Electronics > Metrology

Is it acceptable to calibrate my oscilloscopes with just a x-tal?

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BlownUpCapacitor:
Hi, the main purpose of this post is to settle a disagreement between my friend and I. When my friend saw how I calibrated my own oscilloscopes, he went on a rant saying how I shouldn't be using what I am using to calibrate my scopes.

For context, I am using essentially just a x-tal to calibrate my scopes. More specifically, a Global Specialties 4010 10MHz Crystal Controlled Pulse Generator. This is what I consider to be my lab frequency standard for calibrating all sorts of things, mainly oscilloscopes. This is only for the calibration of horizontal timing.

I don't calibrate modern DSOs, but rather old-school scopes such as the Tek 7904, Tek 2230, Tek SC502, 5110, 7613... etc.

Anyways, back to the point. You see, my friend insists that I use very accurate frequency standards like rubidium frequency standards. I personally think this is overkill, and just a simple X-tal controlled pulse generator is good enough.

What are your guys' thoughts?

bdunham7:
It should be obvious to anyone that can read and understand the scopes manual and specs that even a generic AWG will be sufficient for almost all CRO calibration.  Some higher performance versions could also use a fast-edge pulser of some sort and an accurate RF generator.  The specs for sweep rate and linearity are 1% at best in most cases.  I was able to do the calibration procedure on my 2465B with just what I've listed plus normal bench stuff and there's no faking it in that case since the scope either accepts or rejects your inputs.

TimFox:
I have a military-version Ballantine 6130A "time-mark generator" which is a good crystal oscillator and a switch-selectable frequency divider to get time marks in a 1-2-5 sequence over a typical analog CRO range of time-base settings.
Since one can resolve roughly 1% of the total time base (10 divisions, seeing 1/10 of a division) when comparing the pulse train to the total sweep, this is plenty adequate to calibrate an analog CRO.
The 22-position rotary switch allows checking the time base over a wide range of time/div.
Better oscillators, such as GPSDO or fancy Rb standards can be useful to calibrate a frequency counter, which has far better resolution (better than 1 in 106).
I learned about significant figures in 11th-grade chemistry class back in high school.

Whales:
The V and H gains on my CRO drift as it heats up, far more than the ppm of a standard quartz crystal.  Tweaking them to a rubidium standard would keep them within that level of cal for a few... seconds?  minutes?  I'd have to ovenise my CRO.

langwadt:

--- Quote from: Whales on March 01, 2024, 12:34:05 am ---The V and H gains on my CRO drift as it heats up, far more than the ppm of a standard quartz crystal.  Tweaking them to a rubidium standard would keep them within that level of cal for a few... seconds?  minutes?  I'd have to ovenise my CRO.

--- End quote ---

and how could you possibly see the difference on the screen?

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