sample rate for USB 6215/versus channels

[pnielsen@gplains.com]

If I am using a DAQ 6215 in a differential mode with three inputs. 3 channels. How do I determin the sample rate versus accuracy?

[odessy27]

Umm.., The DAQ boards are usually calibrated and their accuracies are mentioned in the data sheet. I am not sure what you mean by accuracy vs sample rate. Is it accuracy as a function of sample rate?

[pnielsen@gplains.com]

The DAQ USB 6215 states 250K/s SI DM mode@16 bit. But I am trying read up to 8 differential signals. Does the sample rate of 250K stay constant for all channels or is it slowed down by the mux sample rate. I need a minmum of 16 bits to read. If I use one channel I get 16 bit accuracy in 1 Second. If I had 8 channels reading 16 bits what would be my accuracy and max sample rate be!

[crossrulz]

The DAQs do not have an accuracy vs sample rate.  They have an accuracy based on the range.  For instance, you USB-6215 will have an accuracy of 2.69mV at the -10V to +10V range while having an accuracy of 0.088mV at the -200mV to +200mV range.

[crossrulz]

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pnielsen@gplains.com wrote:

The DAQ USB 6215 states 250K/s SI DM mode@16 bit. But I am trying read up to 8 differential signals. Does the sample rate of 250K stay constant for all channels or is it slowed down by the mux sample rate. I need a minmum of 16 bits to read. If I use one channel I get 16 bit accuracy in 1 Second. If I had 8 channels reading 16 bits what would be my accuracy and max sample rate be!

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All of the channels will have the same 16-bit reading at a maximum of 250kS/s.  This unit does not have a S/s/channel like some older DAQ cards.

[odessy27]

From 6215 datasheet, it looks like 250k/s is the maximum data rate for the card. so depending on number of channels you use, your per channel maximum data rate will vary. If you use 8 differential, your per channel maximum data rate would be about 31k, if you choose 4 channels 62 k and so on. 

[Dennis_Knutson]

And the max sample rate per channel is the the max of 250 kS/s divided by the number of channels.

[pnielsen@gplains.com]

To all who have answered my question I thank you imensly. You have helped me greatly. Kudos belong to everyone.

[pnielsen@gplains.com]

All the replies are greate. Just one question. If I sampled the data at 10 times a second or 100 times a second with 3 differential channels would I still get 16 bit accuracy. Sorry for my confusion.

[odessy27]

 as crossrulz said, your 16 bit resolution is independent of the sampling rate. So, no matter how fast or slow you sample the data, you will always get 16 bit resolution for that card. The resolution in terms of voltage measurement will depend on the voltage range you select. 16 bit gives you 2^16 = 65536 steps. So if the range you select is 0 to 10V, 10/65536 = 150 microvolt will be your resolution.