Each G-882 will have slightly different scale and bias values from one another. Meaning it is not possible to use the scale and bias values from another G-882, even if the same altimeter is used in both fish. If an altimeter is replace with one of a different range, say 50m 200KHz, then the scale and bias will have to be recalculated, which is time consuming especially when companies are managing over eight magnetometers on a vessel.
To eliminate the requirement for scale and bias values Geomatrix (endorsed Geometrics inc) developed the Digital Accessory Board which passes the digital altimeter value and digitises the depth, pitch and roll measurement, eliminating the need to enter scale and bias values and the quality checks that go with it.
Developed by Geomatrix Earth Science ltd endorsed by Geometrics Inc.
The new Geomatrix upgrade exploits the digital output from auxiliary devices and appends them to the standard G-882 serial sentence. Including the Depth sensor, Altimeter, Pitch and Roll. Each channel can be appended with a suffix to assist with identification, alternatively the suffix can be toggled off to maintain the traditional G-882 sentence.
To accompany the Digital Accessory board Geomatrix developed a simple console for managing active channels, zeroing the depth measurement (Null), and programming the instrument baud rate and sample rate.
If the Altimeter value is reported as a 4 digit integer then the G-882DIGTIAL board is programmed to report altimeter distance in decimetres or feet. Connect the G-882DIGITAL to the Digital console program and reprogram the G-882DIGITAL board to report the altimeter distance in meters.
G-882DIGITAL Altimeter value reads 0m at full range
the value the altimeters reads at full range depends on the make and model of the altimeter in use.
Tritech altimeters commonly report 99.99m at full range, but not always. When the Tritech altimeter was ordered the customer may not have specified that the altimeter will be sued with a G-882. as a result it may have been calibrated with the full range full range at 100m not 99.99m. The DIGITAL board only passed 4 characters AA.aa and therefore will report 0m if the altimeter full range is 100.00m.
Signal strength below 400 in one heading and above 400 in the opposite heading. Sensor orientated at 45 degrees as per CSAZ solution for location.
Check the version of CSAZ. It needs to be the latest version which uses the World Magnetic Model (WMM) and not an old version using the IGRF model.
In the southern Baltic Sea CSAZ may suggest the optimal orientation for the G-882 Sensor is 45 degrees when surveying along a North-South heading, as seen in the following CSAZ solutions. However take care, keeping the sensor orientated vertically still produced an acceptable solution because the shaded green area is beyond the bold circumference located at 15◦ inclination (indicated by the purple arrow). If the green shaded area is over this line then the G-882 should achieved a signal strength over 400.
If in doubt also try the G-882 orientated vertically. Do not blindly follow CSAZ solution as the tool as limitations.
CSAZ assumes a uniform earth magnetic field. In a marine deployment the earths magnetic field may be being distorted by some ferrous objects. This could be the large magnetic field of the vessel or smaller magnetic fields on the frame. Is the signal strength is dropping below 400 in one heading but no the opposite heading then it could be the magnetic field around the sensors is changing. All induced magnetic fields will orientate to magnetic north. Therefore the sensor(s) will reside in a different part of the vessels or frames induce magnetic field when heading north compared to south. It could be that the magnetic influence of the vessel or frame could be just enough to push the earths magnetic field into a dead zone. Check all hardware on the frame is non ferrous and the offset of the frame to the vessel.
Why am I unable to Configuring MagLog with two concatenated G-882DIGITAL
When using G-88x/823 input device it is not possible to enable Sensor 2,3,4…. in a concatenated group of G-882DIGITAL. Only the first G-882DIGTIAL in the concatenated sentence is available.
Run MagLog and navigate to Configure -> Device buffers and settings then disable (uncheck) the Configure 88x magnetometer(s) for each survey option which will allow the user to freely set which Sensors are active or disabled.
Configure 88x magnetometer(s) for each survey option has to be turned off because the G-882/823 Configuration tool has been replaced by the G-882DIGITAL console program.
One of G-882/823 Configuration functions was to count the number of magnetometers which are present in a concatenated group. Because the G-882/823 Configuration tool cannot program the G-882DIGITAL instruments the software is unable to count the number of magnetometers in a concatenated group. As a result the OK button is unavailable (greyed out) and the only option is to cancel out of the window which in turn disables the ability to turn on additional sensors in the 88x 823 Settings window.
By disabling G-882/823 Configuration MagLog relies on the user to define the number of concatenated magnetometers within a group and define the number of channels for each sensor.
If the G-882DIGITAL are run in bypass mode G-882/823 Configuration will be able to communicate with the G-882, but Depth, Altitude, Pitch and roll will be unavailable because they are wired directly to the G-882 DIGITAL Accessory Board
An acoustic transponder which fits into the head of the G-882 tow fish to report the height of the fish above the sea bed in real-time.