Keithley 2410-C sourcemeter bug or fault? - Page 1
Forum section: electronics / testgear

author: olewales
author_rank: Regular Contributor
timestamp: April 07, 2022, 06:45:51 pm
content: Hi,I bought a Keithley 2410-C SMU on auction and encountered a strange behavior. After powering on if I go straight to sourcing voltage then actual compliance current seems to be much lower than displayed. If I switch to current measurement instead of output voltage measurement or I edit compliance current then everything works fine. You can see this on this video I recorded:I know this is current problem because if I disconnect multimeter leads (so there is absolutely no load on the output) then I can go as high as I want with volts. (also uA symbol blinks but it is hard to see here because of VFD flicker)I have restored "bench" factory defaults before testing itCan someone confirm/deny that it is a known issue? I bought it from someone who was unable to test it thoroughly but got it from company liquidation and claimed it is working so I can probably return it if its faulty.Thanks.

author: merox
author_rank: Regular Contributor
timestamp: April 09, 2022, 08:18:07 pm
content: Quote from: olewales on April 07, 2022, 06:45:51 pmI think Keithley would call this "working as intended" even though this behaviour is kind of strange.I've never really worked with the 2410 by using it's front panel because I only control it via GPIB in out automated test racks at work. A few years ago I had the "pleasure" to implement the ability to control the 2410 in the software we use because the older 237 models were becoming kind of fault-prone.I came across a lot of strange behaviours, including the one that you are experiencing in that video. I don't remember all the details and I can't look at my source code right now but let me try to explain what Ithink/rememberis the cause of this.The root of this seems to be, that when you set a compliance level the actual circuitry that measures/controls the actual current limiting (in your case - in my case I experienced this while trying to souce current and having set a compliance voltage) starts in the lowest measurement range possible or at least in a range that is lower than you would expect for the compliance level you've set. This also means that the maximum current that can flow is the maximum current that this (lower) range can measure. There seems to be no auto-ranging at this moment. My work-around was to issue a dummy "READ?" command (take a measurement) as this seems to trigger auto-ranging in the compliance circuitry leading to the correct compliance current/coltage beeing set.Hope my writing makes sense to you - in conclusion I'd say that your device is working "as intended", as stupid it might seem

author: olewales
author_rank: Regular Contributor
timestamp: April 11, 2022, 05:33:04 pm
content: Thanks!After fiddling with it for a while I came to the conclusion that this is exactly what happens. Current measurement auto-ranges only when it's displayed (even though it's obviously measured continuously). Me pressing Measure-I button is equivalent for your dummy READ command. This would be much less confusing if compliance current (or voltage) was displayed in appropriate range (or even if it wasn't displayed all the time at all). It isn't very intuitive but at least now I know

author: gamalot
author_rank: Super Contributor
timestamp: April 11, 2022, 06:14:40 pm
content: I am very interested what model multimeter you are using?

author: olewales
author_rank: Regular Contributor
timestamp: April 12, 2022, 07:21:38 am
content: Quote from: gamalot on April 11, 2022, 06:14:40 pmIt's Voltcraft VC870

author: gamalot
author_rank: Super Contributor
timestamp: April 12, 2022, 09:24:37 am
content: Quote from: olewales on April 12, 2022, 07:21:38 amThe input impedance of your multimeter is 10M ohms. Why does the current exceed 100uA when you use it to measure 15V voltage? Did you connect any resistor to the output of the SMU as a load?

author: olewales
author_rank: Regular Contributor
timestamp: April 21, 2022, 03:07:39 pm
content: Quote from: gamalot on April 12, 2022, 09:24:37 amThat's exactly the quirk that got me: It doesn't. Despite showing 105uA compliance current the ACTUAL current is limited at the top of selected range (that's why uA symbol is flashing. If it was limiting at set value "compl" would) and it seems to default to 1uA range. When I switched it to current measurement it immediately auto-ranged and wasn't limiting current anymore

author: gamalot
author_rank: Super Contributor
timestamp: April 21, 2022, 06:05:03 pm
content: Quote from: olewales on April 21, 2022, 03:07:39 pmSorry I didn't read carefully.