# Specific 3D Printers, Scanners, & Hardware > CTC 3D Printers >  CTC prusa i3 pro B  Auto bed leveling

## forbesbrb

Hi all has any one ever fitted this printer with a probe like this LJC18A3-H-Z/BX 1-10mm Capacitance Proximity Sensor Switch NPN NO DC 6-36V 300mA 
if you have can you please help a novice who is stuck i have fitted the sensor to the printer and i have wired it but on the signal wire i get 0 volts that  can't be correct I thought i would need at least 5 volts i just don't know what i have done wrong.

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## noiseboy72

So long as you have the polarity correct, then yes I agree, you should see a voltage when at the correct height. Are you using the resistor method to connect to the Z stop and have you connected it correctly?

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