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Maretron Compass Calibration

Our current favorite compass for use with the Ockam system is the Maretron SSC200. It is a 3-axis turn-stabilized electronic compass, and is relatively inexpensive. It is also widely available, so it can be obtained fairly easily (including through our Web Store). It can also be calibrated for deviation using a variety of methods, so it is rather flexible in actual use, unlike many other compass types.

One method requires a connection to a PC for serial communications. However, this method is not very practical unless you are very comfortable with working with this type of low-level hardware configuration. It requires a certain familiarity with electronic hardware and software, so it is not suitable for everyone. Even those who are well-versed in this type of work find it to be a bit of a bother. Personally, I avoid this method when possible.

Another method requires the use of one of Maretron’s proprietary displays. This method has the clear advantage of ease-of-use, but the display itself is a little expensive (USD 800 retail price). Some people have installed this display as a heading repeater for the steering station (like with the KVH AC100) and gotten the additional calibration functionality as a bonus. Most people do not want to incur the additional expense, so this is not usually a viable method. Some servicing dealers happen to have a DSM200 for use in calibration, so you may be able to arrange something with them if you want to go this route.

By far the most popular method is the simple power-on calibration method. The SSC200 will perform a calibration after power-on when a few simple steps are followed (see page 11 of the current SSC200 manual). This is probably the simplest method, but feedback can be a problem. The compass will indicate a successful deviation calibration by sending the compass headings 000, 090, 180, and 270 each for two seconds, followed by the actual heading. If you had a direct indication of the compass heading, this would not present much of a problem. However, the Ockam system typically has some sort of averaging set for the display data, so this confirmation message can get masked by the display averaging.

The best way to get around this is by setting the display averaging for heading to zero on a T1 processor. This forces the system to display the information as it receives it. The display averaging for heading can be set through a computer connected to the Ockam system; this option is unfortunately not available through a Matryx display. The command to set heading to zero display averaging is A23=0 with a direct command through a terminal session. Display averaging can also be set on the OckamSoft driver through the Control tab under the Avgs radio button by entering 0 in the Val box and clicking the Execute button.

The 001 Unisyn processor cannot have a display averaging value set lower than 0 or anything other than an integer, so the lowest value is 1. You may be able to catch the Maretron confirmation sequence with this, but it is not likely.

Regardless of the processor used, you should set the display averaging back to the value it was before. The default value for heading averaging is 1 second, so the command is A23=1 if setting by direct entry.

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