One output and two input

[bsunny]

I am giving a ramp signal to a laser and taking the output from the photodiode.

When I use just one photodiode(one input), I get the proper results but when I try to take in two input from 2 separate photodiodes, it gives the error 

"waveform dt are different" . I am calculating on the fly average. I am giving same sampling rate and number of samples for all sample clocks. VIs has been attached.

[Dennis_Knutson]

Do not use two separate and sequential DAQmx Read tasks. Use a single task with both channels in the physical channel list and use NChan NSamp for the DAQmx Read.

[bsunny]

I tried that but then I cannot initialize the feedback using the waveform generation vi.