Sending request for negative dc voltage in hp 8904A

[ilyag]

Dear Sirs,

The hp 8904A instrement allows to apply negative DC voltage. However,in your driver to this instrument it doesnt succeed to apply negative voltage. I guess, I have to change the string "APA%.2eVL", right?

If yes,how to change it so that it would send negative voltage?

Thanks alot,

Ilya.

[Dennis_Knutson]

Since this board is for NI signal generators, you should have posted to the instrument control board. In any case, are you sure that's the correct function for setting DC? There is nothing wrong with the string syntax that would prevent a negative number being sent. I don't think I've used that particular model but for others, I've set the amplitude to 0 and applied a negative or positive offset. If you are getting an error back from the instrument, it's a pretty good sign that you are using the incorrect function. It's also a good idea to set it up manually and do a query of the instrument.

[ilyag]

Hi Dennis, Thank you very much for help. I dont get any error from instrument,it just sets DC amplitude zero for any negative number I send. The relevant part of the quary sended by this vi looks: "DEAOC1APA-1VL" All quaries like "DEAOC1APA1VL" do work,but for negative numbers it sets zero. Do you know how to fix this? Thanks alot, Ilya.

[Dennis_Knutson]

I've only taken a quick glance at the manual. Make sure that you first set the waveform type to dc.

[ilyag · Accepted solution]

well done! I also knew from the manual that negative amplitude is accepted only for DC option, but just didnt think about this.

Thank you very much! 

p.s. I suggest you to fix it in the drivers of your site - just to concatenate amplitude value after the waveform type and not before as it is now

[Dennis_Knutson]

Glad you found the problem. Since it's NI's site and not mine, I can't fix anything and since the driver is unsupported (originally from 1994), I doubt they would do it anyhow but you can never tell.

p.s. I think the idea is to mark the reply that solved the problem - not mark your own reply.

[ilyag]

Yes,I wanted to mark yours, I marked my reply by mistake.

sorry