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Dan,
I have spent the past week working on
integrating a Compass / Magnetometer /Linear dual
Axis Tilt System into my psub's PLC. I will share my experience with this
unit.
The sensor is from a company called ADVANCED
ORIENTATION SYSTEMS, the model is the EZ-Compass-3/Magnetometer http://www.aositilt.com/Compass.htm.
The unit cost is $599.00. The unit is designed to give compass heading as
well as roll and pitch angles and temperature. The sensor board is
2" x 2.5" x0.75" and interfaces with a PLC via an RS232 connection.
The signal, which is refreshed every 250ms, is given as an ASCII string that
includes, pitch-angle, roll-angle, temperature, and compass
heading. After receiving the unit, I tested it by wiring it to my
laptop and using Hyper-Terminal to setup and integrated the sensor. All
worked fine just as documented.
As I am using a PLC to interface with all ship
systems and sensors, the next step was to plug the sensor into the PLC.
When I did this, I found that I needed to upgrade by PLC cpu module to be able
to both read and write an ASCII string. After installing the upgraded cpu,
I was able to configure one of the PLC communication ports to see the sensor.
I parse the ASCII string in my PLC ladder logic
to get the individual measurements which I in turn display on a touch screen
color display that interfaces with my PLC. An example, a typical ASCII
output string would be"$R-2.61P1.08T21.5X206.7Y95.4Z-367.5C43.9*4d".
The sensor can be configured to turn off any data elements that you are not
interested in. For my application, I turned off the X,Y and Z magnetic
vector components as I was only interested in the compass azimuth
value.
As any magnetometer will be
effected by the steel in the hull, I am planning on mounting my unit external to
the hull behind the pilot viewport in an non ferrous, water
tight pod. The unit will not work inside the hull. By moving
the sensor into proximity of the hull, I can definitely tell when the steel of
the hull starts to influence the signal. The documentation for the unit
has both "hard iron" and "soft iron" calibration procedures for
nulling out the effect of the hull. This is done while boat, with
sensor attached, is rotated slowly 360 degrees. As I have not done this
calibration yet, I can not comment on its effectiveness. So far all the
components of the sensor are working fine as documented. I know
there are a number of companies that make similar sensors. This is been my
experience with this particular sensor to date. So far, so
good.
Cliff
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