Vi for an optical cable encoder?

Question

Hi im am fairly new to DAQ on labview and i have an optical encoder which pulses every 0.5 degree (so 720 pulses in one rev), it is attached to a scb68 connector block which is attached to a PCI 6111S card via a cable.
Is there a specfic example that i could look at to get the hang of things? i want the counter for the pusles to reset itself after every whole revolution. any suggesstions would be most grateful.
Thanks
Notay

Answer 1

The examples that ship with LV illustrate how to use the counters.
In terms of the reset, do you want to reset every 720 pulses, or once a rotation - the two are subtly different. You can take the count out from the counter and do a MOD 720 function and use the remainder output. This will give an output that restarts every 720 pulses. The one potential problem is that the reset point will not be in the same place relative to the shaft position from one run to the next - but this might not be an issue.
The other way to do the reset is to use an encoder that has two outputs, one (as in your case) every 1/2 degree of rotation; and one every 360 degrees of rotation. You can then use that once-per-revolution output to reset the counter in hardware. Plus, you can align that mark to some known position like TDC (top dead-center) so the counter output can tell you the shaft's absolute rotational position.
One thing to be on the look out for is that the counter inputs can be very particular about the input waveform. Make sure the signal at the computer is a nice, neat square wave. No undershoot, no overshoot, and no ringing.
Mike...
Message Edited by mikeporter on 07-24-2007 05:50 PM
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