Astra A5022 Bedienungsanleitung

A5022 FLUXGATE COMPASS USER MANUAL

A5022 manual.doc

April 2016

Table of Contents

1 Introduction and description of fluxgate compass.

1.1 Description of compass

1.2 Connections

1.2.1 Normal

1.2.2 Variants -CP

1.3 Switches

1.4 Indicator light

1.5 Power supply.

1.6 Mounting

2 Connecting the compass to your application.

2.1 To a NMEA-0183 instrument.

2.2 To a PC serial port.

3 Output formats available from compass.

3.1 NMEA-0183

3.2 Furuno AD-10

4 Calibrating the compass.

4.1 Why the compass needs calibrating.

4.2 Starting calibration.

4.3 Aborting a bad calibration.

4.4 Setting reference NORTH heading

4.5 Set-up suggestions

5 Configuration

6 References

1. Introduction and description of fluxgate compass.

1.1 Description of compass.

The Astra Yacht NMEA compass unit is a complete component for a compass system indicating,

RADAR ‘North-up’ input or autopilot. It is housed in a water-resistant enclosure so it can be

mounted outside a steel hull. It delivers heading data in two industry-standard forms.

The A5022 contains a fluxgate with floating core surrounded by high-precision interface circuits, which,

together with the special clockwise/anticlockwise and offset nulling sequence allow a

microprocessor to acquire a binary value from two orthogonal sensors of the horizontal component

of the Earth’s magnetic field. The processor calculates the vector from these values, uses a

calibration table to correct for local field disturbance errors, offsets the result and then presents the

data in a manner which has been requested. Such requests alter the frequency of the data, the

degree of filtering and the offset value. Calibration sequences can also be commanded.

1.2 Connections

1.2.1 Normal

Conductor

Colour

Type

Function

Red

+Supply 8-30v

Yellow

Furuno AD-10 Clock

Brown

NMEA IN-

White

NMEA IN+

Black

GND

Green

NMEA OUT+

Blue

GND

Violet

Furuno AD-10 Data

Screen

NOTE Conductors 5 and 7 are connected together inside the A5022

1.2.2 Variants with suffix -CP

Conductor

Colour

Type

Function

Red

+ Supply

Yellow

NMEA IN +

Blue

GND and NMEA IN -

Green

NMEA OUT +

NOTE Cable foil and drain wire internally connected to GND

1.3 Switch Inputs

Fig 1

Except for variants with suffix -S, two push-button switches are provided for calibrating the

compass in the field.

When the A5022 is viewed from the front face with the LED facing, then Switch 1 is on the right and

Switch 2 is on the left.

1 Switch 1: Start the auto-calibration process

2 Switch 2: Set reference NORTH heading. The A5022 must be mounted upright

but at any azimuth. Pressing S2 sets the heading to zero and so can be done when the

whole installation is headed North.

3 Both together Pressing both together for at least one second causes the auto-

calibration process to halt and restores the previously saved calibration values.

1.4 Indicator light

A blue light indicates three states of the A5022.

State 1 Uncalibrated long flash

State 2 In the process of calibration continuous

State 3 Calibrated short flash

After the reset command $PATC,IIHDG,0CV<CR><LF>, the A5022 is uncalibrated and will have

a long flash.

Note that the LED can be turned off and on by the DLED command – see section 5.

1.5 Power supply

The compass is compatible with any DC power supply of between 8 and 30 Vdc. Typical supply current

during operation is approx. 25mA. The compass is protected against reversed polarity.

Note that the operation of the LED adds another 10mA and that during auto-calibration the

consumption can be as high as 60mA.

Care should be taken to make sure the compass is not situated too close to the power supply, as it’s

accuracy may be affected by either the iron in the mains transformer, or by magnetic field ‘noise’

from a switching power supply. It is not possible to cover all possible scenarios here, and it

remains up to the user to determine the suitability of a possible location for the compass.

Note that the output from the A5022 takes several seconds to stabilize after a power is applied; the time

taken depends on the damping settings. There is a command - see section 5 – which can be

used to suppress the output after power-up.

1.6 Mounting

The compass is fixed to the chassis of the vessel or vehicle in the upright position using the fixing holes

shown in the data sheet. It does not matter which way it faces as the azimuth can be set to North

at any time the chassis is orientated North. Alternatively if the azimuth of the chassis is known,

then the A5022 may be rotated before fixing to North using a protractor. S2 is then pressed and

then the compass can be mounted on the chassis.

A5022

COM PORT D

CONNECTOR

4 NMEA IN +

3 NMEA IN -

5 GND

6 NMEA OUT +

7 GND

POWER

SOURCE

-1 +8-30V

2 Connecting the compass to your application

2.1 Compass to a NMEA-0183 instrument

The hardware on which the NMEA-0183 standard is based on is a balanced serial protocol called

RS422. This means that two wires are need for send and two for receive.

Fig 2

Note that the GND wire is used for the current return path. This might be shared with the

NMEA- wire in some installations.

2.2 Compass to a PC serial port

In many cases the wires can be joined directly as shown in Fig 2. Alternatively use the Astra

Yacht A3036 serial interface unit.

Fig 3

External NMEA device

6 NMEA OUT +

4 NMEA IN+

3 NMEA IN-

5 GND

NMEA current

source

3 Output formats available from compass

3.1 NMEA-0183

The serial output format is: 4800 Baud, 8 data bits, 1 stop bit, no parity.

