Acquiring two input signals simultaneously

Hi,
I have an LVDT and a force sensor (both attached to a motor) plugged into my SC board and I am trying to read out & save the output data from both sensors simultaneously while the motor is in motion. The SC-2350 board is connected to the laptop via DAQCard 6036E . Two questions:
1) in my block diagram, the DAQ assistant blocks for both sensors are wired to their respective waveform graphs (one for the LVDT signal and one for the force signal), the whole being included in a while loop (which remains true until the motor stops moving). When running the program, only one signal is read out at a time and I have no control on which signal is transmitted (this seems to occur in a random fashion). Do I need to "link"/synchronize the two DAQ assistants in some ways so that both signals will appear simultaneously? If so, how would it be possible?
2) ideally, I'd like to read out both input signals on the same graph (with 2 different y-scales but the same time scale) to observe the phase shift. I tried to "bundle" the two data output coming from the two DAQ assistants but it resulted in an error saying that the two outputs were of different types. Is there a way to plot these two physical quantities on the same graph even though they're different and come from different sensors?
Thanks for your help!
Thibault.

Hello Dani,
I assume, based on your position sensors and the image you posted, that you are using counters to acquire your data. Is this correct? If so, it is important to note that you cannot add multiple counter operations to a single task because they have different timing requirements and all channels in a single task must share the same timing and triggering. In fact, if you attempt to add a second counter channel to a DAQ Assistant for a counter operation, you will receive the following error when you try to close the configuration window:
So, you will have to use two different tasks to acquire your counter data. You can do this either by using two separate DAQ Assistants or by using two different tasks in the NI-DAQmx sub-VIs in LabVIEW. Since you are trying to compare the phase difference between the two measurements, you will also need to synchronize the operations so that you are reading from both counters simultaneously. There are several resources online which discuss synchronizing counters, and I have linked some that I thought might be useful below:
KnowledgeBase 1JPES6LL: How Do I Synchronize a Buffered Quadrature Encoder Measurement to a Signal
KnowledgeBase 3GGATSCC: Hardware Counter Start Trigger for Counter Synchronization
It would probably be easier to use the NI-DAQmx Sub-VIs to implement this synchronization because they give you more control over specific parameters of your task. You can use the NI Example Finder to browse some examples which use the NI-DAQmx sub-VIs for counters. You can open the NI Example Finder by going to Help>>Find Examples... in LabVIEW. Once in the NI Example Finder, you can find the counter examples by selecting the Browse tab and navigating to Hardware Input and Output>>DAQmx>>Counter Measurements; then you can select the Position category (shown below) to find the Position measurement examples.
Let us know if you have any other questions about taking position measurements.
Message Edited by Matt A on 04-09-2008 03:55 PM
Matt Anderson
Hardware Services Marketing Manager
National Instruments
Attachments:
Error -200147.jpg ‏32 KB
Example Finder Position.jpg ‏124 KB

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Hello @fbinim,
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Acquiring two input signals simultaneously

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