Got myself a free scope. Have questions. - Page 1
Forum section: electronics / testgear

author: Jckf
author_rank: Newbie
timestamp: December 06, 2014, 05:00:22 pm
content: Hello, fellows. I recently got my first oscilloscope for free from a guy in my local hackerspace! It's a Kenwood CS-1045 2 ch. 40 MHz analoge scope, and it appears to be in 100% working orderThe only question I have (so far) is whether or not the calibration is still good. It has an integrated 1 kHz generator, and when hooked up to it and set to 1v/0.5ms per division, the attached image is what I see. Shouldn't each duty cycle correspond to exactly 2 divisions?EDIT: Oh, one more thing! Does anyone have the service manual for this?EDIT 2:Figured it out! The red knob together with the sweep time adjustments is for calibration

author: tggzzz
author_rank: Super Contributor
timestamp: December 06, 2014, 06:17:54 pm
content: The purpose of the 1kHz square wave is to allow you to tweak the compensation of *10 probes. The frequency and amplitude are relatively unimportant - all that matters is that the transitions are smooth, fast, and there is no over/undershoot.Don't use it to calibrate the voltage nor time.

author: radhaz
author_rank: Regular Contributor
timestamp: December 06, 2014, 06:21:16 pm
content: https://www.eevblog.com/forum/beginners/oscilloscope-training-class-%28long%29/

author: Jckf
author_rank: Newbie
timestamp: December 06, 2014, 06:55:08 pm
content: This is how it looks now:Quote from: tggzzz on December 06, 2014, 06:17:54 pmExactly why is this a bad thing?Quote from: radhaz on December 06, 2014, 06:21:16 pmThank you. I will watch this

author: tautech
author_rank: Super Contributor
timestamp: December 06, 2014, 07:10:28 pm
content: Quote from: Jckf on December 06, 2014, 06:55:08 pmThe Cal output is neither precise or accurate enough for scope timebase or amplitude adjustments.In your case it represents only 1/40,000thof the bandwidth of your scope.Astggzzzsays it is only intended for adjustment of probes.BTW good score on the free scope.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 07, 2014, 01:33:52 am
content: Quote from: Jckf on December 06, 2014, 05:00:22 pmErr, no it's not. The red knob has a detent position all the way clockwise. At that position the timebase is supposed to be calibrated. Same for the channel gain red knobs.Any other position, is variable, ie the scope timebase/gain is uncalibrated. It's useful for lining up traces with the graticule to judge proportional amplitudes of waveform features. But in 'uncal' mode you can't use the graticule to measure absolute amplitude/time.For accurate calibration, you need an external known signal. As mentioned by others that 'cal' output is really only for adjusting probe compensation.Nice scope btw. Have fun!

author: Jckf
author_rank: Newbie
timestamp: December 07, 2014, 08:43:52 pm
content: Quote from: tautech on December 06, 2014, 07:10:28 pmOf course. This makes a lot of sense. I guess the manual will tell me exactly what I need to know.Quote from: TerraHertz on December 07, 2014, 01:33:52 amI thought having the calibration on the front of the scope was weird, and the knob snaps into position all the way to the right, just as you describe, which made we wonder.EDIT: I have probed an external signal, and found that the calibration is spot on! This must mean that the generator in the scope is really bad!EDIT 2: Looks like the 1 kHz generator in the scope is closer to 930 Hz

author: Rigby
author_rank: Super Contributor
timestamp: December 08, 2014, 10:38:10 pm
content: Sounds about right to me. I've never seen a probe compensation signal that was right OK 1kHz.

author: PaulAm
author_rank: Frequent Contributor
timestamp: December 08, 2014, 11:01:46 pm
content: The Tek 454 (and 453) had a calibration adjustment for calibrator frequency, but not amplitude. That's the only one I know of that did that. Most Tek scopes had an internal amplitude adjustment so you could set the calibrator output to a known value. That way you could do a sanity check on your probe, as well as compensation adjustment. Many Tek scopes also provided a current calibration so you could check a current probe with a more or less known current source.But timing reference? If they're within +/- 100 Hz that's in the ballpark. The calibrator circuits are generally pretty simple oscillators or multivibrators.

author: tautech
author_rank: Super Contributor
timestamp: December 08, 2014, 11:30:12 pm
content: Quote from: PaulAm on December 08, 2014, 11:01:46 pmOn the scopes I have fixed, I have always endeavoured to get the Cal output as close as possible to spec with another scope WHEN internal adjustment allows it.Many old scopes allowed for both Frequency & Amplitude to be adjusted and others only one.It just makes sense to have them both close for sanity's sake IMO.

author: vk6zgo
author_rank: Super Contributor
timestamp: December 09, 2014, 03:56:31 am
content: Quote from: TerraHertz on December 07, 2014, 01:33:52 amA little further comment on the "Uncalibrated" mode:-This comes up a lot with people buying their first analog Oscilloscope.The Uncalibrated setting is,for working Techs,one of the most useful functions of such a 'scope.As TerraHertz so correctly points out,it enables us to easily compare amplitudes of different parts of signals.Say we want to express one voltage as a percentage of another one.:-We could measure both, then grab a calculator & work it out,--OR--we could adjust the larger one to represent 100% & read percentage directly off the scale.Many test procedures,particularly in TV Broadcasting used special graticules,either physically placed in front of the screen,or "Projected".These had "reference points"forboth time & amplitude,which rarely coincided with the calibrated settings & had to be set in the "Uncalibrated" position.