There are no openings or windows in the block.
This was sent to us by a client, who also does not know what it is, just that it no longer works. I don't have access to the factory, if I did this would be much much easier.
The parameters I was given is that it activates (fills the tank) at 50mm from the sensor(s), and de-activates (stops filling) at 20mm from the sensors.
The arm sits above the tanks.
My first thought was why not have one sensor inside the tank, but this does not work because it is used on different inks, colors, etc.
A capacitive sensor has only 2 states, on or off, so this other little block must be a sensor of some sort - just no idea what.
The capacitive would do the 20mm "top" end of the open tank, so this other sensor would do the lower end, 50mm sensing distance.
I don't think it would be magnetic or thermal. Ultrasonic is a possibility, the sensing distance works, but I don't see how such a closed box could be ultrasonic.