Importance of maintaining separation of heading sensor from magnetics

[Chuck - Raymarine - Moderator]

Importance of maintaining separation of heading sensor from magnetics

Raymarine autopilots are designed to sense magnetic north and utilize magnetic heading data. In the case of Evolution autopilots, the magnetic north sensing component is the EV-1 Sensor Core. In the case of many earlier autopilot designs the magnetic north sensing component was a fluxgate compass transducer. Like the vessel's compass, the autopilot's magnetic north sensing component should not be located within close proximity to objects or structures producing magnetic fields. Objects or structures producing magnetic fields which are located in close proximity to a compass or autopilot's magnetic north sensing component will cause deviation in the sensed heading. While compasses and the autopilots may be configured to compensate for some degree of magnetic deviation, there are limits to the amount of compensation which may be configured within a compass or autopilot. For best autopilot performance, it is recommended that the maximum deviation sensed by the autopilot's magnetic north sensing component not exceed ten degrees.

Accordingly, the mounting location of the autopilot's magnetic north sensing component should be carefully chosen, it should not be located within three feet of any sources of magnetism (ex. ferrous materials (fasteners, engine blocks, anchors, tools, tin cans, etc.), electric motors (compressors, winches, thrusters, etc.), speakers, mobile 'phones or high current carrying conductors). Always check on the other side of bulkeads and large ferrous masses like engines or keels can have a much larger effect than expected.

In the case of vessels constructed with steel hulls, it is not uncommon for the autopilot's magnetic north sensing component to be installed above decks on mast or hard top. The area of the autopilot magnetic north sensing component's mounting location should labeled to indicate the presence of the magnetic sensor and should be regularly inspected to ensure that objects constructed from ferrous materials or magnets have not been stored nearby.

One common tool used for detecting magnetic fields is a handheld compass. Should the compass needle/card deflect as it is moved into the proximity an object, then the object may be considered to produce a magnetic field. Similarly, a magnet may be used to test for or ferrous metal. Should a magnet be attracted to or be deflected from an object, then the object may be considered to produce a magnetic field. One of the latest additions to tools for detecting magnetic fields is the Magnetometer function Gemeco's free iNstall app for smartphones. It is recommended that such testing be performed prior to permanently mounting the autopilot's magnetic north sensing component. When seeking an installation location for a magnetic north seeking device such as an autopilot compass, instrument compass, etc., it would be considered a best installation practice to test the magnetic field strength in the intended location while all onboard electrical devices are on (and cycling in the case of devices with electrical motors). While Raymarine has not specified a maximum sensed magnetic field strength value, verifying the iNstall's app's magnetometer needle is in the green band (+/- 10 µT) would be a good starting point.

Note that there is no form of screening (Lead box, wire mesh etc . .) that can be installed around a compass sensor to eliminate the effects of external deviating fields, in such cases where excessive deviation is encountered, relocation of the sensor is the only option.

RAYFAQ#