001_2010 GPS Gyro SPS-461

FSINPVT FIELD TIP – 001/2010

GPS Gyro – SPS 461

Setting Up of antenna:-

1. Set up the antennas as far as physically possible – atleast 3m apart.

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GPS Antenna 1 for Position

Radio Antenna

Antenna 2 for Vector & Heading

• Ethernet with PoE connectivity to a 10/100 Base-T network through an RJ45 jack on a multiport adaptor (P/N 57167) or cable (P/N 65791-00).

• Primary power from a Trimble AC/DC power supply (P/N 62546) using the multiport adaptor (P/N 57167) or cable (P/N 65791-00).

• Full 9-wire RS-232 serial communications using the 26-9-pin multiport adaptor (P/N 57168) or a 26-pin serial communications cable (P/N 65791-00)

• 1PPS, 2 x RS-232, input DC, Ethernet cable (P/N 65791-00)



2. The antennas should ideally be in the same height. If that can not be achieved, measure the height of antenna from any reference level and enter them in the set up page for each antenna.

3. The antennas should ideally be mounted in the fore and aft position of the vessel, preferably along a known reference line.

4. By default, the heading is measured from Vector antenna 2 to Positioning antenna 1. But this settings can be changed to read heading from Positioning antenna 1 to Vector antenna 2

Specifications :-

Code Differential GPS PositioningHorizontal accuracy 0.25 m + 1 ppm RMS (0.8 ft + 1 ppm RMS)Vertical accuracy 0.50 m + 1 ppm RMS (1.6 ft + 1 ppm RMS)

OmniSTAR PositioningVBS service accuracy Horizontal <1 m (3.3 ft)XP service accuracy Horizontal 0.2 m (0.66 ft), Vertical 0.3 m (1.0 ft)HP service accuracy Horizontal 0.1 m (0.33 ft), Vertical 0.15 m (0.5 ft)

Real-Time Kinematic (RTK) PositioningHorizontal accuracy 10 mm + 1 ppm RMS (0.032 ft + 1 ppm RMS)Vertical accuracy 20 mm + 1 ppm RMS (0.065 ft +1 ppm RMS)

Precise HeadingHeading accuracy

02 m antenna separation 0.09° RMS10 m antenna separation 0.05° RMS

RECEIVER SET UP

Receiver Status – Vector Heading

The vector heading information includes:

Heading – The current heading and heading configuration.

Adjusted Heading – Adjusted heading in degrees after adjustment and direction have been applied

Heading Adjustment – Heading adjustment in degrees.

Raw Heading – Raw heading in degrees before any adjustments have been applied

Slope Distance – The length of the vector from the AFC of the Base antenna to the AFC of the Rover antenna, given in meters.

Solution type – Current RTK solution of the internal vector. Either RTK Fixed or Float RT

Direction – The direction of the internal vector for heading, either Normal (From Vector antenna to Position antenna) or Reversed (From Position antenna to Vector antenna)

Antenna Configuration

Use these settings to configure the antenna or antennas (SPS461) that is used with the receiver.

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The SPS461 receiver uses two GPS antennas. All data relating to position, references the Position (POS) antenna. The Vector (VECT) antenna is used only to provide vector information such as the heading and attitude.

Antenna Type – Select the type of antenna being used with the receiver.

Antenna Serial Number – Enter the serial number of the antenna being used.

Antenna Measurement Method – Select how the antenna height is being measured.

Antenna Height [m] – Enter the measured height of the antenna. This is typically measured from a ground marker or the mounting point of the antenna.

Vector Configuration

Use this page to set receiver settings for the Vector when using a dual-antenna system.

Heading

Heading Adjustment – Heading adjustment in degrees.

Apply adjustment to – Select if the adjustment is to be applied to all heading outputs or only the NMEA HDT.

Direction – Set the direction of the internal vector for heading, either Normal (from the Vector antenna to the Position antenna) or Reveresed (from the Position antenna to the Vector antenna).

Attitude

Slope Adjustment – Enter the slope adjustment, in degrees, manually. Alternatively, if one of the calibration options is selected, it will be automatically calculated.

Calibration Options – When enabled, you can calibrate the vector by calculating the slope adjustment based on one of the following criteria:

from Raw Slope – When you click Recalculate, the current slope angle is set to zero.

from Antenna Delta Height – Enter the delta height in meters from the antenna phase center (APC) of the Position (POS) antenna to the APC of the Vector (VECT) antenna. For example, if the POS antenna is higher than the VECT antenna, you should use a negative delta height to adjust the slope to zero.

Recalculate – Click Recalculate to perform an instant recalculation of the slope adjustment. This is useful if you are using the from Raw Slope calibration method on a moving vessel.

