Rigol DS1054Z New Problem - Page 1
Forum section: electronics / testgear

author: avvidclif
author_rank: Regular Contributor
timestamp: January 17, 2015, 06:32:30 am
content: I started using my 'scope today on the bench. Also using a Tek 2465B. I have to build up the confidence factor in a new piece of equipment so bear with me. Very little digital stuff mostly analog.All was going well and it responded as expected on several different measurements. I noticed a lag in the displayed signal when adjusting the circuit. That I guess I can live with. Aggravating but not real time like the 2465. Then I looked at another test point and decided to try the "Auto" setup. It set up and showed a nice sine wave. The freq counter showed ~83 MHz. All Ok. The Vertical peak measurement was on and showed 520mv. For some reason I moved my hand over the top of the scope and noticed a change. I then tried moving my hand around the top of the 'scope. At ~6" above the scope all was well. As I moved my hand down toward the top of the scope the level dropped to 480mv when my hand was just above the scope. I checked everything around and made sure it wasn't something moving the probe etc. I could put my palm over the top of the scope and vary the displayed level from 520 to 480mv depending on how close my hand was to the top of the scope. I wasn't moving anything but my hand. I didn't try a signal generator directly into the scope and see what happened. This kinda had me scratching my head.Any thoughts???

author: Wytnucls
author_rank: Super Contributor
timestamp: January 17, 2015, 06:37:20 am
content: Electric field? Try grounding yourself next time. Does it make a difference?

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 17, 2015, 06:38:21 am
content: Post a picture of your setup. Are you sure you are not "coupling" with your board under test? What impedance the test point is?

author: c4757p
author_rank: Super Contributor
timestamp: January 17, 2015, 06:39:16 am
content: It's the peak - you are injecting a bit of noise and it sees it. Functioning as intended.

author: Wytnucls
author_rank: Super Contributor
timestamp: January 17, 2015, 06:55:27 am
content: May not be the reason for the fluctuations, but why are you measuring an 83MHz signal with a 50MHz bandwidth scope?

author: Leadfootin
author_rank: Contributor
timestamp: January 17, 2015, 12:54:56 pm
content: Both my DS1074Z and my old Tectonics scopes exhibit the same behaviour due to e-fields, just more apparent on the Rigol due to greater sensitivity. Check out the interference caused by the new high efficiency fluorescent tubes, you can see it with a probe in the air from 5 feet away.At one house I had to conclude any hf experiments before about 9:00 pm when a local ham radio operator lit up his rig.

author: avvidclif
author_rank: Regular Contributor
timestamp: January 17, 2015, 07:32:47 pm
content: Quote from: Wytnucls on January 17, 2015, 06:55:27 amBecause it's been modded.On the interference; the radio I was working on was flat on the bench and the scope hooked to a test point made for adjusting max level. After noticing it I backed away from the radio and tried just my hand over the scope, same thing.I just tried using a signal generator. 50 MHz, -10 dBM into a 50 ohm load on scope. 1m RG58 cable with BNCs.Using Auto setup it showed 655 mV RMS and my hand has no effect anywhere around the scope. I'm guessing the supplied probe cable doesn't have very good shielding and I was close enough to affect it, abt 6-8 inches, scope connection to top of scope, arm parallel to cable.Oh well since none of what I do requires absolute measurements it's not a big deal, just strange.

author: devanno
author_rank: Regular Contributor
timestamp: January 17, 2015, 07:50:17 pm
content: These new digital 'scopes are very sensitive indeed. I set up one in the field to take a measurement and someone turned on the fluorescent overhead light... the noise on the screen was quite amusing... once the lamps warmed up, that noise level diminished significantly. Later, we picked up what appeared to be a CW transmission in the noise... fortunately, these signals were outside the frequency range of what I was interested in looking at, so avoidable. But I can get some interesting signals just by waving a probe around in the air. Eddy indeed.

author: wraper
author_rank: Unknown
timestamp: January 17, 2015, 08:14:11 pm
content: Quote from: avvidclif on January 17, 2015, 07:32:47 pmNothing wrong with the shield. First of all, you need to eliminate the alligator clip ground loop when measuring such frequencies.

author: Bud
author_rank: Super Contributor
timestamp: January 17, 2015, 08:28:21 pm
content: Quote from: avvidclif on January 17, 2015, 06:32:30 am"Confidence in Rigol" is an oxymoron to me.

author: avvidclif
author_rank: Regular Contributor
timestamp: January 18, 2015, 12:04:27 am
content: Quote from: Bud on January 17, 2015, 08:28:21 pmMy 2465B and 475A are not going anywhere.

