Calibrating an Oscilloscope - Page 1
Forum section: electronics / beginners

author: Mati256
author_rank: Contributor
timestamp: October 15, 2014, 02:30:13 pm
content: Hello, I recently bought a Hitachi V212. I have some basics on how to operate an oscilloscope, I have made a Variable Power Source and checked it with an oscilloscope before. But the truth is I don't fully know how to use them.I'm triying to calibrate this one and I'm geting a 20mv (more like an 18-19mv) square wave. Now, the cal. value of this one is .5V so I'm assuming I should get a .5V square wave?If I set the Volt/Div to .5 I only get an almost linear wave.Please tell me this can be fixed in a simple way.Thanks!

author: oldway
author_rank: Super Contributor
timestamp: October 15, 2014, 02:41:31 pm
content: Easier to calibrate the vert. gain with DC voltage using a power supply with a voltage divider and a multimeter than with an AC wave.For AC compensation of input attenuator, better not to try to calibrate it if you don't have experience and don't have a really good function generator with a BNC 50R load.

author: Mati256
author_rank: Contributor
timestamp: October 15, 2014, 03:01:05 pm
content: So as I suspected, and seemed obvious, it is not calibrated correctly. I will take it somewhere to calibrate it then.Thanks!EDIT: I have checked with my electronics store and they don't do it. Will keep searching.

author: grumpydoc
author_rank: Super Contributor
timestamp: October 15, 2014, 03:11:20 pm
content: QuoteThe "calibration" output is only really there for setting probe compensation.However if you really are getting only 18-20mV for a squarewave which should be 0.5V, it isn't a calibration issue - there is a fault somewhere.More details might help. How have you got the 'scope set up? Did you use a probe to measure the calibration signal if so was it in x1 or x10, have you tried both channels? Do you have access to another 'scope to check whether it is the squarewave output which is at fault?

author: Mati256
author_rank: Contributor
timestamp: October 15, 2014, 03:49:16 pm
content: Quote from: grumpydoc on October 15, 2014, 03:11:20 pmWhat do you mean by set up?I used an at 10aj probe, I think is the original one, I'm assuming its an x1 because it does not have an option between x1 and x10.I have tried both channels with the same results.I don't hace access to another oscilloscope.Measuring a 9v battery gives a value of around .2 volts.

author: grumpydoc
author_rank: Super Contributor
timestamp: October 15, 2014, 04:12:03 pm
content: QuoteSounds like there is a fault, then.

author: tommydyhr
author_rank: Contributor
timestamp: October 15, 2014, 05:55:18 pm
content: This does indeed possibly sound like a faulty amplifier-stage. That much deviation can certainly not be calibrated.QuoteThis is never a safe assumption. Many probes are fixed x10. Fixed x100 high voltage probes are quite common as well.

author: grumpydoc
author_rank: Super Contributor
timestamp: October 15, 2014, 06:16:03 pm
content: QuoteIndeed a quick google will show that the Hitachi AT-10AJ probe is a fixed X10 probe.The 9V battery should still show as 0.9V, not 0.2V. Generally a scope which is "out of cal" might be 20% out at worst, not showing about 20% of the correct value.Have you double checked the vertical V/div setting.Have you also checked that the vertical "var" knob is clicked into the "cal" position.

author: Mati256
author_rank: Contributor
timestamp: October 15, 2014, 07:14:51 pm
content: Quote from: grumpydoc on October 15, 2014, 06:16:03 pmOk, I feel quite dumb right now. I have set the "var" (all of them) into the cal position. This position is on the right, in the scope I used before this knob was always to the left, so I assumed there is where it should be.Now, I have measured the 9V battery again and I'm getting 0.9V in the .5V Volts/Div. Is this OK if the probes are X10?Also, with this in mind I have rechecked the calibration thing and now I'm getting a square wave of 50mV, and with the X10 that should be the .5V I'm looking for.Would you say this is ok?Picture attached of the 9V Battery.

author: tommydyhr
author_rank: Contributor
timestamp: October 15, 2014, 07:28:25 pm
content: Quote from: Mati256 on October 15, 2014, 07:14:51 pmYep, that is indeed exactly what you want!

author: tautech
author_rank: Super Contributor
timestamp: October 15, 2014, 07:42:29 pm
content: Quote from: Mati256 on October 15, 2014, 07:14:51 pmNot to worry, most of us have made that mistake at some time.Many scopes had a small red warning light that came on when the Variable knob was moved from the Cal position.Continued use will help with familiarity.Hunt out a manual for future reference and possible repair.

author: Mati256
author_rank: Contributor
timestamp: October 16, 2014, 10:38:39 pm
content: Thank you. This made my day!

author: tggzzz
author_rank: Super Contributor
timestamp: October 17, 2014, 08:47:20 am
content: Quote from: Mati256 on October 15, 2014, 07:14:51 pmFortunately I have never made that mistake. Never ever, oh no. Never ever wasted hours of my time like that.Hence I never ever ever warn 'scope newbies about the problem.(http://en.wikipedia.org/wiki/The_lady_doth_protest_too_much,_methinks)

author: grumpydoc
author_rank: Super Contributor
timestamp: October 17, 2014, 03:11:29 pm
content: QuoteOf course not, Malcolm**My usual problem is a slight variation on this. More than once after calibrating and checking a 'scope I've photographed it for ebay only to notice when I do the auction that the var knob wasn't in the "cal" position and had to go back and do the photo's again. This is especially annoying since it's usually close enough not to change the display noticably but I like things to line up properly.** You have to be British and the right age to remember a particular advert for decongestant to understand this reference, I'm afraid.