.

author: james_s
author_rank: Super Contributor
timestamp: July 20, 2020, 05:56:19 am
content: Ooh, I thought he meant that discrepancy was *after* auto-cal.

author: Lorenzo_1
author_rank: Regular Contributor
timestamp: July 20, 2020, 02:15:38 pm
content: It was indeed out of whack before the recalibration as Fungus says. Came good but I wasn't sure whether this amount of 'drift' was normal. Pleased to know it's not unusual. I don't need any more gear that needs fixing just now.

author: Fungus
author_rank: Super Contributor
timestamp: July 20, 2020, 03:42:06 pm
content: Quote from: Lorenzo_1 on July 20, 2020, 02:15:38 pmIf it's months since you did it then it could be a summer/winter thing.FWIW: The manual recommends doing an autocal whenever the temperature changes by 5 degrees Celcius (or more).

author: David Hess
author_rank: Super Contributor
timestamp: July 20, 2020, 10:01:21 pm
content: That amount of drift would be unusual with an older DSO but if it is within the automatic calibration range, then I would not worry about it. Good designs can achieve a warm-up drift of 500 microvolts or less but this is less important when automatic calibration is available.Looking at Dave's reverse engineered DS1000Z schematic, the input offset could potentially drift at least 1 millivolt over 10 degrees.

author: Fungus
author_rank: Super Contributor
timestamp: July 21, 2020, 07:45:21 am
content: Quote from: David Hess on July 20, 2020, 10:01:21 pmTurn one on and watch the offset from the zero marker over the first five minutes of warmup. It's very noticeable.