What Am I Doing Wrong With This 'Scope? - Page 1
Forum section: electronics / beginners

author: ed_reardon
author_rank: Regular Contributor
timestamp: August 05, 2016, 07:48:35 pm
content: Hi all,I've borrowed a Tektronics 2211 (an oldie Google tells me) from work to so some work at home on some small circuits.Now all the signals I've looked for, the amplitude is way off from scale, even on a x1 probe and I've got a suite of probes to try.Now, tell me where I'm being a numpty here!I've set the coupling to DC, and I've used the ground to provide the reference to get the Channel -1 line on the centre graticule, I've tested my accurate DC source at 5V with my calibrated 85V, it's as near to 5V as it'll ever be.It's connected with the straight coax as shown.The line barely moves, I'm getting even less on Channel-2. The 'scope is absolutely doing my head in! It's making tracing signals very very awkward.All have a good point and laugh, here are my settings:You can just see the trace sitting about a line's width above the centre graticule, this is with the voltage source a definite 5V and 1V/Div.Is it me, or is there something else going on?To add, I've got all storage (where there many of these storage CRT 'scopes back in the day?) switched off.Cheers,Ed

author: dfmischler
author_rank: Frequent Contributor
timestamp: August 05, 2016, 08:28:17 pm
content: Make sure the center knob on the "CH 1 VOLTS/DIV" setting is pushed in and twisted all the way to "CAL".

author: DmitryL
author_rank: Regular Contributor
timestamp: August 05, 2016, 08:28:33 pm
content: Have you got "beam find" button pressed in ?BTW, you have "Add" mode ON, i.e scope displays chan1+chan2, not the best idea do start with.What does it show if you use AC waveform from "probe adjust" port ?

author: ed_reardon
author_rank: Regular Contributor
timestamp: August 05, 2016, 09:16:18 pm
content: Cheers guys, it's been a long day and it's set up in the conservatory which doesn't have lights so I've given up fiddling in the dark.Yes, it was the blasted cal knobThe probe is set to only display channel one, I only have options to chop alternate or add so unless I've got this totally arse-backwards provding only one channel is selected that would be bypassed anyway.Oh it's been a long day, tomorrow's a fresh one in daylight eh?Cheers,Ed

author: ovnr
author_rank: Frequent Contributor
timestamp: August 05, 2016, 09:24:38 pm
content: Quote from: ed_reardon on August 05, 2016, 09:16:18 pmAdd is a mode you willveryrarely use; to avoid headaches in the future, I suggest keeping it set to alternate or chop. Yes, with a single channel connected it will do nothing, but you will end up forgetting it's set up this way and it will be a pain in the ass.Incidentally, Chop rapidly switches between drawing A and B at the same time, while Alternate draws channel A then channel B. Alternate is more appropriate to use when looking at high-frequency signals, but offers poor performance at slower timescales.

author: techie1234
author_rank: Regular Contributor
timestamp: August 05, 2016, 11:25:57 pm
content: Quote from: DmitryL on August 05, 2016, 08:28:33 pmYeah, the Beam Find button sure looks like it's pressed in which would explain the behavior.

author: ed_reardon
author_rank: Regular Contributor
timestamp: August 06, 2016, 06:11:21 am
content: Good point but 100% not, this 'scope has a PTM beam find button, it doesn't latch.Have to use it often enough as the damn cursor bars can end up all over the place!Does anybody know a way to recentre the cursors on these by the way?

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2016, 06:59:24 am
content: Quote from: ed_reardon on August 05, 2016, 07:48:35 pmThe first of these types of combined analog and digital storage was the Tektronix 468 produced from 1981 to 1985. It was replaced by the 2230 in 1986 and a whole series of 22xx based combined analog and digital storage oscilloscopes produced from 1986 to 1995. I consider the 2230/2232 and their close cousins to be the first "real" DSOs since they support peak detection.I am not sure about your cursor problem. I have never used the 2210/2211 and they are pretty rare only being produced from 1989 to 1991. I suggest reading the operating manual which is available online and trying the various exercises.

author: ed_reardon
author_rank: Regular Contributor
timestamp: August 06, 2016, 07:03:58 am
content: Quote from: David Hess on August 06, 2016, 06:59:24 amInteresting, as said it's not mine I borrowed it from work from a dusty rack of redundant equipment; it's last calibration according to the stickers was in March 1998.I guess it's an okay 'scope for me to mess about with at home?

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2016, 07:23:09 am
content: Quote from: ed_reardon on August 06, 2016, 07:03:58 amIt is a fine oscilloscope when used within its limitations. Think of it as a 50 MHz single timebase analog oscilloscope which has cursor measurements and basic digital storage. I would consider it a great "learners" oscilloscope.The 2201, 2205, 2210, and 2211 are based on the 50 MHz single timebase 2225 analog only oscilloscope which was a later lower cost design to complement the 100 MHz dual timebase 2235 series which includes the 2230 and 2232 DSOs that I like so much.The 2211 lacks peak detection and equivalent time sampling so its digital storage is pretty primitive but it does have cursor measurements in analog and digital storage mode and it keeps the 5 MHz x10 vertical magnification (500 uV/div sensitivity) of the 2225 which is very handy in some applications like audio and low frequency work. Its 50 MHz bandwidth is sufficient for a majority of design work.

author: danadak
author_rank: Super Contributor
timestamp: August 06, 2016, 12:12:51 pm
content: The add mode very useful in making differential measurements. You choose thatmode, invert channel 2, and use chan 1 & 2 as the differential input. Rejects CMsignals and just looks at normal mode signals. Within the specs of CM rejection.Note probes have to be matched and adjusted properly.Note CMR is a f(frequency) so at higher f you get less CM rejection.Regards, Dana.

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2016, 01:53:56 pm
content: Add and invert mode is fabulous on these oscilloscopes for differential measurements and better then most DSOs doing the same thing because subtracting after quantization on a DSO adds more noise than doing the subtraction in the analog domain and the variable volt/div control can be used to closely match the DC attenuation of the probes and input circuits for best low frequency common mode rejection. AC common mode rejection can be trimmed with the probe compensation adjustments.Add and invert mode however does have a limited common mode range so it is not a replacement for true differential input in all applications.

author: techie1234
author_rank: Regular Contributor
timestamp: August 11, 2016, 01:34:22 pm
content: Quote from: ed_reardon on August 06, 2016, 06:11:21 amGood you found your problem. My thinking was that, even if the button doesn't latch (is there a scope that has a latching beam find button?!?), it might be getting stuck on its travel back out and not fully disconnecting. The power button on my HP 1743A does this - although it is a latching switch in this case, when I push it to turn things off the latch disconnects but then it gets stuck on its way back out. I have to pull it a bit to get it all the way back out and the power to turn off.Another CRO saved from the dumpster!