First, verify that you indeed have +5V coming into the PMDX-108 on the ribbon cable from the SS. And make sure you have the PMDX-108's jumpers set as per "Example 2" or "Example 4" in figure 4 on page 8 of the PMDX-108 manual.
Currently I'm using J2 on the 108 board for my probe and it works perfectly. And J3 will be used for a pneumatic pressure sensor (24vdc).
Good. Now try moving the probe wire to J3, J4, J5, etc. and see if it works on each of them. You only need to move the wire connected to the "2" terminal, you can leave the wire on the J2 "<" terminal in place. This will show whether the inputs do function independently (as they are supposed to do).
There are 5 outputs from the spindle, each returning 24vdc when activated.
What do they output when NOT activated? Do they output 0V (i.e. they switch between 0V and 24V)? Or are they like PNP outputs (as PLC outputs often are), where they output 24V when "active" and high impedance when not active? Note that the PMDX-108-Input does not support PNP-style sensors (according to the web page
http://www.pmdx.com/pmdx-108-input).
The first way is to power it via a shared 24vdc power supply. 0vdc is connected to <J4 and J4 is the sensor wire from the spindle that carries the signal for a push button tool change (24vdc when the button is pushed). J4 LED is lit at all times. When connecting other sensors to J5 - J8, they are all "ON" regardless of sensor state.
Does the LED get brighter or dimmer when you press the button? The LED is supposed to turn on when the input on the "4" terminal is close to the voltage on the "<" terminal. The LED is supposed to turn off when the input on the "4" terminal is greater than 3.8V above the "<" terminal (see the PMDX-10-Input User's Manual, just above the warning box on page 6 and the input specs in section 9).
Having the LED on all the time sounds like one of two things:
1 - you have the 0V wire on the "4" instead of "4<" terminal (yeah, I know you said you had it connected to the "<" terminal
2 - somehow your button/sensor it has a significant leakage current when the button is not pressed.
The second way is to power the sensors with a completely independent 24vdc power supply. I connect 0vdc from the PS to <J4 and J4 is the sensor wire from the push button tool change. When I push the button, the LED is lit!!!! Success!!!
Maybe. You said above that the button is supposed to output 24V when pressed. But when 24V is present into the PMDX-108 the LED should be off.
Here is a test: With the PMDX-108 powered (via ribbon cable from your SS?), take your 24V supply and connect the 0V (gnd) terminal to the "<" terminal on J4 with nothing connected to the "4" terminal. The LED should be off. Short the "4" terminal to the "<" terminal and the LED should turn on. Disconnect the"4" terminal from the "<" terminal and connect the "4" terminal to the 24V output of your supply (with the supply turned on). The LED at J4 should remain off.
The same should hold for J5 through J8 (all of the "<" terminals are tied together on the PMDX-108-Input board so you don't need to move the 0V wire from your 24V supply).
