Figure 1-3.—Pulse counting accelerometer

Figure 1-2 shows an E-transformer accelerometer, while figure 1-3 shows a pulse counting accelerometer. Two accelerometers (orientated North- South and East-West, respectively) are mounted on a gyro-stabilized platform to keep them in a horizontal position despite changes in ship’s movement. The accelerometers are attached to the platform by an equatorial mount (gimbal) whose vertical axis is misaligned parallel to the earth’s polar axis. This permits the N-S accelerometer to be aligned along a longitude meridian and the E-W accelerometer to be aligned along a latitude meridian. Figure 1-2.—E-transformer accelerometer. A three-gyro stabilized platform is maintained in the horizontal position regardless of the pitch, roll, or yaw of the ship. Figure 1-4 shows a gimbal-mounted gyro. Ship’s heading changes cause the gyro signals to operate servo system motors, which in turn keep the platform stabilized. High-performance servo systems keep the platform stabilized to the desired accuracy. (You will find in-depth information on accelerometers, gyros, and servo systems in NEETS Module 15, Principles of Synchros, Servos, and Gyros.). Maintaining this accuracy over long periods of time requires that the system be updated periodically. This is done by resetting the system using information from some other navigation means; i.e., electronic, celestial, or dead reckoning. Figure 1-3.—Pulse counting accelerometer. Several models of SINS are in use. In general, AN/WSN-2 systems are installed on auxiliary ships, AN/WSN-2A systems are installed on submarines, and AN/WSN-5 systems are installed or being installed on surface combatants. In the following paragraphs, you will be introduced to the AN/WSN-5 SINS and its advantages over these earlier systems. Figure 1-4.— Gimbal-mounted rate gyro. 1-4