Infiniium 54846A calibration error with modern probe - Page 1
Forum section: electronics / testgear

author: EE-digger
author_rank: Frequent Contributor
timestamp: February 28, 2019, 03:58:15 am
content: Not wanting to shell out $500 each for Tek probe adapters, I decided to sell my Tek probes, break down and start buying Agilent/Keysight.I just picked up an N2796A, very nice probe and works great on my 3000T. Unfortunately, I figured the old 54846A wouldn't have any problems since it has the full AutoProbe interface. While it gets the probe name right, that's just a simple matter of reading that string from EEPROM.Calibration fails when the probe ratio is set for 10:1, saying attenuation is an out of range value. What's disturbing is that on borrowed Tek adapters, with Tek P6245 probes, I had NO problem in calibrating.I guess I'm just looking for comments, including any possible solutions. Probe cal is close and I can always key in a real cal factor.Just bummed out that the expensive new probe doesn't work.On the Keysight forums, a solution from Al G. for a similar problem was to "buy an older probe" or "buy a newer scope". So much for a standard interface. At least with Tek, you know for sure that a newer series probe ain't gonna work on an older scope, for starters it can't even plug in.With Agilent / Keysight, who I still love dearly, you have AutoProbe, AutoProbe Lite which is not quite the same, and AutoProbe probes too new for the original AutoProbe even though there is no magic required different from prior probes (ok, I guess except for QA stuff which has been mentioned in the past).I guess this leaves me with some not so nice thoughts about the planning behind the AutoProbe interface.Going forward Keysight, your interface needs to have basic function sets/classes implemented for standard probe types (single ended, diff, current). Even if a full offset range is not available for instance, at least a future probe will still offer basic functionality.Sorry for being long winded.RANT OFF

author: EE-digger
author_rank: Frequent Contributor
timestamp: February 28, 2019, 11:28:51 pm
content: Too long winded for sure.Here's what I discovered which may be of interest to some.The 54846A probe dialog shows the probe about 80% correctly. It mistakenly shows probe attenuation as 0.1 instead of 10:1 as an 1152A does. It also shows offset as 1.2V which is not correct.There's nothing much one can do about this since it works fine on the newer scope.But again, going forward, it would nice if AutoProbe acted more like a standard. These incorrect parameters clearly aren't in the right locations for being read by the old scope.If one were intent on making it work on both scopes, and lots of spare time, they could add a small switch and new eeprom. The switch would select one of two storage blocks, one normal and one "adjusted" for the older scope.

author: Someone
author_rank: Super Contributor
timestamp: March 01, 2019, 01:37:44 am
content: There is no "standard" interface within their probes, the endpoints and configuration varies even between outwardly similar probes. So each family of probes needs a full driver on the scope to operate correctly. Not only are there forward compatibility issues as you discovered, but also artificial backwards compatibility issues:https://www.eevblog.com/forum/testgear/1159a-differential-probe-modupdate/That works ok if you only want the probe to target a specific scope platform and it treats the probe as "dumb", but if you want to support several platforms and retain the smarts it gets much more complex.