Another 'scope question

Thanks all for the info so far. Now another one. The probe is set at
1X. The volts/div is set at 50 m. the time/div is set at .1 ms. So
this tells me that each vertical division is 50 millivolts and each
horizontal division is .1 milliseconds. The probe is clipped to the
calibration bar. This bar is labeled as 300 mV 30mA ~1KHz. The display
shows the square wave with 6 divisions vertical and just over 10
divisions horizontal. Using the VAR knob in the center of the time/div
knob I can adjust the display to show exactly 10 divisions. When this
is done is the display correct? Or is it the calibration bar that is
wrong?
Thanks,
Eric
Reply to
Eric R Snow
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I'd check the calibration with a DVM (you have to assume that is reasonably accurate). Simply put the scope across a 9 V battery, and compare the deflection with the voltage indicated by the DVM.
Leon
Reply to
Leon
Hi Eric, the following website might be of interest to you.
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------------------------------------------------------------- Eric R Snow - Fri, Feb 10 2006 12:58 pm
The display shows the square wave with 6 divisions vertical and just over 10 divisions horizontal. Using the VAR knob in the center of the time/div knob I can adjust the display to show exactly 10 divisions. When this is done is the display correct? Or is it the calibration bar that is wrong? Thanks, Eric
Reply to
Buy_Sell
Once you move the VAR knob off the cal position you have lost the ability to measure time on the X axis or peak voltage on the Y axis.
So in your case you really don't know how long each division is. Put the VAR know back on its detent and select the best scale. Then you can read the period off the X axis. If you vertical knobs are in the cal position you can read the peak voltage off the Y axis.
You really should find a book that shows you how to do this.
Reply to
Chuck Sherwood
Assuming that the time base is correct your scope timebase is off. You should be able to set the sweep knob in the 'cal' position and have the thing line up exactly. There will probably be an internal adjustment.
I'd try to get a manual for that scope, and a time standard that'll give you a second opinion.
Reply to
Tim Wescott
I have ordered the manual. And downloaded a copy from Ig. I am still looking for a book that is all about using oscilloscopes and is aimed at beginners. ERS
Reply to
Eric R Snow
The time division is correct only when the VAR knob is clicked off.
GWE
Reply to
Grant Erwin
Your vertical sounds right. Either your reference calibrator, your sweep timebase or your horizontal gain is off a tad. If you set the variable timebase to show exactly 10 divisions, then the horizontal scale really is 0.1 ms/div if the calibator is accurate. You could check it with a counter if you can borrow one.
The timebase on the calibrator says ~1KHz, so it's probably not crystal controlled. My counter says mine is running at 986.37 Hz.
Household power is a pretty good reference at 60 Hz. Use a transformer.
If you have an old digital watch, it'll contain a 32768 Hz crystal-controlled timebase that is accurate to 50 parts per million or better, usually considerably better.
Reply to
Don Foreman
Do me one favour: Please don't connect your scope to the mains or then genset. It might kill you, judging from the questions you ask here.
~ This means "about". And you will get only about. Noone cares about the frequency. The rect-wave is for calibrating the Vpp and the compensation of the probe. Nothing more.
Thanks, Nick
Reply to
Nick Müller
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Reply to
Dave
The calibration bar is to calibrate the 10X scope probes. There is a capacitor on the probe that gives you an adjustment to get a near perfect square wave. The voltage should be very close but the frequency is rarely exact. The capacitor probably will have little effect at 1X. Glenn
Reply to
Glenn
The var knob should be turned full clockwise for the vertical scale to be correct. Tektronic scopes have a detent when the var is turned full clockwise. It seems to be correct from the numbers you gave. If you assume that the calibration voltage is right, 300 mv., and your sensitivity is set for 50 mv per division, 300 mv will deflect the display six divisions.
John
Reply to
John
I've no clue about the correct answer but you might want to download the PDF file found here and look it over:
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which is a primer on scopes by Tektronix. Here's another on probes:
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Mike
Reply to
Mike Henry
Thanks Glen. That makes perfect sense. The probe came with instructions to clip it to the bar and adjust the probe with a plastic screwdriver that came with the probe. Eric
Reply to
Eric R Snow
>Eric R Snow wrote: > >> The display shows the square wave with 6 divisions vertical and just over >> 10 divisions horizontal. Using the VAR knob in the center of the time/div >> knob I can adjust the display to show exactly 10 divisions. When this is >> done is the display correct? Or is it the calibration bar that is wrong? > >Do me one favour: >Please don't connect your scope to the mains or then genset. It might >kill you, judging from the questions you ask here. > >> This bar is labeled as 300 mV 30mA ~1KHz. > ~ >This means "about". And you will get only about. Noone cares about the >frequency. The rect-wave is for calibrating the Vpp and the compensation >of the probe. Nothing more. > > >Thanks, >Nick >-- >Motor Modelle // Engine Models >
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-> YADRO
Reply to
Eric R Snow
First: Because probes normaly only have an isolation voltage of 400V. I already hear your answer. But it is wrong.
Second: You have to connect the probes GND somewhere. And this is where your problems start.
Your question is OT here. It doesn't matter that much, because there is more OT than OT (on-topic) here. But in your case, it matters. You might get stupid answers. So please ask in an electronics group. They will tell you solutions that are quite save.
BTW: Don Foreman gave you a save answer.
Nick
Reply to
Nick Müller
For accurate calibration of the hor. sweep, you need either a frequency counter or calibrated [crystal controlled] signal generator to sync the signals with. A dual trace scope is handy for this. Bugs
Reply to
Bugs
I know Nick. I saved it. Thanks, Eric
Reply to
Eric R Snow
From reading the original post, it sounds like the time-base is spot-on, and the cal. oscillator is a little under 1 KHz. 10 X .1 ms = 1 ms, and 1/1ms = 1Khz.
Cheers! Rich
Reply to
Rich Grise
I don't know what the "calibration bar" is, but if you're talking about that little loop, the frequency isn't guaranteed to be accurate: in '~1000Hz', the '~' means "approximately".
If the scope is in cal, then the sweep is calibrated when the var. knob is turned all of the way clockwise, until the detent clicks.
What it's showing you is that your internal calibrator isn't calibrated for frequency, which it says right on the front panel: " ~1000Hz ", so it's not "wrong", either.
Hope This Helps! Rich
Reply to
Rich Grise

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