author: wraper
author_rank: Unknown
timestamp: January 18, 2015, 12:24:31 am
content: This have nothing to do with scope or probe quality. This is about how you measure it. For this reason there are included springy things for the probes which should be used instead of long alligator clip. Or need to make another low inductance ground connection.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 18, 2015, 12:41:56 am
content: To get confidence,buy lecroy or rohde&swaczh.

author: wraper
author_rank: Unknown
timestamp: January 18, 2015, 01:05:54 am
content: Quote from: Mechatrommer on January 18, 2015, 12:41:56 amBut sell your kidney first. Edit: and not low end Siglent rebadge.

author: wraper
author_rank: Unknown
timestamp: January 18, 2015, 01:20:10 am
content: One more thought, As you were moving hand around the scope when this happened, probably it was not properly grounded (old house with crap wiring) in addition to probe ground loop.

author: Nerull
author_rank: Frequent Contributor
timestamp: January 18, 2015, 04:18:57 am
content: Quote from: Mechatrommer on January 18, 2015, 12:41:56 amNone of which will fare any better if you're not probing correctly.

author: pickle9000
author_rank: Super Contributor
timestamp: January 18, 2015, 04:39:05 am
content: Quote from: Mechatrommer on January 18, 2015, 12:41:56 amThis is a bit of a jab, Lecroy low end is a Siglent, and they may be very sorry for helping Siglent out. I'm not knocking Siglent they make some very good scopes.In any case as I always say. All scopes have issues regardless of price, know your equipment limitations / issues and your own.LeCroy Waveace 112ATTEN ADS1102CM

author: Bud
author_rank: Super Contributor
timestamp: January 18, 2015, 06:35:34 pm
content: Quote from: Mechatrommer on January 18, 2015, 12:41:56 amYes, just bought a 20 years young HP spectrum analyzer, no waking up at night worrying about confidence and should be good for another 10 years. Imagining that we'd be still using Rigols 10 years from now is a joke.

author: wraper
author_rank: Unknown
timestamp: January 18, 2015, 06:57:09 pm
content: Quote from: Bud on January 18, 2015, 06:35:34 pmI would have zero confidence in 20 yo test equipment regardless of brand unless I was in call lab very recently.

author: Rupunzell
author_rank: Frequent Contributor
timestamp: January 18, 2015, 07:55:14 pm
content: For working at 100 Mhz, those probes are gigantic!The resistor at the end of the coax will help damp cable reflections, the resistor also limits actual bandwidth of the set-up in the process. The results are actually a complex impedance at the probe tip. It takes more than just connecting the shield directly to the DUT, the ability of the device being probed to drive the load must be considered. In this case, the DUT is being asked to drive the coax and input of the scope, rather complex load. Ponder how this loading affects the DUT and overall test set up?A few pF at 100 Mhz can be significant loading which can significant alter the results.The better would be to use an active probe with known impedance at the probe tip and a probe tip socket properly connected at the test point.This is all good basic measurement practice.BerniceQuote from: wraper on January 18, 2015, 12:24:31 am

author: Rupunzell
author_rank: Frequent Contributor
timestamp: January 18, 2015, 08:02:31 pm
content: Broadcast into the DSO and see what it's reaction might be.Then measure the common mode noise and current from the power ground coming out of it's power cord using a HF transformer (Few turns of the power cord for the primary, few turns for the secondary with a proper termination network for the secondary matched to the scope input on a toroidal soft ferrite core for CMR) and a current probe on the power ground wire with your Tek 2465B.Stuff built with switching power supplies can dump a LOT of HF noise in the form of current into the power mains. This current can show up in everything plugged into the power mains once it finds a return path. and.. it does not show up easy as a voltage measurement.BerniceQuote from: avvidclif on January 17, 2015, 06:32:30 am

author: wraper
author_rank: Unknown
timestamp: January 18, 2015, 08:17:23 pm
content: Quote from: Rupunzell on January 18, 2015, 07:55:14 pmThis was said about why he sees difference in amplitude when moving his hands, not about if passive probe impedance will affect DUT (of course it will). Your comment is irrelevant.

author: jbryan2
author_rank: Contributor
timestamp: January 18, 2015, 08:38:00 pm
content: Quote from: wraper on January 18, 2015, 06:57:09 pmUntil a couple of years ago I was still using a Hewlett-Packard 4194 Impedance Analyzer and it was a fine laboratory-grade instrument after almost 30 years of service. A refurbished one will still set you back around $10k. But it did get the occasional trip to the Cal Lab. I transferred to a different department, but as far as I know it's still in service.

author: wraper
author_rank: Unknown
timestamp: January 18, 2015, 08:53:44 pm
content: QuoteOld equipment can be very good and more stable than a new. But it needs to be checked to be within spec.