Author Topic: Agilent/HP 3312A Strange DC offset issue  (Read 3448 times)

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Offline opa627bm

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Agilent/HP 3312A Strange DC offset issue
« on: March 15, 2013, 04:36:44 pm »
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 ?
 

Offline AlfBaz

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #1 on: March 15, 2013, 04:53:04 pm »
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 3-2
Quote
5 OFFSET: R616 sets the dc operating point of any function. CAL position removes the dc offset. Eac +Edc must be less than 10V or clipping of the waveform will occur

To verify see if its clipping at 10V
 

Offline opa627bm

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #2 on: March 15, 2013, 05:07:01 pm »
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 3-2
Quote
5 OFFSET: R616 sets the dc operating point of any function. CAL position removes the dc offset. Eac +Edc must be less than 10V or clipping of the waveform will occur

To verify see if its clipping at 10V


Thanks for the response!, The clipping happens at all ranges, even I set the amplitude of the function to 1V-pp, the clipping still happen.
 

Offline opa627bm

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #3 on: March 15, 2013, 05:12:15 pm »
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...
 

Offline amspire

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #4 on: March 15, 2013, 05:15:03 pm »

Thanks for the response!, The clipping happens at all ranges, even I set the amplitude of the function to 1V-pp, the clipping still happen.
That 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.
« Last Edit: March 15, 2013, 05:19:59 pm by amspire »
 

Offline AlfBaz

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #5 on: March 15, 2013, 05:15:32 pm »
When you turn the knob to change the offset the sine wave flattens out. At what voltage is the flat spot?
 

Offline opa627bm

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #6 on: March 15, 2013, 05:27:52 pm »
When you turn the knob to change the offset the sine wave flattens out. At what voltage is the flat spot?

at negative rail it is -15.4V
 

Offline opa627bm

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #7 on: March 15, 2013, 05:28:25 pm »
When you turn the knob to change the offset the sine wave flattens out. At what voltage is the flat spot?

Positive rail is 14.4v
 

Offline opa627bm

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #8 on: March 15, 2013, 05:38:41 pm »
I have tracked the signal into the output amplifier and the signal amplitude is 1v p-p
 

Offline amspire

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #9 on: March 15, 2013, 05:42:28 pm »
I have tracked the signal into the output amplifier and the signal amplitude is 1v p-p
You 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.
 

Offline opa627bm

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #10 on: March 15, 2013, 05:50:16 pm »
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.
 

Offline amspire

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #11 on: March 15, 2013, 06:01:26 pm »
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.
If 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.
 

Offline opa627bm

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Re: Agilent/HP 3312A Strange DC offset issue
« Reply #12 on: March 15, 2013, 06:20:27 pm »
I can change the vernier setting and be able to move the offset at all level without clipping.....
 


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