Simultaneous (Multiple Channel) Data Logging with M-Series (NI 6221)

[ChrisFTC]

Hi,

I was wondering, if it is possible to use a M-Series Card (NI 6221) to log multiple analog input channels simultaneously.

Regards,

Chris

[SG_ENGINEER]

Hi

you certainly can do that. since there are 16 analog input you can log up to 16 analog outputs simultaneously. use the DAQ assistant to select the channels that you want and you are on your way!

Goy

[ChrisFTC]

Sorry, Im confused. You are saying that I can do the same thing with an NI 6221 as with an NI 7831R, which apparently has dedicated ADCs per channel and explicitely allows simultaneous logging on all 8 channels? I thought the NI 6221 has all input channels muxed to one ADC.

Christoph

[Dennis_Knutson]

You can acquire and log 16 different channels but the acquisition is not "simultaneous". As you apparently know already, the card has a single A/D, so the difference between acquisitions is the inter-channel delay. You question referenced logging which is different than acquisition and the logging of 1 or more channels is done with a single function.

[ChrisFTC]

Hi Dennis,

Thanks for your answer. I have just one more question: does the 6221 have a SSH (simultaneous sample and hold) architecture or just the "simple" signal-mux-adc configuration? I couldnt find anything about that in the datasheets.

Thanks,

Christoph

[Dennis_Knutson]

I believe it's just the mux with single A/D.

[AlanArmstead]

.....That's correct.  The NI 6221 does not have any sample and hold circuitry.  So you can not get truly simultaneous measurements.  However, you can set the interchannel delay of the acquisition.  In NI-DAQmx, it is the convert clock that controls the rate in which the separate channels are scanned.  This rate can be queried or set with a DAQmx Timing property node (Property is: More>>AI Convert>>Rate).

-Alan A.

[ChrisFTC]

Thanks for the information.

Unfortunately, I dont have DAQmx installed right now, but would you know what the smallest amount of delay between two readings on two different channels is (e.g. ch1/read - delay - ch2/read)? Thanks.

Christoph

[AlanArmstead]

The max convert clock rate is the same as the max sample rate of the board.  So the max convert clock rate for the PCI-6221 is 250kS/s.  This means that the smallest interchannel delay you could have would be 4 micro seconds.  Hope this helps!
-Alan A.

[ChrisFTC]

That actually helps a lot. Thanks.

So, if I sample 16 channels one after another that leaves me with 64us (16*4us) of delay between the first reading of channel 1 and the second reading of channel 1 right? And if my requirement is to sample data every 100us that should be possible even with the NI 6221 (compared to the NI 7831R with fully simultaneous setup).

Sorry, I am just getting started with all of this stuff and I am a tiny bit confused about whats possible and whats not. 🙂 I really appreciate your help.

Chris