SDM3055, measurement noise - Page 1
Forum section: electronics / testgear

author: Erikk
author_rank: Newbie
timestamp: April 07, 2016, 07:26:17 pm
content: Hi.Recieved my Siglent SDM3055 today, I instantly updated to the latest firmware ( 1.01.01.16R2 ).It seems to pick up lots of noise in the leads, to the level that i´m unable to use the Fast mode in 2-wire ohm mode.It switches the input relays like crazy, I guess the relays will get worn out pretty soonhttps://youtu.be/bZduHNMjfEoThis is measuring a 40K 5% resistor.The Fluke 117 is rock solid at 39.13KWorks OK in Slow mode, but terrible in fast mode.https://youtu.be/ekpJUghxUG8The noise in Fast-Mode seems to be ~700ohms Peak-to-peakAttaching the scope probes reduces the noise to ~400ohms Peak-to-Peak and the following on the scopeIs this due to common-mode noise or is it related to grounding?My apartment does not have grounded electrical system, although all my gear is connected to one of these extension leads with grouding sockets.Would like to recieve som inputs on where to go from here..Thanks

author: tautech
author_rank: Super Contributor
timestamp: April 08, 2016, 09:01:47 am
content: Quote from: Erikk on April 07, 2016, 07:26:17 pmWelcome to the forum.QuoteI've linked this thread to Tech support, let's wait and hear what they can offer.EditThis:It is normal that the reading bounces a little value (about 700ohm when measure 40K)in Fast speed mode, we check some other vendor's benchmark DMM, it will also bounce like ours.But it is abnormal if the input relays switches crazy(Erik said in EEVblog).The reason is noise, especially power line noise. In the Fast mode, the data out rate of ADC is high, and the digital filter in ADC has no suppression with this noise.On the other side ,in the Slow and Medium mode, the digital filter provide this suppression,so the reading is stable.Most hand DMM 's reading speed is slow and fixed,so people can't notice this phenomena.And:we know the fact that high impedance circuit will easily pick up the noise,I think this is also the reason why this happened.Hope this helps.

author: pxl
author_rank: Regular Contributor
timestamp: April 08, 2016, 10:08:04 am
content: Is it makes sense at all to have fast mode for measuring resistance?

author: Erikk
author_rank: Newbie
timestamp: April 08, 2016, 10:56:04 am
content: Quote from: tautech on April 08, 2016, 09:01:47 amThanks!Quote from: tautech on April 08, 2016, 09:01:47 amYes, this seems reasonable! Thanks for your help.I will do some more tests, it´s probably some cheap-ass switching unit somewhere in the appartment who´s screaming out noise.E.g. killing the TV made quite an impact actually.Maybe try a ferrite bead on the powerline cable to see if it reduces the noise.Quote from: pxl on April 08, 2016, 10:08:04 amNo, probably not. Although it was the easiest reproducible way of capturing the noise.

author: pxl
author_rank: Regular Contributor
timestamp: April 08, 2016, 11:08:26 am
content: I mean is it any good to implement this feature in a dmm? The resistance you measure in 2w mode typically does not change that fast. Is there any sensible use case for that?I would probably not let the users to switch to fast mode for measuring ohm, or fast mode will be reasonably fast, while slow mode would be for very precise measurements.Or, it probably makes sense to start the measurement fast then refine it later with more iterations. I have no experience with pro dmms, just asking.

author: rf-loop
author_rank: Super Contributor
timestamp: April 08, 2016, 04:41:43 pm
content: Quote from: pxl on April 08, 2016, 11:08:26 amDo you think only fixed value resistors need measure?But of course, also we have different methods for measure very fast changing resistances because tusual DMM, even fast one, is hopeless slow for these.Small random exampleFSR400. Risetime <3us.But, there is many kind of things where is slowly or fast changing resistance.