Author Topic: Tektronix 561A Calibration  (Read 1433 times)

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Online Cyberdragon

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Tektronix 561A Calibration
« on: October 26, 2016, 11:39:36 pm »
Starting of with a rant :rant: on a specific issue, although I'll post anything else on the calibration of this unit here too.

I have the base unit working mostly within spec (except I have not checked the HV level or a few of the secondary voltages) but that was pretty easy becuase the manual was of the quality you would expect from Tektronix. :-+

The 3A1 plugin manual however... >:( :palm: (Can't post it here, I don't remember the link, but you should be able to find it.) The problem I notice is the input amplitude is a bit low. I don't have a standard, but I adjusted the calibrator so I used that (it doesn't have to be perfect). However...I can't calibrate it because the manual is wrong! The plugin is for the entire 560 series, so someone made a mistake in considering all models. It asks to set the input to DC .01V and adjust the level to 6 large divisions with 50mV (it says to go back to 5 later). But the 561A only has FOUR divisions on each side of center! >:( They even show a 561A in the diagram! :palm: I would just set it to AC and set it to 2.5 divisions each side, but the square wave is not straight in AC mode (another problem). Yes, I am using 50 \$\Omega\$ cable, it's already been upgraded to BNC jacks, so it is an input problem. And there is only one set of instructions, not different ones for each model. :--

So now what? How do I adjust the input amplitude? Can I use a different voltage and still get correct calibration?

EDIT: :o that omega symbol is also wrong by a few divisions... :-DD
« Last Edit: October 26, 2016, 11:44:07 pm by Cyberdragon »
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Offline andy2000

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Re: Tektronix 561A Calibration
« Reply #1 on: October 27, 2016, 05:46:13 am »
You could start with the trace 2 divisions below the center line.
 

Online Cyberdragon

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Re: Tektronix 561A Calibration
« Reply #2 on: October 27, 2016, 05:43:58 pm »
You could start with the trace 2 divisions below the center line.

I'll try, but it seems to be clipping the signal (reducing higher voltages more than lower ones). Hopefully it can be adjusted correctly.
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Offline David Hess

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Re: Tektronix 561A Calibration
« Reply #3 on: October 29, 2016, 07:28:26 am »
It is normal for there to be some non-linearity so accuracy is only specified over the center divisions but if the non-linearity is too great, then that indicates a problem.  The linearity is tested by displaying a 1 division signal at the center of the CRT and then watching to see how it changes with vertical position.

It asks to set the input to DC .01V and adjust the level to 6 large divisions with 50mV (it says to go back to 5 later). But the 561A only has FOUR divisions on each side of center! >:( They even show a 561A in the diagram!

Just use a 40 millivolt peak-to-peak signal at 0.01V/div for calibration.  There is nothing sacred about 60 millivolts.

There may have been an mid life change to the CRT for the 561A which altered the number of vertical divisions.
 


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