Britannica
Sources used in this answer
What is the phantom ring in a Sperry gyrocompass?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
gyrocompass
The gyrocompass aboard the National Oceanic and Atmospheric Administration's (NOAA) ship Rainier. Gyrocompasses are navigational instruments that use a continuously driven gyroscope to accurately seek the direction of true (geographic) north.
In a Sperry gyrocompass, the phantom ring is a critical component that surrounds the vertical ring, which houses the rotor case.1
The vertical ring is pivoted within the phantom ring, and its weight is supported by steel wire strands suspended from the phantom head. To ensure accuracy, a follow-up system is employed to keep the phantom ring continuously aligned with the vertical ring. This alignment is essential because it prevents torsion in the suspension wires and minimizes support friction around the vertical axis. Additionally, the compass card is mounted directly on the phantom head, and the mercury ballistic frame is pivoted to the phantom ring.1