Questions about WLS 9215 and PCI 6601

[kid_26]

Hi all,

I have a project in which I need to measure force of a load cell as well as speed. The load cell is able to generate three kinds of force in three direction, x, y and z. I will be using WLS 9215 to measure these three forces and PCI 6601 to measure the speed of rotary encoder. This is my first time using LabVIEW to develop an application.

1) Can I combine these four measurements in one DAQmx task? Or do I need to create one task for the three forces and another task for the speed?

2) If two tasks are required, what is the most feasible way to do timestamp synchronization? This is in terms of the time when data is received by LabVIEW.

Thank you for the input.

Kind Regards

[Boon Chen]

Hi kid_26,

Since you are using 2 separate hardware, you should be using 2 separate tasks (one for the 3 forces and one for the speed like you mentioned).

These 2 pieces of hardware cannot be exactly synchronized (ie. sharing clocks and triggers) but if you need the time when LabVIEW receives the data, you can use a software function "Get Date/Time in seconds.vi".

Best Regards,

Boon Chen

[kid_26]

Hi Boon Chen,

Thanks for your reply. 

If I start the two tasks simultaneously, do you have any idea what the timestamp difference would be? 

I am looking at the maximum of 0.5 ms difference between these two tasks.

Regards,

kid_26

[Boon Chen]

Hi kid_26,

I'm afraid the timestamp difference will be system-dependent and it will not be a deterministic number unless you do some form of synchronization between the devices.

If you need the devices to be synchronized, you can make use of PFI0 on the WLS-9215 device to take in a starttrigger, and send the starttrigger out from the PCI-6601 board. This, however, will probably defeat the purpose of using a wifi-daq device in the first place since you have to connect a wire between your 2 devices.

Best Regards,

Boon Chen

[kid_26]

Hi Boon Chen,

I agree that with you that wiring the two devices will defeat the purpose of having the wifi-daq.

In this case, is there not any workaround for this? I am not looking at a fully synchronized system since I understand it's impossible, but a slight difference would be tolerable.

Thank you.

[Boon Chen]

Hi kid_26,

Without hardware synchronization, the best we can do is to make sure that the 2 data acquisition tasks are independent of each other, so the computer should run 2 tasks in parallel according to LabVIEW's dataflow.

We would not be able to guarentee that the time difference between the 2 tasks starting though. Even if you do get it below 0.5 ms once, it does not mean that if you re-run the program the same timing can be achieved. This is what I mean by indeterministic.

Have you tried out your program to see if the behavior is acceptable?

If you need further assistance, perhaps you can email your code to asean.support@ni.com and let us know more information about the application you are trying to build so we can see if there's any better recommendations.

Regards,

Boon Chen