The compass sends information using the standard NMEA-0183 sentence ‘HDG’: Magnetic

Heading, Deviation, and Variation. But note that the information of Deviation and Variation is

not sent and so blank fields are defined by consecutive commas. In the A5022 the sentence

may have one of several forms typically of the general form:

$HCHDG,hhh.h etc

Where hhh.h is the magnetic heading from 000.0 to 359.9 degrees

Also the Rate-of-turn data is sent either with or without the heading sentence.

For a complete list of output formats available see Section 5

3.2 Furuno AD-10

The compass has a separate, dedicated output in Furuno AD-10 format. This is a proprietary

4 character serial format, which gives heading in degrees and tens of minutes. The string

0872 represents the heading 87° 20’ so that the precision is to 1/6 of a degree. At the

same time the A5022 would be also sending the NMEA data to a precision of 1/10 of a

degree.

480µs

100ms minimum

Duration of data is 16 clocks each

high=low=30µs. Total = 480µs.

Frequency of data packets is set by

the interval command. Max = 10Hz

Clock

Data

Fig 4

4 Calibration

4.1 Why the compass needs calibrating

When any compass is installed the magnetic characteristics of the whole installation affect the

way the Earth’s field reaches the detector inside the device. Each individual installation

will be different and so the A5022 is equipped with an auto-calibration routine which

corrects for these installation distortions.

4.2 Starting calibration

-A NMEA-0183 command can be sent to initiate the process.

-Switch 1 can be pressed to start it.

There are two compass calibration techniques in common use:

1 Constant angular velocity

2 Double rotation without constant velocity.

The A5022 uses the first method. The process consists of rotating the whole installation in the

Earth’s field so that both permanent magnets and induced magnets are corrected. The

method used is the single turn at a constant rate and this rate should be in range 60 to

180 seconds for the full 400 degrees needed. The whole arrangement is turned at

constant angular velocity because the method relies on applying a correction when the

heading measured is uneven with time.

The second method is not used in the A5022. Astra Yacht has evaluated the method which

uses a mathematical model of an ideal compass and treats errors as arising from

distortion due to magnetic objects. The ideal error plot of the field vector would be a circle

with no offset from the origin. Permanent magnets (‘hard’) have the effect of shifting the

centre from the origin and induced magnets (‘soft’) modify the circle into an ellipse. The

results of our investigation show that there is always a residual error due to the fact that

real magnetic objects do not behave exactly according to the model outlined. Astra Yacht

is aware that the need for a constant angular velocity is onerous but the benefit is that it

provides a very low residual error – less than 0.5°.

Note that the calibration is different if the unit is mounted upside-down.

Calibration must always be done with the unit in its final mounted position. The essential point

of the calibration is remove the influence of external magnetic components in the vicinity

– the nearby pieces of iron and steel –so it is essential that these remain unchanged after

calibration. If any significant iron component is altered – such as the installation of new

equipment or replacement of equipment such as winches or engines – then the

calibration must be re-done.

4.3 Terminating a bad calibration

If the process is faulty in any way – such as would happen if the manoeuvre cannot be

completed, the process can be terminated by the NMEA command listed and the original

factory default (linear) table is restored. Alternatively this can be done by pressing both

Switches together for at least 1 second.

NOTE that there should be a delay of at least 5 seconds after termination before a new

calibration process is initiated.

4.4 Setting reference NORTH heading

Switch 2 (and also a NMEA command) is provided to set ‘zero’. The A5022 should

a. first be auto-calibrated

b. then be aligned to North

4.5 Set-up suggestions

When the A5022 is fixed in place and connected it can be calibrated as described above.

Choose a calm day and a region of water where there are no currents. Set the boat

turning to left or right at a slow rate and fix the wheel or tiller. Then, when the turning is

steadily under way, press the auto-calibrate button and watch the LED.

When calibration is completed the boat can be on its way and the next task is to set North.

This is best done by identifying transits on a chart and heading the boat on the transit.

Again this should be done in the same conditions so that the heading can be lined up on

the transit and maintained while the set-zero button is pressed.

5 NMEA-0183 inputs

The compass can be configured by sending various proprietary sentences to its NMEA-0183

input. Once configured, the compass will remember those settings every time it is

powered up.

Response:

When any of the following input sentences are received the A5022 will reply with an

‘acknowledge’ output sentence of the format:

$PATC,HCHDG,ACK<CR><LF>

5.1 Start Auto-Calibration

$PATC,IIHDG,IAC<CR><LF>

Refer to section 4.2. Same as pressing Switch 1 – see 4.4.

5.2 Abort Auto-Calibration.

$PATC,IIHDG,XCL<CR><LF>

Refer to section 1.3.

5.3 Resets all compass data to factory default values:

$PATC,IIHDG,0CV<CR><LF>

Output rate u= 100 milliseconds (10 updates/second),

output damping d= 50 percent

heading offset f= 0 degrees.

5.4 Set heading:

$PATC,IIHDG,AHD,fff.f<CR><LF>

Forces the heading to a certain value by supplying an offset which is stored and used

thereafter.

Where f is in degrees with a valid range of 000.0 to 359.9

When f = 000.0 the result is the same as pressing switch 2 – see 1.3.

5.5 Set the Output update period:

$PATC,IIHDG,TXP,uuuu<CR><LF>

Valid range is u=100 to 3000 milliseconds. This is limited by max. data rate of NMEA-0183

output at 4800 baud.

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