Arrangements for correcting compasses
First Claim
1. A method of correcting the output of a marine gyro compass comprisingapplying a first signal representative of the speed of a ship to a signal processor,applying a second signal to the signal processor representative of the output of a marine gyro compass,producing an output signal being a corrected marine gyro compass output, the corrections being corrections capable of expression by virtue of differential equations and which are solved by numerical method by taking small but finite time increments to linearize the equations with regard to time, the correction factor being updated in this way at regular time intervals,effecting an initial procedure to feed into a semipermanent data store cooperating with the signal processor values corresponding to a limit of measurable tilt in the gyro compass and said output signal is produced by calculating the rate of change of the tilt up to said limit, the tilt when beyond the limit being also calculated, andstoring values corresponding to the following in said initial procedure:
- the damping characteristic in the gyro compass, the period term for the damped oscillations in the gyro compass following movement to a new position, and a function representative of the viscosity of the fluid in the tilt determining mechanism of the gyro compass.
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Accused Products
Abstract
A marine gyro compass output is corrected to take account of accelerationscting upon the ship in which it is installed by calculating about once per second a correction capable of expression by differential equations which are solved by numerical methods by taking small but finite time increments to linearise the equations with regard to time, the current calculated correction factor being applied to correct the gyro compass output many times per second. The corrections can take into account (a) ship north-south acceleration, (b) change in Coriolis acceleration, (c) earth rotation rate and (d) azimuth error for east-west speed. Furthermore, account can be taken of the constant characteristics of the particular gyro compass to be corrected in terms of its tilt limit, its period of damped oscillation, its damping and the characteristics of the compass electrolytic level which determines tilt.
34 Citations
16 Claims
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1. A method of correcting the output of a marine gyro compass comprising
applying a first signal representative of the speed of a ship to a signal processor, applying a second signal to the signal processor representative of the output of a marine gyro compass, producing an output signal being a corrected marine gyro compass output, the corrections being corrections capable of expression by virtue of differential equations and which are solved by numerical method by taking small but finite time increments to linearize the equations with regard to time, the correction factor being updated in this way at regular time intervals, effecting an initial procedure to feed into a semipermanent data store cooperating with the signal processor values corresponding to a limit of measurable tilt in the gyro compass and said output signal is produced by calculating the rate of change of the tilt up to said limit, the tilt when beyond the limit being also calculated, and storing values corresponding to the following in said initial procedure: - the damping characteristic in the gyro compass, the period term for the damped oscillations in the gyro compass following movement to a new position, and a function representative of the viscosity of the fluid in the tilt determining mechanism of the gyro compass.
- View Dependent Claims (2, 3)
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4. A method of correcting the outut of a marine gyro compass having an electrolytic level indicator comprising storing in a signal processor data representative of a limit of measurable tilt in the level indicator, a damping factor (DMP) for the level indicator, a period term (PER) for the level indicator, and a constant (K) being the viscosity characteristic of the electrolytic level indicator,
applying a first signal representative of the speed of the ship to the signal processor. applying a second signal to the signal processor representative of the output of the marine gyro compass, and producing an output signal corresponding to the output of the marine gyro compass corrected by a correction factor by taking into account said input data and first and second signals by solving the following differential equations by numerical methods; -
space="preserve" listing-type="equation">EDD=-PER.EES-EE.Φ
V.cos(LAT)+VE.tan(LAT)/RG
space="preserve" listing-type="equation">EED=-DMP.EES+ED.Φ
V.cos(LAT)
space="preserve" listing-type="equation">EESD=K(EE+AN/G-EES)the solving of the equations being effected by taking small but finite time increments to linearize the equations with regard to time, the correction factor used to produce the corrected output signal being updated at regular time intervals, in the above equations the following notation being used; AN;
ship north accelerationED,EDD;
azimuth error and error rateEE,EED;
tilt and tilt rateEES,EESD;
tilt signal and tilt signal rateG;
acceleration due to gravityDMP;
damping term of the level detectorPER;
period term of the level detectorK;
characteristic viscosity of the compasslevel detector LAT;
latitudeΦ
G;
earth angular rotation speedΦ
V;
Φ
G as corrected by east-west speedRG;
earth'"'"'s radiusVE,VN;
ship east and north velocity.
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5. A method of correcting the output of a marine gyro compass having a level detector in respect of which the damping factor (DMP), period term (PER) and constant value (K) dependent on the viscosity characteristic of the fluid in the level detector are known comprising/applying a first signal representative the speed of a ship to a signal processor, applying a second signal to the signal processor representative of the output of the marine gyro compass, and providing stored values in said signal processor corresponding to DMP, PER and K
producing an output signal being a corrected marine gyro compass output, the corrections taking into account errors represented by the following: -
(a) ship north-south acceleration modelled by the equation
space="preserve" listing-type="equation">EESD=K (EE+AN/G-EES)(b) change in Coriolis acceleration represented by the expression
space="preserve" listing-type="equation">VE.(VE/(RG.cos(LAT))+2.Φ
G).sin(LAT).(c) earth rotation rate for east-west speed given by
space="preserve" listing-type="equation">Φ
V=Φ
G+VE/(RG.cos(LAT)), and(d) azimuth error for east-west speed given by
space="preserve" listing-type="equation">VE.tan(LAT)/RG,wherein in the above expressions and equations the symbols have the following meanings; AN;
ship north accelerationED,EDD;
azimuth error and error rateEE,EED;
tilt and tilt rateEES,EESD;
tilt signal and tilt signal rateG;
acceleration due to gravityDMP;
damping term of the level detectorPER;
period term of the level detectorK;
characteristic viscosity of the compasslevel detector LAT;
latitudeΦ
G;
earth angular rotation speedΦ
V;
as corrected by east-west speedRG;
earth'"'"'s radiusVE,VN;
ship east and north velocityand wherein the corrections are capable of expression by the following differential equations;
space="preserve" listing-type="equation">EDD=-PER.EES-EE.Φ
V.cos(LAT)+VE.tan(LAT)/RG
space="preserve" listing-type="equation">EED=-DMP.EES+ED.Φ
V.cos(LAT)
space="preserve" listing-type="equation">EESD=K(EE+AN/G-EES)the differential equations being solved by numerical methods by taking small but finite time increments to linearize the equations with regard to time, the correction factor being updated in this way at regular time intervals. - View Dependent Claims (6, 7)
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8. Apparatus for correcting the output of the marine gyro compass having a level detector comprising
(a) ship speed input means for receiving a signal representative of ship'"'"'s speed (b) gyro compass input means for supplying a digital signal corresponding to the compass output to a processing unit (c) a processing unit responsive to the ship speed and gyro compass input means for providing an output signal being a corrected gyro compass reading, and (d) control means for controlling the processing unit to solve differential equations representative of the corrections to be employed by numerical methods and characterised by taking small but finite time increments for linearizing the equations with regard to time, and repeating the computation at regular time intervals.
Specification