SDG1025 setting a DC output? - Page 1
Forum section: electronics / testgear

author: v8dave
author_rank: Regular Contributor
timestamp: April 26, 2016, 05:52:24 am
content: I am having some issues understanding how to setup a DC pulse output on my SDG1025I want a 5V signal to trigger a TTL input. I set the SDG1025 to HLEVEL 5.0 and LLEVEL 0 but I get the attached on the output captured on the scope. I have set the cursors to mark the 5V levels.This shows a 10V signal with a -2.5V offset.The manual doesn't explain anything on how to do this. I can mess around with the values and get something that works but I was just wondering what the actual settings are for something like this as it would be nice to do quick setup without having to hook up the scope (although to be on the safe side, I will probably do this each time anyway)

author: nctnico
author_rank: Super Contributor
timestamp: April 26, 2016, 06:21:21 am
content: You may have set the output impedance to something else than high-Z.

author: v8dave
author_rank: Regular Contributor
timestamp: April 26, 2016, 06:23:19 am
content: Quote from: nctnico on April 26, 2016, 06:21:21 amI get the exact same output with 50R or High-Z.

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2016, 06:39:01 am
content: Quote from: v8dave on April 26, 2016, 06:23:19 amYou will if not terminated into 50 ohms.Sorry gotta run out for a few hrs, will sort this for you when I'm back in ~ 3 hrs.Check for Offset settings is all I can think of ATM.

author: v8dave
author_rank: Regular Contributor
timestamp: April 26, 2016, 07:56:51 am
content: I think it might be related to this as I did do this when I got the unit once it had been running for 30 mins in my workshop?https://www.eevblog.com/forum/repair/siglent-sdg1025-self-cal-failure/Watching the output on the scope it does not change as expected.I need to find out how to reset this.Should anything be connected during the self calibration? Nothing is documented in the manual and I don't see the OUTPUT LED's come on either.

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2016, 10:28:30 am
content: Quote from: v8dave on April 26, 2016, 07:56:51 amDoes your unit show the full SN# or is it the same as in the linked post? ^^^In answer to your question on "Self Adjust", the outputs are not enabled during the procedure and the unit's parameters are checked against internal values.I've not ever seen one fail, does yours offer any error messages?

author: tautech
author_rank: Super Contributor
timestamp: April 26, 2016, 10:59:15 am
content: Anyways, I've linked Tech support to this thread but it's after hours now in Shenzhen so let's see what they can offer tomorrow.

author: v8dave
author_rank: Regular Contributor
timestamp: April 26, 2016, 12:12:14 pm
content: Serial number is fine. Just the vertical issue. Frequency or pulse width changes work.I also contacted the Siglent guy who sends out emails to me and he has copied my email to the support person so if I get anything here I will post back if there is a fix etc.

author: v8dave
author_rank: Regular Contributor
timestamp: April 26, 2016, 11:36:14 pm
content: I powered up the unit this morning and it was still the same so I then ran the self cal without waiting. Now the outputs are working properly again.I then left it for 20 mins and tried the cal again. Now the outputs where all wrong again. Wish I had left it aloneIt doesn't seem to like being warmed up and tested. My workshop is not cooled by AC so is around 28 deg C at this time in the morning. Daytime is around 34 deg C.

author: tautech
author_rank: Super Contributor
timestamp: April 29, 2016, 07:31:24 am
content: Quote from: v8dave on April 26, 2016, 11:36:14 pmDoes this unit still have problems or has further self cals rectified the problem?

author: v8dave
author_rank: Regular Contributor
timestamp: April 29, 2016, 07:51:45 am
content: Quote from: tautech on April 29, 2016, 07:31:24 amThe self cal on power up first thing in the morning fixed the jumping around issue but I still don't see how the relationship of HLEVEL and LLEVEL work.Eg. LLEVEL 0.000 and HLEVEL 5.000 and the scope shows a 10V P-P signal. Set HLEVEL to 2.5 and I now get a 5.0V P-P signal.

author: rf-loop
author_rank: Super Contributor
timestamp: April 29, 2016, 09:45:35 am
content: Quote from: v8dave on April 29, 2016, 07:51:45 amHave you set SDG for Hi-Z or 50ohm or other load impedance.If your scope input is 1M and if your SDG is set for 50ohm you get around double on scope screen, of course.If you connect SDG to scope high impedance (1Mohm) input you need set SDG level for Hi-Z and nothing else.SDG output impedance is always 50ohm, independent of if you have set it for Hi-Z or 50ohm or example 1kOhm.SDG output impedance set match your SDG display levels for match your load impedance. If You set SDG for 50ohm and your LOAD connected to SDG output is 50ohm voltaage over your LOAD is same as your SDG dislay show.This is well exapleined in User Manual.If this do not work, your unit have some failure.Remember, SDG output setting is LOAD setting, it do not set its internal output source impedance!Internal output impedance is always 50ohm including also DC.

author: v8dave
author_rank: Regular Contributor
timestamp: April 29, 2016, 09:53:40 am
content: Quote from: rf-loop on April 29, 2016, 09:45:35 amI see what happens now. The voltage shown on the SDG changes depending on the load setting. I hadn't spotted this until now.If I set to 50ohm it shows HLEVEL as 2.5V and if I set to High-Z it shows 5.0VThanks for pointing me in the right direction. Now I can go play with more confidence.Appreciate your time on this.Dave...

author: rf-loop
author_rank: Super Contributor
timestamp: April 29, 2016, 10:12:29 am
content: Quote from: v8dave on April 29, 2016, 09:53:40 amEdited my last msg. (more info)

author: tautech
author_rank: Super Contributor
timestamp: April 29, 2016, 10:30:32 am
content: Quote from: v8dave on April 29, 2016, 09:53:40 amInteresting....reply #2Quote from: v8dave on April 26, 2016, 06:23:19 amWhat's changed?

author: v8dave
author_rank: Regular Contributor
timestamp: April 29, 2016, 11:53:20 am
content: Quote from: tautech on April 29, 2016, 10:30:32 amMe not paying attention to the fact that the SDG changes the values when you change from 50 ohm to High-Z. It shows 2.5 for 50 and 5.0 for High-Z. I never spotted this as I was always using it with 50 ohm setting.

author: rf-loop
author_rank: Super Contributor
timestamp: April 29, 2016, 02:17:23 pm
content: Perhaps this image can clarify it bit more also for some other users.Augmented picture is based on the SDG1000 series User Manual page 67.(for R Load values over 10k ~20k use Hi-Z.If your load is under 50 ohm you can use set value Hi-Z and calculate. (Hi-Z value can think as G voltage in image)Example, if your load is 35 ohm and Hi-Z output is 2V. (in image, G output) after then you have now internal 50 ohm and your Load 35 ohm in series. Load voltage: 35/(35+50)*2= 0.82V(normally SDG1000 do this calculation for displayed Voltage but there can not set under 50 ohm load values)