Test for transmission speed (and frequency) when directly connecting output pin to input pin with AC square wave signals on USB NI 6289 DAQ

[stealthsniper]

Hello. I am trying to come out with a test to measure the highest square wave AC frequency that can output from the DAQ's output port and directly connect back to the DAQ's input port. I am investigating the effect of the sampling delay of the input port to make sure that the voltage sampled at the input port is same as the voltage generated at high frequency at the output port of the DAQ. So, what I am doing is comparing voltages, as well as determining the delay of sampling time at high frequency if the voltages are mismatch. Then determine at which frequency this mismatch occured.

May I know if there's a technique to do such a test? Preferable in python, but lets start with concepts first. Also, I dont think the DAQ's specification sheet shows the details on this. 

[Henrik_Volkers]

The 6289 uses multiplexed input chanels, so in addition to the cable length, i assume you will get delays depending on the number and read order of channels you read. AND have a look at the spec concerning source impedance and settle time and the input filter.  Sounds like you want to turn off all filters ... so have a look at mirror signals

Max frequncy output is half the output sample rate , and read it with the same SR (and to avaoid glitching you can change the active slope of one of them to better catch a peak. However the output, input and cable impedances will take effect.

if you start with moderate 'sine' frequencies  or equal sample square frequencies from 10k up to 250k  matching a rectangular FFT (the frequencies match the FFT bin)  and measure phase and magnitude (at the beginning also from the harmonics) you can measure the delays and transferfunction.