Using Limit Switches

[ASU]

Forum,

I'm learning more and more about the us of DAQ cards and my questions today is. How would I connect a limit switch to a DAQ device in order to communicate a stop or start?

I have a SPDT switch (OMRON D2MQ series switch). I'm using a DAQ card vs a motion controller because we have an abundance of them and dont want to buy an additional card.

dc

[DR_redviking]

What type of DAQ card is it?  I think on M Series cards, you can use a Change Detection event with digital inputs to trigger an event in an Event Structure.  Then you should be able to send a start or stop message within you application.  There should be an example of how to do this in the LabVIEW examples or somewhere on the NI site.

[Brooks_C]

Hello ASU,

Hurricane82d is correct; you can use a change detection event on a digital line to monitor your limit switch.  There is an example available in the LabVIEW Example Finder.  (Open LabVIEW and go to Help» Find Examples... Navigate to Hardware Input and Output» DAQmx» Digital Measurements» Read Dig Chan-Change Detection.vi.  This will allow you to trigger a software event.

There are other possibilities you using the digital trigger to control your DAQ card.  For instance you can use it as a start trigger to start a task, a reference trigger to take samples, or you could even gate a counter task and control a sample input or output clock with the trigger.  Unfortunately you cannon use it as a start/stop trigger directly.  The closest you can get is gating a counter task.  If the default stat of your limit switch is gnd then you can gate a counter output task that you use to generate a clock when the gate goes high.  You can choose how you want to use this signal depending on what you want to have happen when this limit is reached.

If you'd like to post more information about your application, setup, and goals it would be easier to make recommendations.

Cheers,