Apparatus for determining the phase difference between the rolling oscillation of a ship and a liquid contained in a stabilizing tank

Apparatus for determining the phase difference between the roll oscillation of a ship and the oscillation of a liquid contained in a stabilizing tank wherein means are provided to obtain an output proportional to the roll rate of the ship and the measured liquid level difference in the stabilizing tank and means provided to adjust the liquid level in the tank in response to a command signal comprising:

• a. first means for forming a derived roll angle, having a frequency dependent phase shift relative to the true angle, from the measured roll rate;
• b. second means for forming a derived liquid level difference from the measured liquid level difference having the same frequency dependent phase shift as the derived roll angle relative to the true roll angle;
• c. means for comparing the outputs of said first and second means to develop an analog measuring voltage dependent on the phase difference between the roll angle and the liquid level difference, said analog measuring voltage being the control voltage and being provided as a command signal input to the means provided to adjust the liquid level in the tank comprising:
• 1. a first comparator having its input coupled to the output of said first means and providing a first output signal at one level when its input is positive and at another level when its input is negative;
• 2. a similar second comparator coupled to the output of said second means providing a second output signal;
• 3. logic means for the formation of first and second time signals through the logic addition of the said first and second output of said first and second comparator signals and one of said first and second output signals and the inverse of one of said first and second output signals;
• and
• 4. means for forming from said time signals an analog measuring voltage dependent on the phase difference between the roll angle and liquid level difference.