Oscilloscope 2nd channel is not same as 1st ? - Page 1
Forum section: electronics / beginners

author: tonycstech
author_rank: Regular Contributor
timestamp: June 25, 2023, 11:36:35 pm
content: Hi guys, i have this siglent scope sds 1202x-eWhen i use 1st probe, i get normal expected curve but when i use second channel, measuring same signal shows complete nonsense.Noise and not synchronized at all. Cannot see curve.I tried to do firmware reset and defaults but no luck.I dont seem to understand what is the cache.How to reset both channels to default otherwise ?

author: ataradov
author_rank: Super Contributor
timestamp: June 25, 2023, 11:42:22 pm
content: Are you connecting both channels at the same time? Or alternating?If alternating, then are you switching the trigger to the other channel as well?

author: tonycstech
author_rank: Regular Contributor
timestamp: June 26, 2023, 12:04:05 am
content: I am connecting both channels at same time to same or different source of signal.

author: ledtester
author_rank: Super Contributor
timestamp: June 26, 2023, 12:05:17 am
content: Are you using the "Auto Setup" button to configure the channels? If not it's worth trying.Another test would be to see if can get square waves from both channel 1 and 2 using the Compensation Signal Output terminal using the 'Auto Setup' button?See the procedure described in the "Function Inspection" section on page 8 of this Quick Start Guide:https://res.cloudinary.com/iwh/image/upload/q_auto,g_center/assets/1/26/SDS1000X-ESDS1000X-U_QuickStart.pdf

author: ataradov
author_rank: Super Contributor
timestamp: June 26, 2023, 12:15:51 am
content: Show screenshots of what you see, especially in the configuration where both channels are connected to the same signal.

author: tonycstech
author_rank: Regular Contributor
timestamp: June 26, 2023, 12:41:21 am
content: Yellow is channel 1Connected one probe at the time to the scope its self for calibration.Results are the same but 2nd channel is not synchronizing.Not sure how to adjust each channel independently when there is only ONE knob to adjust anything.

author: ataradov
author_rank: Super Contributor
timestamp: June 26, 2023, 12:42:09 am
content: Ok, but the channel 2 is not connected/enabled. You need to switch trigger to the channel 2.You see that the trigger is set to a raising edge on the channel 1. If channel 1 is disabled, it can't trigger.Not sure what do you mean by one knob. There is one common time base and independent vertical adjustment for both channels. This is pretty standard and even better than most scopes. 4 channel scopes usually have just one set of vertical adjustments shared between all the channels.And no scope has independent horizontal adjustment for each channel (apart from a couple really weird ones).

author: tonycstech
author_rank: Regular Contributor
timestamp: June 26, 2023, 12:51:17 am
content: Oh i think i got it.Didnt know it had a trigger source option.But what i see i CH1 or CH2, not both.I dont see the logic here.

author: ataradov
author_rank: Super Contributor
timestamp: June 26, 2023, 12:57:15 am
content: You can't trigger on both. How do you imagine it would work. It need to fix a transition point of a signal at some point. How can you see this working if two channels have different wavefroms?Both signals are always displayed on the same horizontal axis. This is how scopes work. If signals are different, it is impossible to find a point that would be fixed on both at the same time. So, you need to pick which channels is the main trigger channel. The other channels is observed in relation to the trigger channel.

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 01:42:39 am
content: Quote from: ataradov on June 26, 2023, 12:57:15 amWell, technically you could. Trigger on one trace on one sweep then the other trace on the next sweep and display respectively. This was a feature found frequently on better scopes back in the analog days. It seems it's something that could be useful and would be extremely easy to implement on today's mega-smart, bazillion updates per femtosecond, miracle scopes.

author: ataradov
author_rank: Super Contributor
timestamp: June 26, 2023, 01:47:47 am
content: What would be a practical use for this? I have never felt the need for anything like that.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 26, 2023, 01:54:55 am
content: Quote from: ataradov on June 26, 2023, 01:47:47 amLooking at both the head and tail end of a signal without sacrificing horizontal zoom? That's one way to do it when phosphor is the only storage medium onboard.

