Question about how to calibrate oscilloscope stuff - Page 1
Forum section: electronics / beginners

author: dc443
author_rank: Newbie
timestamp: May 26, 2022, 07:28:51 am
content: In measuring the built-in 1khz calibration signal generator on my scope (SDS 1202X-E) with both a Micsig DP10013 differential probe and a built-in probe,- The differential probe output is a bit noisier, but that makes sense since i'm comparing a 50X probe to a 1x probe. Okay.- Since the output is noisier, this is a little harder to perfectly quantify, but with the aid of cursors I measured that the height of the square wave reported by the differential probe is 3.08V whereas it is 3.01V (nearly indistinguishable from 3.0) with the regular probe.- First off, why is there a source menu in Cursors? What significance does this have other than the colorization? (OK i think i know why -- it applies the vertical window setting of the channel to provide the values in the reading.)- How can I calibrate out the 3.08V to 3.01V discrepancy? The diff probe states on it that there are no user serviceable parts inside. Could there still be resistors inside I could fine-tune if I was hell-bent on recalibrating it? Is there no feature on the scope to adjust this?- Similarly, suppose I hypothetically use some other fancy equipment to unequivocally determine that the signal it puts out is actually 2.98V. Since it's reading 3.01V and off by one part in a hundred, I might want to recalibrate this thing to actually read 2.98V and be more accurate... is this at all possible to actually do?OK i did some more research. seems like utility menu has calibration. Could this be used with the diff probe??

author: sahko123
author_rank: Frequent Contributor
timestamp: May 26, 2022, 08:14:03 am
content: You dont really calibrate the probes. You calibrate the scope for all inputs. The vertical channel of a scope is very often very inaccurate and isn't really required to be in most cases. So discrepancies like that are either because of poor factory calibration or cheap probes

author: tggzzz
author_rank: Super Contributor
timestamp: May 26, 2022, 09:12:46 am
content: The "cal out" on a scope is misnamed, but traditional.It is used to adjust the low frequency time-domain response of a probe. FFI, see the scope's manual or the basic references inhttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/Apart from that, by noting that 3.01 <=> 3.08, youhavecalibrated your system. You haven'tadjustedit, though.

author: rstofer
author_rank: Super Contributor
timestamp: May 26, 2022, 02:43:07 pm
content: Quote from: sahko123 on May 26, 2022, 08:14:03 amThere is a scope calibration procedure in the User Manual (or there should be!) and you will note that calibration is done with the probes removed. Inaccuracies caused by the probe leads are not included in the calibration. Adjusting the 10x scope impedance match is done with the front panel signal but that's only fixing the rise time problem of impedance mismatching. It has nothing to do with the accuracy of the vertical value.Don't expect to get a lot of digits in a scope display. In the first place, many scopes only use an 8 bit ADC. So spread 256 divisions across the entire screen and work out, for a given V/div, how much a single ADC bit is worth. You will never get better than that number even if everything is perfect. And it won't be...