Logic Level Limit Switches and Mesa 7i77

I'm working out the schematic for my Hurco SM1 conversion, and I've noticed what appears to be a problem. It looks to me like inputs all need to apply field voltage to the input pin to be detected ( or 60% of field voltage at a minimum). My limit switches are inductive 5V limit switches. Can these be used with the 7i77 I've already bought? On top of that, I believe that my limit switches show 0V when activated. That's if I'm reading this diagram properly.

Do you have the PN of the limit switches? (They look like OPTO detectors in the picture)
They may well have a larger than 5V switching capability

But... they are wired rather strangely, especially if "COM SERVO" is ground
with the -OT switches wired in sourcing mode and +OT switches wired in sinking mode

If "COM SERVO" is ground, +OT SERVO will pull a positive voltage toward ground
and -OT SERVO will pull a negative voltage toward ground, almost like this was wired
into some analog +-10V cicuitry

It is actually wired in an analog servo system. OT servo channels return to the drive and disable the direction of travel they are wired to (- disables neg travel +disables positive travel). Com is in fact ground. OT software goes to the control board to inform the control of the limit. I believe that wierd switch is actually an optoisolator on the limit switch board, which is separate of the proximity switches. I will get the pn off the switches a little later when I can get back or to the mill. Thanks

I just found some more info, OT Software ± are actually the logic level INPUTS (0 or 5v) from the limit switches, AND signal to the current control board to signal limit reached. So, the way I believe it works is that when the limit switch is tripped, OT Software goes [strike]HIGH,[/strike] to ground (NPN SINKING SWITCH) turning[strike] off [/strike] on the LED in the optoisolator. This causes the optoisolator to turn [strike]off,[/strike]on, causing OT Servo to [strike]float(?)[/strike]go towards ground(?) So... OT servo + would show [strike]+OT voltage (I think 15v...)[/strike] ground when against a limit, and -OT Servo would [strike]show -15v(?)[/strike] show ground when against the neg limit(?)

So that part number for the switch is 101xk5-1. It's a normally open, NPN 4.5-5.5v inductive switch.

so if the Open collector outputs wont tolerate 24V
( hard to tell from what limited information is available on those prox's ),
there are a couple of options:

1. Use spare encoder inputs in TTL mode, these give you 5V inputs readable on the encoder A,B, and Index hal pins
So 2 spare encoders would give you your 6 inputs

2. Add a sserial TTL level input device (a 7I69 will give you 48 TTL level I/O pins. a 7I90HD, 72)

3. Set the I/O voltage of the 7I77 to 5V (this means you lose the 24V output capability )