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 02:00:08 am
content: Just simply monitoring two signals at once. There can be multiple reasons to do this. They could be unrelated but both of interest. They could be related (possibly both suspects in causing a system fault) but not synchronized to each other. They could be signals that have loose synchronization - the approach reduces jitter in the display of certain systems. Monitoring different instruments in a musical piece is a common application I've used in the past.

author: james_s
author_rank: Super Contributor
timestamp: June 26, 2023, 02:04:21 am
content: There could be use cases for this, but most scopes that I've used don't support it, certainly not most budget models, it's a specialized thing. Generally when I want to look at multiple signals at once, I want to see them all in the same context, relative to one another. So maybe I trigger on a clock pulse and I want to see what the data in and data out lines of an interface are doing, or measure the propagation delay of a logic element by probing the input and output. You pick something as the trigger event and then all channels start sampling from the same point. That's just how (most) scopes work.

author: ataradov
author_rank: Super Contributor
timestamp: June 26, 2023, 02:04:48 am
content: Quote from: ArdWar on June 26, 2023, 01:54:55 amThere is a lot of crazy stuff they did when scopes could not store stuff. This is not a problem anymore.The rest sounds too marginal. It would not be too hard to implement, but I can absolutely see why manufacturers don't bother in a general purpose instrument.

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 02:22:53 am
content: Quote from: ataradov on June 26, 2023, 02:04:48 amI have to disagree. I quite often need to look at two things at once. Having to set up nad monitor two scopes is a PITA that quite frankly not everyone has the luxury of. If I have the time to gaze and BW is not an issue I have used my trusty Tek 465, but think how sweet it would be to use my SDS2504X+ and have the history to look back on?To each their own use case, I guess.

author: tonycstech
author_rank: Regular Contributor
timestamp: June 26, 2023, 02:49:58 am
content: I have to look at two things at once to make sure the phase shift is correct between the two.I think this scope does what i need, i just have not played around with it to see how i did it at one point in the past.Thank you.

author: ataradov
author_rank: Super Contributor
timestamp: June 26, 2023, 03:11:27 am
content: Quote from: tonycstech on June 26, 2023, 02:49:58 amYou only need to trigger on one channel for that. The other channel will be stable automatically if the phase shift is constant. This is a very typical use.

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 03:24:50 am
content: Quote from: tonycstech on June 26, 2023, 02:49:58 amYes, As ataradov said, this is a normal application for a scope unless your two signals are not really related. The screen shots you showed would seem to indicate that they are not. You'll probably need to view them independently or try to enable both channels at the same time and trigger on one of them. For now it's not critical which you apply the trigger to. Once you can see both traces at the same time we can help you deicide which needs to be the one where the trigger is placed.

author: radiolistener
author_rank: Super Contributor
timestamp: June 26, 2023, 03:32:25 am
content: Quote from: tonycstech on June 25, 2023, 11:36:35 pmMost of all you're forgot to switch trigger source from CH0 to CH1...

author: tonycstech
author_rank: Regular Contributor
timestamp: June 26, 2023, 06:00:05 am
content: So i tried again, connected to two different sources.This is a GPU. Checking for phase shift.Cannot tell what i am looking at. Only one channel is visible while another is all noise.Unless i change trigger to CH2 i will get a signal, but i need to see both. Otherwise why did i buy 2 channel scope ?

author: ataradov
author_rank: Super Contributor
timestamp: June 26, 2023, 06:02:05 am
content: There is no consistent phase shift here. The signals are not stable relative to each other.Phase shift of what relative to what you are checking?You buy 2-channel scope exactly for this - to see 2 signals at the same time. This is how those signals look in real life.If you want to see instantaneous relation, then you need to use a single shot trigger. It would capture one time and stop. You will see both signals at the same time. As they were at the time of triggering.

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 06:04:54 am
content: Quote from: tonycstech on June 26, 2023, 06:00:05 amThese are not the signals you displayed earlier. Perhaps you need to ask different questions.What different sources did you connect to?As has been presented here, only interdependent sources can be displayed in a coherent manner with modern scopes.Please answer the question above before completing your response.

author: tautech
author_rank: Super Contributor
timestamp: June 26, 2023, 09:56:14 am
content: Quote from: BillyO on June 26, 2023, 01:42:39 amInstead of Alternating trigger found in CRO's, some DSO's have a Pattern/Logic trigger and the OP's certainly has.With careful use of time and trigger levels and a logic AND trigger you can get a stable display allowing measurements to be taken.Below captured with SDS1104X-E.