Analog Input Sampling Rate Question

[johnoc]

Hello, 

I have been working with NI equipment and software for a long time, but I have come across something I thought I understood but I am not sure at this moment. It pretty much pertains to any Multifuction DAQ card.

My example:

I have a PCIe-6353 1 MS/s aggregate when scanning multiple channels.

When measuring Single-Ended you divide the chosen sampling rate by the number of AI channels being scanned to calculate the sampling rate per channel.

What is the case with multiple differential channels? Since two AI channels are involved in the measurement of a differential channel. Is the sample rate per channel a function of the number of analog channels or the number of differntial channels?

[Kevin_Price]

In any of the standard MIO boards I've used over many years, single-ended vs. differential inputs do *NOT* change the aggregate sample rate possible.

Differential mode is implemented in the board's circuitry, it's *NOT* a net effect of the driver sampling ao0 and ao8 separately in single-ended mode and then taking a software difference.

-Kevin P

[johnoc]

So if you set up an analog input task and you set your sample rate to 100 kHz and have 16 channels being measured, All the channels in that task will be sampled at 100 kHz. Regardless of whether they are single-ended or differential.

[crossrulz]

1MHz aggregate sampling of 16 channels will actually give you a max sample rate of 1000kHz/16 channels = 62.5kHz

[Kevin_Price]

Correct for a faster board than yours at 100 kHz, correct for your 6353 (limited to 1 MHz aggregate) at, say, 10 kHz.  The designated channels in the channel list get sampled at the specified rate; there is no timing difference based on single-ended vs. differential configuration.

-Kevin P

[johnoc]

crossrulz

"1MHz aggregate sampling of 16 channels will actually give you a max sample rate of 1000kHz/16 channels = 62.5kHz"

This is what I was getting at when I said sample rate per channel. Does it matter if the 16 channels are Single-ended or differntial?

[crossrulz · Accepted solution]

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johnoc wrote:

This is what I was getting at when I said sample rate per channel. Does it matter if the 16 channels are Single-ended or differntial?

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No, it does not.  In the hardware, the ADC is differential, it is just a matter what gets connected to the negative side (AI GND for SE, AIX- for differential).

[johnoc]

Thank You!