Giant 20' x 3' x 2' router build

[irving2008]

There are 6 in total 3 home 3 limit all pnp nc each one has a common + and - up to a junction box on the gantry were they go off on there own each have there own separate input wire on the csmio . the main wire is a 12 core cy screened and earthed at the control box all running on 24v

many thanks

So active low signal (i.e. break = limit/home hit), wired as per page 19 of the CSMIO/IP-M user manual?
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I have to say I doubt line capacitance is an issue at the CSMIO end. CY cable is 75-150pF/m so looking at 900 - 1800pF for 12m. So when switch opens that 1800pF has to discharge through opto-isolator/resistor. Assuming standard 10mA opto current, series resistor is 2200ohm, so fall time is approx 6uS worst case. One simple & quick test would be to put an additional 2200ohm 1/2W resistor to ground at the switch end of the cable (or even a couple in parallel). This will discharge the capacitance faster and will reduce the effective capacitive load on the switch. Try that first...