Hi,
Can you just connect the sensor up to your 24V supply on its own, no arduino connected, and measure the output volts when the sensor is detecting and not detecting please.
A picture of the sensor would be a help.
Tom.... 
Hi,
Can you just connect the sensor up to your 24V supply on its own, no arduino connected, and measure the output volts when the sensor is detecting and not detecting please.
A picture of the sensor would be a help.
Tom....