RTB2004: Can't zoom in on signal - Page 1
Forum section: electronics / testgear

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 04, 2020, 09:05:16 pm
content: Hello everyone,I have a strange problem with my Rohde&Schwarz oscilloscope. I'm trying to measure a 13,8V DC signal. As soon as i try to lower my volts/div the signal goes out of the screen and i can't change my offset. The offset is stuck at 1.2volt. I already tried different channels and different probe settings, still the same issue. I have no idea what i'm doing wrong? Does anyone have any explanation for this issue? Is it impossible to look at a 13,8 DC signal with a 10mV/div?Thank you all!

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2020, 09:09:00 pm
content: Nothing strange here, this is what AC input coupling is expressly for.......to remove the DC component of a signal.

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 04, 2020, 09:12:38 pm
content: Quote from: tautech on October 04, 2020, 09:09:00 pmSeriously? I know AC coupling is there to remove the DC component. So it's impossible to look at a 13V DC signal with a low volts/div? How is the maximum calculated? Say for instance the 13VDC level has a signal on top of it, say a small block wave of around 20mV. It's impossible to see right?

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2020, 09:27:15 pm
content: Quote from: reyntjensm on October 04, 2020, 09:12:38 pmMax channel voltage offset will be specified in the datasheet and it commonly is different depending on the V/div range selected. RTFM.Some scopes permit setting a fixed vertical position so to easily allow high magnification of a signal without it disappearing off the display, again RTFM.

author: nctnico
author_rank: Super Contributor
timestamp: October 04, 2020, 09:40:57 pm
content: Quote from: reyntjensm on October 04, 2020, 09:12:38 pmUsing AC mode is one way. Another option is to use zoom mode and keeping DC coupling. You'll get the best result by using the lowest V/div which allows to see the signal (with offset ofcourse). The limit will be the ADC resolution but with 10 bit you'll have an advantage. If the signal is not high frequency then turning on high-res is another step towards a clean signal but be aware that high-res mode also filters the signal.

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 04, 2020, 09:46:34 pm
content: Quote from: nctnico on October 04, 2020, 09:40:57 pmThe manual says that with <200mV/DIV the max offset is 1.2V( i never had this situation before). So if i want to keep the DC coupling i guess i should have to tweak the probe settings to get the signal under the 1.2V, or at least the offset. What do you mean with the zoom mode?

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2020, 10:05:56 pm
content: Quote from: reyntjensm on October 04, 2020, 09:46:34 pmYes normally we might use 1x probes to look at low levels of ripple however if your R&S has sufficient input sensitivity 10x probes can be used which can often put you in another range of permissible channel offset.QuoteVertical zoom if this model provides for it.

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 04, 2020, 10:13:29 pm
content: Quote from: tautech on October 04, 2020, 10:05:56 pmI don't think my model has any vertical zoom. i will check the manualIf i use a 1: probe with a 13vdc signal i can't get below 200mV/div. So i was thinking to set the probe to 10:1 and keep the settings in the scope to 1:1. Is there another solution?

author: tautech
author_rank: Super Contributor
timestamp: October 04, 2020, 10:16:09 pm
content: Quote from: reyntjensm on October 04, 2020, 10:13:29 pmAC coupling.

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 04, 2020, 10:37:26 pm
content: Quote from: tautech on October 04, 2020, 10:16:09 pmYep, looks like AC coupling is the way to go. stupid me.... i thought such a slow square wave signal wouldn't couple trough...

author: nctnico
author_rank: Super Contributor
timestamp: October 04, 2020, 10:41:16 pm
content: Quote from: reyntjensm on October 04, 2020, 10:13:29 pmThe RTM3004 has vertical zoom for sure. Just try to make the signal bigger in the zoom area. I can't imagine the RTB2004 doesn't have vertical zoom.

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 04, 2020, 10:49:10 pm
content: Quote from: nctnico on October 04, 2020, 10:41:16 pmIt does!! i was looking over the button every time. I think i should better go to sleep instead of being stupid... Thank you for the support!