DAQ Read VI reading reading random Value

[IamAbhishek]

I am Ploting sine wave on CRO using C DAQ 9135 controller and reading the same sine wave on CRO by shorting the input and output terminal on hardware side.
Until this everything is fine. But when I am reading the same value(output waveform through shorting on hardware side as input to DAQ) on waveform chart point by point .
DAQ intially 30 to 50 points read some random value.

CRO side everything i am getting is fine.

I have attached

1. VI
2.Waveform Chart Image
3.CRO Image

[RavensFan]

The output execution path is running parallel to the input execution path.  There is nothing that synchronizes the two.  Probably the DAQ Read is occurring before the DAQ write has a chance to start, so you are reading some random noise on the input line.

Direct your error flow wires so that you guarantee the DAQ Write occurs before the DAQ Read

[IamAbhishek]

I have tried readng after writing but still it is not working.

[dsb@NI]

Try running a continuous acquisition, start it before running your finite generation to capture the signal before the output even starts. See if you observe unexpected signal. 

If you really want to align a generation with an acquisition, you should make sure to synchronize the start, and also be aware that some devices have delay. For instance, the 9234 specs the following:

>Input delay (40 + 5/512)/fs + 2.6 μs

Which devices are you using? What is the delay for those devices?

Also, while your CRO signal looks clean, the cDAQ image looks like it has significant noise. Were these images taken for the same data set? Could there be a cabling or grounding issue that is compounding the noise observed?

I suggest starting with the DAQmx examples. Run ao and ai examples simultaneously. Do you see the same behavior?