A good digital oscilloscope?
in [Design]
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From: qrk on 8 Dec 2009 15:29 On Tue, 8 Dec 2009 06:11:02 -0800 (PST), George Herold <ggherold(a)gmail.com> wrote: >On Dec 7, 2:56�pm, qrk <SpamT...(a)spam.net> wrote: >> On Sun, 06 Dec 2009 20:29:24 -0800, John Larkin >> >> >> >> >> >> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >On Sun, 6 Dec 2009 22:18:04 -0600, "Tim Williams" >> ><tmoran...(a)charter.net> wrote: >> >> >>I never was too impressed with digital scopes. �None of them have nearly >> >>enough buttons, so you spend all your time wading through menus. �The Rigol >> >>I've used (don't remember the number) has awful menus, they are not always >> >>quite what they say they are, and they take forever to go away. >> >> >>Some digital scopes have better refresh than others. �The HP (Agilent??) >> >>54622D's in all the labs at school here work fairly well, though at least >> >>two button presses are required to reach any given menu option. �Refresh is >> >>okay, though still chunky on slower sweeps (>1ms/div). >> >> >>My impression of the cheapass Tek TDS's (the thin rectangular ones) is >> >>similar to the Rigol. >> >> >>I'm most familiar with my Tek 475, but it would be nice to have storage, >> >>single sweep* and averaging. �One of those intermediate scopes, the ones >> >>with analog AND digital, they're perfect for everything. >> >> >>*Just because it's an analog scope doesn't mean you don't get storage or >> >>single sweep type readings, it just means it takes more setup. �This >> >>photograph was taken with a 10 second exposure, capturing three photoflash >> >>discharges: >> >>http://webpages.charter.net/dawill/Images/Photoflash_Discharge2_sm.jpg >> >> >>Tim >> >> >I like my TDS2012. I rarely use an analog scope any more. >> >> >John >> >> I find that I use an analog scope (Tek 465) for analog stuff. Can't >> get a feeling for noise issues with a digital scope. For pulse >> amplifier stuff and when you need arithmetic, digital is the way to >> go. >> >> -- >> Mark- Hide quoted text - >> >> - Show quoted text - > >Not sure what sort of noise you are looking at, but I love my digital >�scope for looking at noise. The trick I use is to trigger right up >at the top of the noise. Then I put the scope in average mode and you >get an image that looks like the auto correlation function. My >colleague has dubbed this the Quasi � auto- correlation function, >�Quacf� for short and of course pronounced quaff. (Ahh, nothing like >a good beer.) If you ask for the FFT of this �trace� you get a much >better picture. But I�ve become very good at reading quacf�s. > >George H. > I deal with high gain amplifiers (80 dB gain, around 256 channels per system) sitting in a sea of noise. Trying to pick out switching power supply noise, digital noise, AM & FM radio transmitters, and ground loop noise from other equipment is difficult with digital scopes since the structure of the noise is lost. I'll revert to frequency domain (usually a swept analyzer) to pick out the offending frequency if it's from a switcher, clock or radio station, but logic noise doesn't show up well in the frequency domain. The sweep rep rate of digital scopes is better than days of yore, but still not as good as a 30 year old 465 which puts digital scopes at a disadvantage when looking at noise structure. Plus, the alias factor of digital scopes is misleading - so much so, that I'll use one of my analog scopes to figure out what the real waveform looks like so I can set up the digital scope or understand why I'm seeing odd looking signals. Not that I'm anti-digital scope, I just like using the tool that makes the task at hand easier to deal with. -- Mark
From: Nico Coesel on 8 Dec 2009 15:32 George Herold <ggherold(a)gmail.com> wrote: >On Dec 7, 2:56=A0pm, qrk <SpamT...(a)spam.net> wrote: >> On Sun, 06 Dec 2009 20:29:24 -0800, John Larkin >> >> >> >> >> >> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >On Sun, 6 Dec 2009 22:18:04 -0600, "Tim Williams" >> ><tmoran...(a)charter.net> wrote: >> >> >>single sweep* and averaging. =A0One of those intermediate scopes, the o= >nes >> >>with analog AND digital, they're perfect for everything. >> >> >>*Just because it's an analog scope doesn't mean you don't get storage o= >r >> >>single sweep type readings, it just means it takes more setup. =A0This >> >>photograph was taken with a 10 second exposure, capturing three photofl= >ash >> >>discharges: >> >>http://webpages.charter.net/dawill/Images/Photoflash_Discharge2_sm.jpg >> >> >>Tim >> >> >I like my TDS2012. I rarely use an analog scope any more. >> >> >John >> >> I find that I use an analog scope (Tek 465) for analog stuff. Can't >> get a feeling for noise issues with a digital scope. For pulse >> amplifier stuff and when you need arithmetic, digital is the way to >> go. >> >> -- >> Mark- Hide quoted text - >> >> - Show quoted text - > >Not sure what sort of noise you are looking at, but I love my digital >=91scope for looking at noise. The trick I use is to trigger right up >at the top of the noise. Then I put the scope in average mode and you The TDS220 at work has terrible noise. My Tek2230 does much better. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... "If it doesn't fit, use a bigger hammer!" --------------------------------------------------------------
