Device for measuring the velocity of a magnetically receptive object

A device for measuring the speed of an object having a magnetically conductive element therein where said object moves along a predetermined path, said device comprising

• first means for forming a first standing oscillating magnetic field having a first predetermined natural frequency,
• second means for forming a second standing oscillating magnetic field having a second predetermined natural frequency,
• said first means and said second means spaced a fixed distance from each other,
• means for driving said oscillating fields formed by said first means and said second means,
• detector means for detecting a change in said natural frequency of said first means and said second means, and
• means for measuring the time elapsed between the successive detectable changes in said natural frequencies of said first means and said second means.

A device for measuring the speed of an object having a magnetically conductive element therein where said object moves along a predetermined path, said device comprising

• a first coil for forming a first standing oscillating magnetic field having a first predetermined natural frequency,
• a second coil for forming a second standing oscillating magnetic field having a second predetermined natural frequency,
• said first coil and said second coil spaced a fixed distance from each other,
• means for driving said oscillating fields formed by said first coil and said second coil,
• a phased locked loop for generating a DC voltage indicative of steady state frequencies of said standing oscillating magnetic fields formed by said first coil and said second coil and for generating a spike indicative of a change in frequency of one of said first predetermined frequency and said second predetermined frequency,
• a comparator for identifying a spike indicative of a magnetically conductive material in one of said fields, and
• a clock for measuring the time elapsed between the successive detectable changes in said natural frequencies of said first coil and said second coil.