Magnetic permeability sensor for using a single sensor to detect magnetic permeable objects and their direction

A method comprising:

• deploying one or more magnetically permeable objects into a tubular, wherein the tubular is disposed in a wellbore;
• and
• counting the one or more magnetically permeable objects that pass a sensor to produce a defined count, the sensor comprising:
• a first permanent magnet,
• a second permanent magnet, and
• a magnetic field sensor disposed between opposing poles of the first permanent magnet and the second permanent magnet.

A system comprising:

• a downhole tubular having a sidewall joining a sensor housing;
• a magnetic sensor disposed within the sensor housing, the magnetic sensor comprising:
• a first permanent magnet;
• a second permanent magnet;
• a magnetic field sensor disposed between opposing poles of the first permanent magnet and the second permanent magnet;
• and
• a circuit connected to the magnetic field sensor, the circuit configured to
• count one or more magnetically permeable objects that have passed by the magnetic field sensor, and
• determine direction of the one or more magnetically permeable objects based on an output of the magnetic field sensor;
• and
• an electrically triggered device coupled to the magnetic sensor.