Sensors not getting power

We have a robot that we have repurposed from a depalletizing cell and are now trying to use in a new palletizing operation. The new palletizer is very simple using 2-IR sensors and a switch for a pneumatic cylinder. di/do 0/1 were being used for the sensors and do2 was being used for the cylinder.

The palletizer was working for approximately 3 months before the sensors no longer were powering on, for what seemed like no reason. I know that the robot and the DI/DO is getting power from checking with the multimeter, the fact D02 works fine and can be activated to turn on the air to the cylinder, and whenever I disconnect the sensors from the terminal blocks- I can get one of them to power on when held directly to the DI0 contacts. Additionally, if I disconnect the terminal block and only put the sensor back into DI0, that sensor will power on for a minute or two and be usable, before turning off again.

This is an image of the original wiring, from the depalletizing cell the robot was taken from. It utilized a set of external start, stop, reset buttons we are no longer using, as well as more IO for the rest of the cell systems.

When the robot was installed in the new cell, only the 2 sensors and the pneumatic switch were needed, and the wiring was simplified. I do not believe there has been any change in the wiring since it was installed, however I cannot confirm.

I have been told that it is potentially a problem resulting from removing the external start/stop/reset buttons, but do not know how to confirm this. Has anyone else experienced similar problems in the past?


Well. First off, the internal 24V supply in the controller is not connected to the IO. That’s the Power terminals:
PWR is internal 24V
GND is internal 0V,
24V is for powering all IO 24V
0V is for grounding all IO

From the factory, the PWR terminal is connected directly to the 24V terminal and the GND terminal is connected directly to the 0V terminal.

Right now, you do not have the internal 24V supply powering the IO. You have two external wires connected, though, so that could be 24V from an external 24V supply, which isn’t working anymore? :slight_smile:

Thanks for your input.

The sensors actually ended up both just being bad. Wiring I thought was okay due to how long it ran and the DO still having power while the DI did not seem to.

I still don’t think your setup is ideal, if the two wires going into 24V and 0V on the Power terminals are not coming from a 24V power supply (which it looks like it isn’t).
That means the controller is sourcing its 24V from some other component (maybe the bigger multicolored cable), and you could quickly run into overloading that 24V supply if it’s not intended for powering other stuff than itself. :slight_smile: