Unusual Problem Solved
During initial tests in the laboratory, signal errors continuously occurred. These events were easily detected by the sound of the servo gears rotating in small increments. The source of this noise was found to be due to the metal material in the pockets of the lab technicians as they passed within 6 feet of the unit.
This Airpax electromagnetic compass was designed for deepsea temperatures measurements at depths to 10,000 feet, where pressures can reach 5,000 psi. This allowed operation in the Tongue of the Ocean in the Bahamas.
The cannister is designed to withstand these high pressures by mounting it in a cannister 7 inches in diameter by 17 inches long. Note the thickess of the wall and the double "O-rings".
The cost of cables capable of withstanding the rigors of the dynamic ocean can be quite expensive, exceeding $2,000 for a single wire for a length of 10,000 feet. Therefore, signal and power are transmitted on a single pair of wires. The two-wire connector can be seen at the bottom of the unit in the left picture. The signal output is an FM signal whose frequency is proportional to bearing. A single IRIG FM carrier channel is used for signal transmission and detection.
The compass sensor at the right is a magnetic flux valve type in the picture on the right. The output signal is extremely linear over the full 360 degree bearing range. There are three pickup coils, mounted on a damped pendulum and spaced at 120 degree angles that provide a three-phase output. The amplitudes of the three phases provide the bearing information. An electromechanical servo drives a potentiometer that controls a VCO that generates the IRIG frequency signal.
The next project is a Sheet Metal Fabrication Control System
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