6008 usb DAQ using Multiple analogue outputs at once reduces accuracy?

[Sam_R]

Hey guys,

I just wanted to know if anyone else had experienced a severe drop in accuracy when using both analogue ouputs at once on the ni 6008?

Also, the voltage seems to be half of what I've specified it to be

Thanks,

Sam

[ajmartin]

Well you may already know this but,  the analog out is limited to 150Hz. And I am not totally positive but I think if you use both channels that is cut in half.. On the voltage question, is it half even if you use one channel?  Can you post your code? I have a 6008 on my bench.

Alan

[ajmartin]

Hi Sam,

It was a little difficult for me to follow the block diagram you sent me so I can't really comment on that except there a LOT of express VIs. So I will just address the original question. That is does anybody experience a severe drop in accuracy when using both AO0 and AO1 at the same time. I played around with this for awhile since I do have a USB-6008. And since you are using Express VI's I used the Daq Assist for the Analog Output. The equipment I used to make the measurements were a Tek TDS 1002 Digital  Scope and a Fluke 111 Meter. I started just generating various voltage levels on each of the outputs both using single, then both channels. I  measured the results at the 6008 terminals with the fluke and they were spot on in both cases. Next I made a short piece of code that would generate random values to both channels at the same time and connected the scope to the output terminals of the 6008. As expected the frequency was erratic, but it was equally erratic whether using one or both outputs. I could slow the loop down enough to compare voltage measurement with the random numbers and they were still spot on. I did observe, at least in this test, that with both channels running the top frequency was around 65Hz and with only one channel it was close to 150Hz., So this was a long way around to answer your question, No I don't see any difference when running both analog out channels except the expected 150Hz limitation of the 6008

Alan

[ajmartin]

Here is the VI I used.

Alan