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TA132 noise rejection mismatch

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TA132 noise rejection mismatch

Postby rodalsa » Sat Jul 11, 2015 1:42 pm

I just received a 2207A. While putting the scope through my new device tests I discovered that the TA132 probes that came with the unit did not have the same ambient 60 hz noise rejection under a specific test condition. Here is the test setup.

1) USB connection to my Dell Optiplex 990
2) Operating system: Windows 7 Professional
3) Scope software: PicoScope 6
4) Probes: TA132. As provided with the scope.

The probes are connected to the scope.
The AWG input is open. No BNC device connected to the scope.
Both probes are set to 10:1 and shorted using their associated grounding clips.
The grounding clip wire is arranged to have minimum area between them.
Both probes are laying side by side with their cables having minimum area between them.

The consequence of visualizing the signals from Channels A and B are shown in the attachment TA137 Probe Test 01.dc.

The activity that reveals the mismatch in noise rejection is simple. I touch the terminator box on each probe by lightly placing my thumb on the printed top of the box and my forefinger on the bottom of the box.

Attachment TA137 Probe Test 02.dc shows the results of this test.

The original post that I was preparing had additional comments below this space. Somehow during the Preview activities they disappeared. I do not have the time to type them all back into this post so it ends here today.

For me to believe is insufficient for you to know. - rodalsa
Attachments
TA137 Probe Test 02.gif
TA137 Probe Test 01.gif
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Re: TA132 noise rejection mismatch

Postby rodalsa » Fri Jul 17, 2015 12:30 pm

I've found the time and the memory that should fill in the missing part of my original submission. Sorry about the delay.

The top (first) graphic shows the two probes output while my fingers were on the probe terminator box of the affected probe. The bottom (second) graphic shows the two probes output while my fingers were on the non-affected terminator box. Walla! That should not happen!

I want to know what I need to do to get two probes that operate identically (well a lot closer to identical than these two probes). It seems ridiculous to return the entire purchased product to the seller especially since the seller does not have the facility to test two probes as I have done to make sure they do not suffer from the problem. Nor do they have the expertise to correct my interpretation concerning which probe is the bad one. Of course to claim that the probe that was not affected with the doubled to tripled increase in 60 hz amplitude is the "bad" one is possible though unlikely.

Another issue has surfaced. In the intervening time I received an email from technical support regarding a Ticket Number: TS00070226 that I was supposed to have submitted. Does anyone out there know anything that would tie that ticket number to this issue?

I responded to the email several days ago and have not received any responses as of this time.

Thanks for your help on both issues.

Rod
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Re: TA132 noise rejection mismatch

Postby rodalsa » Sun Jul 26, 2015 12:58 pm

It appears that I have posted my topic in an inappropriate forum.

Any suggestions re a more appropriate forum?

Rod
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Re: TA132 noise rejection mismatch

Postby Martyn » Tue Aug 04, 2015 6:50 am

Have you completed the frequency compensation adjustment procedure as detailed ?
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Re: TA132 noise rejection mismatch

Postby rodalsa » Tue Aug 04, 2015 2:01 pm

Not until you mentioned it. The probes both demonstrated critical dampening at 1 Khz.

The effects of the critical dampening of a 1 khz square wave signal referred to a 60 hz sinusoidal waveform was not expected to be significant. The frequency ratio is 16.67 to 1. The "rise time" of a 60 hz signal is well below the rise time of the 2207A scope.

I tested my expectations by selecting a 60 hz sinusoidal signal at 1 volt peak to peak then varying the compensation for the probe from full clockwise to full counterclockwise. There was no observable effect on the shape or amplitude of the waveform.

I currently am working with the vendor of the scope on this issue having referred them to this thread as a preparation step in the issuance of an RMA.

For me to believe is insufficient for you to know. -- rodalsa
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