Direction – Set the direction of the internal vector for the slope, either Normal (from the Vector antenna to the Position antenna) or Reversed (from the Position antenna to the Vector antenna).

Orientation – Set to either Pitch or Roll depending on the orientation of your antenna baseline with respect to the vessel centerline. This setting is also used to determine which field is populated in Attitude output messages such as the NMEA AVR.

Minimum Solution Type – Set this to determine the precision of the Vector solution. For the highest precision, set it to RTK Fixed.

Following pages discuss the best practice and calibration process of the SPS461 GPS Gyro

Alignment Option 1

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Bow AntennaPosition/Vector

Stern AntennaPosition/Vector

Observer, in line with Antennas

Observed angle to Sun from Reference Baseline

Reference Baseline. observer in line with both Antennas. Baseline parallel to Vessel’s fore & aft line



Method of Alignment and Best Practice (Option 1)

1. Install the antennas as far apart as possible (recommended 10m, if not then atleast 3m apart) in forward and aft direction of the vessel and in line or parallel with the fore and aft line of the vessel.

2. Position observer (if possible) in line with the antennas as shown in the figure above. Observer as far from stern antenna as physically possible to get a better in line alignment. Make an OT for observer position for logging.

3. If a Gyrocompass is present onboard vessel a comparison can be made. In that case switch on the Gyrocompass and after settling for 1 hour, start Gyrocompass logging. Start logging for observer OT position.

4. Ideally the vessel should be as steady as possible and not making any headway.

5. Carry out Sun observation every 1 minute for about 20/25 observations. Make sure the heading data from GPS Gyro is being logged at 1 Hz during the observation.

8. Calculate the baseline azimuth from Sunshot and use the proper survey form to document the alignment.

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Alignment Option 2

Method of Alignment and Best Practice (Option 2)


2. If the antennas can not be installed inline or parallel to the vessel’s fore and aft line, mark out a convenient Baseline (as long as Possible) and make that baseline parallel to the vessel’s fore and aft line. Carry out Sun observation with reference to that baseline. Carry out about 20/25 observations every 1 minute apart.

3. If a Gyrocompass is present onboard vessel a comparison can be made. In that case switch on the Gyrocompass and after settling for 1 hour, start Gyrocompass logging. Start logging for observer OT position.

4. Once a base line azimuth has been established from Sunshot, carry out a Taped offset measurement to define the baseline azimuth between the 2 antennas. Make sure that heading data from GPS Gyro is being logged during the taped offset measurement.

5. Use proper survey forms for recording and reporting the event.

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Bow AntennaPosition/Vector

Stern AntennaPosition/Vector

Observer position (OT)

Observed angle to Sun from Reference Baseline

Reference Baseline. Parallel to vessel’s fore and aft line

Measure Distance by tape

Measure Distance by tape



Alignment Option 3

Method of Alignment and Best Practice (Option 3 – quick method)


2. Measure the distances from vessel centerline to the centre of the antenna as shown in the figure above in A and B.

3. As per A, the C-O angle between vessel fore and aft line and Antenna Vector line is :

= tan -1 (3/10). To get corrected heading the “Theta” (angle) needs to be subtracted from Raw heading.

4. As per B, the C-O angle between vessel fore and aft line and Antenna Vector line is :

= tan -1 (2/7). To get corrected heading the “Theta” (angle) needs to be added to the Raw heading.

Note : Always draw a picture of your antenna position with respect to Vessel’s fore and aft line. Then the sign convention for applying C-O becomes much clearer.

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10m

3m 2m

5m

7m

4m

2m

A B



Notes:-

1. Position antenna and vector antenna are both same antenna and only difference is when you connect it to TNC 1 or TNC 2.

2. Antenna connected to TNC 1 will give position output. Antenna connected to TNC 2 will give Vector and heading.

3. By default heading is calculated From Position Antenna to Vector Antenna. But this setting can be reversed and a reverse heading can also be used.

4. Antennas should always be installed in similar height. If not possible, then measure the antenna height from the nearest deck level to antenna base and input the height to the software. This height is used to calculate the slope distance between the 2 antennas and possible pitch / roll effect. Height from CRP is not required to input in the antenna.

5. A deviation of +/- 0.2° has been recorded during marine trial of the GPS Gyro which is very much within acceptable limit of normal marine operation other than multibeam survey.

6. The heading may vary more than what is stated in para 5 above depending on the PDOP value due to non-availability of satellite.

7. Tight turns of 30°/minute and more will make the heading unstable, but it will follow a general path and will not deviate more than 2°/3°. It takes about 30 seconds for the antenna and heading to stabilize and output correct heading.

8. It is highly recommended to turn and orientate both the antennas in the same direction. See the diagram below.

Antenna Phase Centre

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Orientate this notch of both the antennas in the same general direction

001_2010 GPS Gyro SPS-461

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