Wildly incorrect readings on a new SDS1104X-E - Page 1
Forum section: electronics / beginners

author: notlegato
author_rank: Newbie
timestamp: April 17, 2018, 07:51:20 pm
content: Hey, I just got a Siglent SDS1104X-E in the mail from a retailer and it's supposedly been calibrated in January and tested by the seller (mostly stress-testing tbf), butwhile I'm checking it out, I notice that all the voltage readings are *very* off.I'm new to digital oscilloscopes, so I'm not sure if it's something I'm doing, but when measuring a couple batteries, first with a multimeter, then the scope, I got:9.4V on multimeter => first 10.6V on scope, then 12.2V on scope (after enabling channel 2 later).1.4V on multimeter => 1.6V on scope.I'm contacting the seller just in case there is a real issue, but I was wondering if any of you would know if it's just me, or the actual hardware.E: The scope also fails to show the correct frequency in the top right corner, always showing f < 10Hz, though the measure function gives me the correct answer.No idea what that's about...

author: tautech
author_rank: Super Contributor
timestamp: April 17, 2018, 08:03:20 pm
content: Quote from: notlegato on April 17, 2018, 07:51:20 pmWelcome to the forum.Please check the firmware version, it should be 20R1.Siglent scopes don't measure frequencies below 10 Hz in the HW counter. You need set a Frequency measure as you have to do this.Hard to say without screenshots just what's going on.Does the ~3V 1 KHz probe compensation output read correctly ?

author: notlegato
author_rank: Newbie
timestamp: April 17, 2018, 08:08:57 pm
content: No, that was the issue. the 1kHZ signal still shows f < 10Hz in the top corner.and it gives me an amplitude of 3.36V.7.6.1.20 R1 is the current firmware.

author: tautech
author_rank: Super Contributor
timestamp: April 17, 2018, 08:20:07 pm
content: Quote from: notlegato on April 17, 2018, 08:08:57 pmPlease check you have several periods/waveforms displayed on the screen.Amplitude is a nominal 3V so a little high is normal.Add a screenshot as an attachment to a reply as we can get more info that than a discussion just from a glance at it.

author: notlegato
author_rank: Newbie
timestamp: April 17, 2018, 08:25:49 pm
content: Alright, here's one screenshot, at least.Another thing, which I'm not sure if it's a problem or not is that the waveform doesn't roll smoothly, but stops every half a second or so, very consistently. Whether it's just nominal performance or whatever.EDIT: Oddly enough, if I auto-setup it, we get this:

author: tautech
author_rank: Super Contributor
timestamp: April 17, 2018, 08:28:42 pm
content: Quote from: notlegato on April 17, 2018, 08:25:49 pmPress the Trigger level control and it automatically sets the level to 50% of the waveform. This will fix any triggering instability. The level pointer/indicator is the < on the right of the display. You should get an accurate frequency then.

author: notlegato
author_rank: Newbie
timestamp: April 17, 2018, 08:38:00 pm
content: Oh, so I can't have the waveform currently MOVING if I want the frequency to be correctly measured in HW? That's interesting.Well, that worked. Great!Then, what about the inaccuracies with the batteries I measured? 9.4V to 12.2V is kind of drastic....Okay, nevermind. I did my new measurements now, and got 9.94RMS. Still off, but less. No idea why. Used 10X instead of 1X this time.

author: tautech
author_rank: Super Contributor
timestamp: April 17, 2018, 08:43:32 pm
content: Quote from: notlegato on April 17, 2018, 08:38:00 pmSome quick things for you to consider and experiment with and now I must go.The Trigger is the most important and powerful asset in a DSO.Trigger hysteresis.Enjoy.

author: notlegato
author_rank: Newbie
timestamp: April 17, 2018, 08:55:37 pm
content: I've stumbled on something interesting regarding the voltage discrepancy.Look at these screenshots.And here, the same voltage source, with nothing but an adjustment made to the VERTICAL POSITION?This seems promising as a beginning answer to my problem. Adjusting the vertical position of the thing changes the "RMS" stated? If I zero it by clicking the knob, I get 10.4V, which is incorrect, and that's strange.

author: tautech
author_rank: Super Contributor
timestamp: April 18, 2018, 09:19:36 am
content: Quote from: tautech on April 17, 2018, 08:28:42 pmAnother thing about this screenshot.....It appears the probe isn't perfectly compensated so stretch the waveform with a faster timebase setting and adjust the probe to get the tops and bottoms perfectly flat. That will help with measurement accuracy.WRT to you other measurements.....my demo is off being appraised at a customers so I can't check them in greater detail for you. In the next day or so when I do PD checks on a new one I'll try to look at this for you.Now this one:You opened with:QuoteWhich implies you know how to use a scope and if this is so I'd advise you to 'drive' it just as you would any other scope instead of using Autoset.You will get to know your scope better and better understand what you trying to achieve with it and just how to go about it.

author: StillTrying
author_rank: Super Contributor
timestamp: April 18, 2018, 03:47:35 pm
content: As well as the X10 probe compensation do a warmed upself-calibration."I'm new to digital oscilloscopes"You're probably not used to the terribly low DSO Y resolution!Compared with a possible 5999 count DVM, DC wise a DSO scope is only a 199 to 49 count DVM - on a good day!On the 5V/div range the Y resolution is only 0.2V so getting 9.40 and 9.60 is fine. The 12.4V is probably just added noise spikes and mains noise.Try AUTO trigger and about 10ms/div. and spread the amplitude over 5 to 7 high divisions for about the best DC readings.But, the 0V markers seem off a bit.

author: notlegato
author_rank: Newbie
timestamp: April 18, 2018, 04:24:57 pm
content: I've been chatting with the seller- who, I will add, is clearly a VERY knowledgeable professional, and he told me to do the calibration and run some tests for him, andeverything is fixed.Cal signal is basically exact with his, DC measurements are within +/- 1% of multimeter, the works.Good to have a retailer who knows his stuff.Can't believe how big of a difference a small calibration can make- gotta remember to do those every once a while.I also finished my workbench!and it looks great. Got the table for free. Ahh, such a nice space.