AC signal measurement with DC offset

[NAUSHICA]

I have PXI-6289 DAQ card & I want to measure an AC signal with DC coupling. peak to peak of the signal is abt 0.5V but has a DC offset of 2.5V.
of course I can measure the signal with +-5V range. But is there anyway to cut this DC offset & measure the AC signal only?
I want to maximize resolution of AC signal.

Regards.

Naushica

[devchander]

This card has only with DC coupling.

It does not have AC coupling (which would have removed the DC offset)

[NAUSHICA]

Well if it cannot be done with the PXI-6289,
Is there any option modules (like SCXI-xxxx) so I can perform this job?

If I can find an HPF which the cut off freq. lies below 10Hz may do  the job same isn't it?

Rg

naushica

[devchander]

Yes, using a SCXI 1125( or equivalent) with with a SCXI 1304/1305 terminal block will give AC coupling potential to your DAQ card

[NAUSHICA]

Thanks Dev,
I went through the SCXI-1125 manual again & in the appendix B, it is mentioned abt TBX-1329 which you can work with both AC & DC coupling.

my question is that, TBX-1329 has 250Vrms working voltage. Does that mean I can use this to measure pure AC signals of abt 100V and also with
small DC coupled AC signals?

Regards.

Naushad

[E Murphy]

Hi Naushica:

Try a 0.47 microfarad capacitor in series with your signal and a 100k ohm resistor from the input (the other side of the cap) to ground. This filter will block any DC and the corner frequency is about 3.4 Hz.

Regards

Eduardo Murphy

[JasonJiang2006]

Hi, I use PCI6251 and BNC2110 connector. I input a AC signal with some DC offset. I use a 10nF to block the DC offset, it works when I connect the offset signal to scope, the DC offset is blocked. However when I use the same way to the PCI6251+BNC2110, there always a DC offset signal shown in Labview, which is the same as the original offset. I don't know why it doesnot work this time.

Thanks

[YatinM]

hi jason

there are a couple of things you can try, firstly on your bnc-2110 block there are switches that determine the mode that the signal is aquired, either floating or ground, try switching between the two and see if that makes a difference. ideally on the PCI 6251 the mode that you need to make sure it is in is differential.
what is the DC offset that is seen in labview?

let me know how you get on and if you have anymore questions

YatinM
NIUK

[NAUSHICA]

I have an SCXI-1125 connected in parallel mode to PCI-6289.
Devices are connected through SCXI-1349 breakup module with an SHC-68EM cable.

If I want to implement a HPF circuit to cut frequuencies <1Hz,
Is it ok to implement the circuit at the output of SCXI-1125 and then feed it
SCXI-1349 to digitize with PCI-6289?

I want to measure a pure AC signal (10Hz) with max resolution and Signal may range from
few 10s of Volts to few milivolts. the DC offset is almost constant and is about few hundred milivolts.

Rg

Naushica