Gyro Compass

 Gyro Compass 

Gyro compass is used to provide an accurate non magnetic directional reference with respect to true north 

Principle 

Nucleus of gyro compass equipment is an electrically driven gyroscope , which has a heavy well balanced wheel spinning at a high rate above 20000 rpm and has a  freedom of movement in three perpendicular axis . ie) free to turn about its spinning axis , its vertical axis (tilt )  and horizontal axis ( Azimuth) .

The whole system is balanced so that the center of gravity is at the point of intersection of three axis.

Properties of Gyroscope 

*  Gyroscopic inertia or rigidity in space 

*  Precession 

1)  Gyroscopic inertia causes it to maintain its position in space irrespective of any movement and to resist any force tending to turn its spin axis in a new direction .

2) Precession is the angular displacement of the spin axis of the gyroscope when a torque is applied to its spin axis the resulting movement will be in a direction at right angles to the applied torque . the angle being measured in the direction of spinning wheel.

Gravity control in Gyro 

By top heavy effect and bottom heavy effect

[ The rotation of earth given us free gyroscope , which has to be controlled with the help of precession and we have to use the property of earths gravity and rotation to create the torque. if we place gyroscope with its north axis pointing eastwards this axis will tilt upwards as the earth rotates and with the help of mercury ballistic or a fixed weight we can now create a top heavy effect which will provide us a torque . this is achieved where the rotor is moving in  anti clockwise direction and north end pointing eastwards as the earth rotates this end will tilt upwards hence mercury from north bowl N flows to the south bowl S and as a result torque is applied to the upper end of the axle at B which results in Precessing north end westwards. 

Making Gyro North seeking 

By damping in tilt and damping in azimuth 

damping in tilt in case of top heavy effect 

damping in azimuth in case of bottom heavy effect 

To produce a compass we must produce an  instrument which will seek and settle in the meridian and if disturbed from the meridian will return to it 

In general this is done by creating a torque about the horizontal east west axis which produce a precession in azimuth and causes the spin axis to seek the meridian .

Advantages of Gyro 

High reliability 

Compact size

Small errors 

Ability to run repeaters and provide heading references 

Errors of gyro 

Latitude error ( damping error ) 

Course and speed error ( steaming error) 

First rolling error 

Inter cardinal rolling error 

Ballistic deflection 

Ballistic tilt

Performance Standards 

*

  When switched on in accordance with manufacturers instruction the compass shall settle within six hours in latitude of up to 60 deg 

*  The settle point error at any heading and at any latitude up to 60 deg shall not exceed 0.75 X sextant latitude 

* Means of illumination with dimming control          

*  Lubber line aligned carefully in the fore and aft direction 

*  Compass card should be graduated at intervals of one deg and every tenth graduation shall be marked with numeral.

Do Subscribe, for regular updates

Good luck.