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Thread: Problem with phase shifting 33120A and 33250A.


Permlink Replies: 4 - Pages: 1 - Last Post: Apr 21, 2011 6:31 PM Last Post By: lhornburg
vostok

Posts: 3
Registered: 04/15/11
Problem with phase shifting 33120A and 33250A.
Posted: Apr 15, 2011 7:41 AM
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Hello,

I have a setup with 33120A driving a vibrating specimen and 33250A controlling short light pulses (about 1/100th of the vibration period) illuminating the sample.

When I offset the illumination frequency at, say, 1 Hz I see the sample apparently oscillating at 1 Hz as expected (the true oscillation frequency is in the kilohertz scale). What I like to achieve is to set the drive and illumination pulse frequencies equal and control the phase difference of the signals in order to image the my sample at different phases of the oscillation period. I have got the two generators synchronized via the 10MHz clock cable.

When I manually adjust the phase of 33120A (the newer one doesn't have a manual menu option) I see the sample moving corresponding to to the phase I just adjusted.

My problem is that when sending PHAS 180.0 etc. commands to the generators (either one) via GPIB, I see no movement or change in position. A GPIB query "PHAS?" confirms that the generators received my commands.

What seems to be the problem here? Any ideas?

Lauri Kangas, Finland
lhornburg

Posts: 483
Registered: 01/15/10
Re: Problem with phase shifting 33120A and 33250A.
Posted: Apr 18, 2011 2:45 PM   in response to: vostok in response to: vostok
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Hi Lauri,


• You can adjust the 33250A phase from the front panel
• What are you referencing the generators against? What is the external signal you are using to reference 0 degrees?
• Are you getting errors on the 33120A?
o The PHAS command isn’t a valid command on the 33120A (it is on the 33210A and 33250A but not the 33120A). You Need to use PHAS:ADJ on the 33120A instead.
o The PHAS:ADJ command on the 33120A is in radians and can be between -2pi and +2pi. Sending 180 radians exceeds these values. To specify it in degrees you need to do PHAS:ADJ 180 DEG.
• If the unit is already at 180 degrees from configuring it manually, sending the command PHAS:ADJ (to the 33120A) or PHAS (on the 33250A) 180 will not result in any change. Use the command PHAS:REF before using the PHAS:ADJ or PHAS command to prevent this from happening.
vostok

Posts: 3
Registered: 04/15/11
Re: Problem with phase shifting 33120A and 33250A.
Posted: Apr 20, 2011 3:17 AM   in response to: vostok in response to: vostok
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Hi and thanks for the reply. I think this explains my problems. I did have some confusion regarding the PHAS vs. PHAS:ADJ commands a while ago. I will try if I'll succeed with the correct commands.

Two more questions:

Where in the front panel of 33250A can I manually adjust the phase?

What kind of external reference would I need to achieve an accurate phase shift between the two generators besides linking them together with the 10MHz clock?

Lauri
vostok

Posts: 3
Registered: 04/15/11
Re: Problem with phase shifting 33120A and 33250A.
Posted: Apr 21, 2011 3:34 AM   in response to: vostok in response to: vostok
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Problem solved.

I could not find the phase menu in the 33250A front panel because of it's lacking when the output is set to Pulse mode. I reckon this the phase in this mode isn't controllable even via the remote interface?

However I changed my commands to PHAS:ADJ instead and send them to my 33120A controlling the sine output and now everything works fine!

Lauri
lhornburg

Posts: 483
Registered: 01/15/10
Re: Problem with phase shifting 33120A and 33250A.
Posted: Apr 21, 2011 6:31 PM   in response to: vostok in response to: vostok
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If you turn on Burst, you can adjust the phase of a squarewave, but not a pulse. Sorry for any confusion but I'm glad to hear you got things working.

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