From: Jim Yanik on 8 Dec 2009 15:38 "Tim Williams" <tmoranwms(a)charter.net> wrote in news:hfm64q$k3h$1(a)news.eternal-september.org: > "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in > message news:oh6th5903d58sogu3cj8vk3er6r6li9m32(a)4ax.com... >> I love our TPS2024. 200 MHz, and all four channels and the trigger >> input are fully floating. Wanna clip the probe ground lead onto the >> source of a fet that's flailing 400 volts off ground? No problem. > > Tasty. > > What's C-to-ground like, is it basically a differential input (2 x 1M > || 20pF) with a BNC input? > > Tim > it's probably just a isolated power supply and isolation from the cabinet. differential inputs are more expensive to implement. Did you see my earlier post about TEK moving production to China? also,TEK has bought Sypris Test & Measurement,a third-party supplier of repair and calibration services;so it appears they're trying to re- establish the service centers they USED to have around the US,but closed the last of them back in 1999. It only took them TEN years this time to learn they messed up closing local service centers..... Danaher really needs to "clean up" TEK T&M management.(clean OUT) Those guys never did have a clue about service. All they know is Beaverton and the factory environment. Hmm,kinda like our politicians in DC today... -- Jim Yanik jyanik at localnet dot com
From: John Larkin on 8 Dec 2009 16:13 On Tue, 08 Dec 2009 19:09:03 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Tue, 08 Dec 2009 10:58:50 -0800) it happened Joerg ><invalid(a)invalid.invalid> wrote in <7o7lveF3obbsiU2(a)mid.individual.net>: > >>>>> ftp://panteltje.com/pub/DVD_remote_fluorescent_buttons_img_1676.jpg >>>> Try some strontium aluminate. It's something like 10x better a light >>>> storage thing than the old ZnS stuff. >>>> >>>> John >>> >>> The DVD remote in the above link *is* strontium aluminate, >>> I just did the 4 minute test, >>> http://en.wikipedia.org/wiki/Phosphorescence (scroll down) >>> still clearly visible, not adapted eyes, also after 5 minutes. >>> The color also matches tha tbird... >>> They say the ZnS stuff is no longer used... >>> The real 'hot' stuff I remember from my youth was 'radium', >>> radium on watches, clocks, and even on some light switches. >>> That was all no longer allowed at some point. >> >> >>Back in those days watch dials would be readable all night, not nearly >>have that much decay. That is no longer the case, no matter what fancy >>material they use. > >No problem, you can have it if you want: >Tritium: > http://en.wikilib.com/wiki/Tritium >Tritium watch: > http://en.wikipedia.org/wiki/File:Tritium-watch.jpg >Tritium alarm clock: > http://www.ultralux.ch/de_shop.cfm?cmd=detail&id=48&pid=142¤t=1&mainkat=5 I put tritium lights on the tops of the bedposts in the cabin... it's really dark up there, and you can whack yourself in the head coming back from peeing. I had to order them from England, as I think they are illegal in the USA. ftp://jjlarkin.lmi.net/Tritium.jpg John
From: John Larkin on 8 Dec 2009 16:15
On Tue, 08 Dec 2009 14:36:53 -0500, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >On Tue, 08 Dec 2009 10:28:27 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Mon, 7 Dec 2009 22:21:43 -0600, "Tim Williams" >><tmoranwms(a)charter.net> wrote: >> >>>"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in message >>>news:oFhTm.36236$kY2.31856(a)newsfe01.iad... >>>> My Tek 485 serves me well. I do have a small assortment of digital scopes >>>> for portable use to gather basic data and road trip testing how ever, I >>>> find that my 485 still gives me nice results at the bench as long as I >>>> don't need live digital storage. >>>> It's the only scope I have that I can take full advantage of my active >>>> Fet probes when I need them. >>> >>>486 is on my Wish List. And 2465. Yessss, my preciousss.... >>> >>> >>>Tim >> >>I love our TPS2024. 200 MHz, and all four channels and the trigger >>input are fully floating. Wanna clip the probe ground lead onto the >>source of a fet that's flailing 400 volts off ground? No problem. >> >>John > >Shame about that antediluvian CF card slot that can't write to even a >2G card. 8-( Just snap a photo of the screen. John |