Optical limit switch problem

[Telrad]

On my laser conversion, the home switches are optical. When triggered the switch outputs a 12v signal to the limit switch input on the DSP. When not activated I see a 1v signal to the limit switch input. The problem is when the laser head blocks the light the limit is not triggered, only when the light is unblocked and the voltage is 1 to the limit input the DSP throws up a limit trigger. Is there any way setting to change how the limit inputs are recognized? In mach I can set them to trigger high or low. Another idea would be to attach a solid state relay to each input to change the optical switch to a NO or NC switch.

Anybody deal with this issue before? I read in the forum where people have replaced the optical switch all together but I would like to keep mine.