Hello everyone, I now have a simple task that is feeding a voltage signal(from PXI ao0) to a circuit and then feedback a voltage across a component, for example say one of the resistors in the circuit, through ai0 on the PXI. So in this case, synchronization between analogue input and analog output need to be performed to avoid any phase shift error. I tried to build my VI by learning this example: https://decibel.ni.com/content/docs/DOC-3882 However I have a few questions. 1. I noticed that there is a merged error fed to the "start task"sub VI for analog output. What is the point of merging error? 2. I have attached my VI (also as shown below) for voltage output. I put my DAQmx write subVI in the while loop so that I can change the voltage while the VI is running.However, in the example, the author put the read outside the loop, and even before the start task. What difference will it make? 3. I also attached my synchronized VI. I still put the wavegeneration and DAQmxwrite in the loop. An error keeps popping out saying about samples being unavailable and it needs a higher sampling rate or longer waiting time. What causes this? I would appreciate if these problems can be sorted out. Thank you everyone.

pokenan a écrit :Hello everyone, 2. I have attached my VI (also as shown below) for voltage output. I put my DAQmx write subVI in the while loop so that I can change the voltage while the VI is running.However, in the example, the author put the read write outside the loop, and even before the start task. What difference will it make? As Alexander said, the Write.vi writes the data to the internal buffer. In countinuous output mode the output will always regenerate the buffered data. If you put the Write.vi inside the while loop you should put a write node (before the StartTask vi) and set the Regeneration Mode property to Do Not Allow Regeneration to avoid glitching. Also use a Channel node to set the Data Transfer Rate Condition (probably to Onboard Memory Empty in your case but you will have to try the different values). Have a look at this document on the subject. You should also put a Write.vi before the loop to make sure data is available for the Read.vi in the first loop iteration. I would also try adding a DAQmx Is Task Done.vi after the Write.vi inside the loop. Ben64

1) First you need to start acquisition task, it will wait for trigger to arrive. Then you start generation task that provides this trigger. Otherwise acquisition might skip trigger and never start.3) First you need to write something into buffer (DAQmx write), only then you can generate it (Daqmx Start). Check Cont Gen Voltage Wfm-Int Clk-Non Regeneration.vi in Help -> examples for example.

LabVIEW

Questions on synchronization between analog input and output

Solved!

Another "gotcha" that you should watch to avoid is the sample rate is not always what we specify. DAQmx will find a rate as close to the desired as it can support. The output of the Timing DAQmx function will return the actual sample rate.

Ben

Retired Senior Automation Systems Architect with Data Science Automation LabVIEW Champion Knight of NI and Prepper LinkedIn Profile YouTube Channel