Agilent/HP 3312A Strange DC offset issue - Page 1
Forum section: electronics / testgear

author: opa627bm
author_rank: Regular Contributor
timestamp: March 15, 2013, 05:36:44 am
content: Hello, I got this 3312A from ebay and I test all the function except the DC offset part, it have a strange clipping problem when I change the DC offset knob. Anyone have any suggestions about how to fixing it ?

author: AlfBaz
author_rank: Super Contributor
timestamp: March 15, 2013, 05:53:04 am
content: Seems to me that if you are going to change the offset of a waveform eventually the peak of the waveform will reach the supply rail and clip.The manual says on pg 3-2QuoteTo verify see if its clipping at 10V

author: opa627bm
author_rank: Regular Contributor
timestamp: March 15, 2013, 06:07:01 am
content: Quote from: AlfBaz on March 15, 2013, 05:53:04 amThanks for the response!, The clipping happens at all ranges, even I set the amplitude of the function to 1V-pp, the clipping still happen.

author: opa627bm
author_rank: Regular Contributor
timestamp: March 15, 2013, 06:12:15 am
content: I have traced to TP9, the waveform will shift slightly as I turn the offset knob but no clipping occurs. I can't find to10...

author: amspire
author_rank: Super Contributor
timestamp: March 15, 2013, 06:15:03 am
content: Quote from: opa627bm on March 15, 2013, 06:07:01 amThat can happen if the range attenuation is after the output amplifier. Most of these generators have the attenuation after the output amplifier so that you do not get the output amplifier's base noise level intruding at very low amplitude outputs. If it is clipping at +/- 10V on the maximum amplitude range, then almost certainly you are just reaching the generators limits.

author: AlfBaz
author_rank: Super Contributor
timestamp: March 15, 2013, 06:15:32 am
content: When you turn the knob to change the offset the sine wave flattens out. At what voltage is the flat spot?

author: opa627bm
author_rank: Regular Contributor
timestamp: March 15, 2013, 06:27:52 am
content: Quote from: AlfBaz on March 15, 2013, 06:15:32 amat negative rail it is -15.4V

author: opa627bm
author_rank: Regular Contributor
timestamp: March 15, 2013, 06:28:25 am
content: Quote from: AlfBaz on March 15, 2013, 06:15:32 amPositive rail is 14.4v

author: opa627bm
author_rank: Regular Contributor
timestamp: March 15, 2013, 06:38:41 am
content: I have tracked the signal into the output amplifier and the signal amplitude is 1v p-p

author: amspire
author_rank: Super Contributor
timestamp: March 15, 2013, 06:42:28 am
content: Quote from: opa627bm on March 15, 2013, 06:38:41 amYou cannot have over 10vp-p on the output and 1vp-p on the amplifier output. Are you talking about the amplifier input?Anyway that looks like it exceeds the specs.

author: opa627bm
author_rank: Regular Contributor
timestamp: March 15, 2013, 06:50:16 am
content: Sorry about my confusing language, what I meant was the input signal is 1v p-p at the input test point of the output amplifier.

author: amspire
author_rank: Super Contributor
timestamp: March 15, 2013, 07:01:26 am
content: Quote from: opa627bm on March 15, 2013, 06:50:16 amIf you lower the AC with the vernier instead of the range switch, can you get a large DC offset relative to the AC level - in other words on a particular output amplitude range, is the DC offset setting separate from the amplifier amplitude control knob? If it is, I think you will have no trouble generating, say, a 5vpvp squarewave going from 0v to5v.If you want 1uV sinewave output on a 10Vdc signal, you just use an external 10V DC source and 50 ohm resistor in series and connect the generator via a capacitor between ground and the 50 ohm resistor.

author: opa627bm
author_rank: Regular Contributor
timestamp: March 15, 2013, 07:20:27 am
content: I can change the vernier setting and be able to move the offset at all level without clipping.....