ivo how did you come up with the "B = sensor so I can learn something
I have never seen any reference to that before
I know the br bl are power in, the diode with arrow pointing away is a standard for opto diode or LED the output looks like it is complimentary pare output but I can't make out the color of the output wires. that color can be an indication of the function or not depending on the manufacture
I always thought the label outside of the symbol is just an identifier on the print
the complete circuit would be helpful to see how it's used