Proximity Switch

Testing circuit?
there is a proximity switch which is of 2 wire type,powered by 13.1v dc when in circuit ,has coil resistance 13 ohm.its inductance varies when a ferrous target is brought near to it.
with target far inductance is 4.6 to 4.8, with target near inductance increases to 5.6 to 5.8mH.I WANT TO DESIGN A TESTING CIRCUIT OPERATING AT 12V DC USING TRANSISTOR & LAMP . LAMP SHOULD ILLUMINATE WHEN TARGET IS BROUGHT NEAR ASBOUT 60 TO 80 THOU.CAN ANY BODY HELP? PLEASE SEND CIRCUIT DIAGRAME.
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