USER GUIDE OCTANS III NAVIGATION & POSITIONING II. PART 2 : OCTANS III SURFACE USER GUIDE
TABLE OF CONTENTS II.1 OCTANS Technical description... II-5 II.1.1 Performances... II-6 II.1.1.1 Gyrocompass Technical Performances... II-6 II.1.1.2 Motion Sensor Technical Performance... II-6 II.1.2 Environment... II-6 II.1.3 Interface... II-7 II.1.3.1 Dimensions... II-7 II.1.3.2 Power Requirement... II-7 II.1.3.3 Outputs... II-7 II.1.3.4 Inputs... II-7 II.1.3.5 Repeater Software... II-7 II.1.4 Certification... II-8 II.2 II.2.1 II.2.2 II.2.3 MECHANICAL INTERFACE... II-9 OCTANS III Interface Plate... II-9 OCTANS III reference frame... II-11 OCTANS III center of measurements... II-12 II.3 ELECTRICAL INTERFACE... II-13 II.3.1 Description of the rear panel... II-13 II.3.2 Listing of interfaces... II-13 II.3.3 Power supply connector... II-14 II.3.3.1 Description of connector... II-14 II.3.3.2 Operational consideration... II-14 II.3.4 Repeater and configuration connector... II-15 II.3.4.1 Connection between OCTANS and PC through the repeater connector... II-15 II.3.4.2 Specifications for communication between OCTANS and PC... II-16 II.3.5 Analog Connector... II-17 II.3.5.1 Connector pin out... II-17 II.3.5.2 Analogue outputs (Pins E, F, G, H, R, S, T and U)... II-17 Part 2 : OCTANS III SURFACE USER GUIDE Page II-3
II.3.6 Digital Connector... II-18 II.3.6.1 Digital connector pin out... II-18 II.3.6.2 Serial Inputs and Outputs... II-19 II.3.6.2.1 Description... II-19 II.3.6.2.2 Pinout for electrical level RS 232 or 422... II-19 II.3.6.3 Alternative configuration and repeater port (pins K, L, d, e)... II-20 II.3.6.4 Pulses Inputs and Outputs... II-20 II.4 OPERATIONAL CONSIDERATIONS... II-21 II.4.1 Heading error due to the speed log... II-21 II.4.2 Inaccurate latitude data... II-22 II.4.2.1 Amplitude of error due to latitude data... II-22 II.4.2.2 Sensitivity to incorrect latitude data... II-22 II.4.3 Latitude input at first powering-on... II-23 II.5 COMPUTATION OF HEAVE, SURGE, AND SWAY... II-24 II.5.1 Definition of heave, surge, and sway... II-24 II.5.2 Description of the heave filter... II-24 II.5.3 Conventions for heave, surge and sway measurements... II-24 II.5.4 Monitoring external points... II-25 II.5.4.1 Principle... II-25 II.5.4.2 Definition of Lever Arms... II-26 II.5.4.3 Effect of a lever arm on the computation of heave... II-26 II.6 TRUE HEADING, ROLL AND PITCH... II-28 II.6.1 True heading... II-28 II.6.2 Roll... II-29 II.6.3 Definition of pitch... II-29 II.6.4 Angular bias compensation... II-30 II.6.4.1 Roll misalignment bias... II-31 II.6.4.2 Pitch misalignment bias... II-31 II.6.4.3 Heading misalignment bias... II-32 Part 2 : OCTANS III SURFACE USER GUIDE Page II-4
II.1 OCTANS TECHNICAL DESCRIPTION OCTANS is both a fibre-optic survey-grade IMO-certified gyrocompass and a Motion Reference Unit for marine applications. OCTANS provides true-heading, roll, pitch, yaw, heave, surge, sway, rates of turn and accelerations even in highly volatile environments. OCTANS is also certified to meet the requirements of the International Maritime Organisation (IMO) for gyrocompasses. The core of OCTANS is a compact strapdown Inertial Measurement Unit (IMU), which contains three accelerometers, three fibre optic gyroscopes, and a real-time computer (see Figure II-1). OCTANS III mechanical and electrical interfaces are fully compatible with previous OCTANS versions. Figure II-1 : The open OCTANS unit (Surface Model) The unit s computer is a Digital Signal Processor (DSP) chip enabling complex real-time computation. The heading search algorithm has been designed by ixsea. Heading and attitudes are computed whether the system is in movement or not, and without an external reference point. Computation is based on (filtered) measurement of shifts in local gravity as the Earth rotates. It involves angle integration using quaternion algebra, a heading search algorithm, and Coriolis force correction for vessel speed. Part 2 : OCTANS III SURFACE USER GUIDE Page II-5
II.1.1 II.1.1.1 PERFORMANCES GYROCOMPASS TECHNICAL PERFORMANCES Dynamic accuracy (whatever sea-state) Settle point error Settling time (static conditions) Settling time at sea : Repeatability ± 0.2 Secant Latitude (*) or 0.1 Rms ± 0.1 Secant Latitude or 0.05 Rms 1 Minute 3 Minutes Resolution 0.01 ± 0.025 Secant Latitude No Latitude limitation No speed limitation (*) Secant Latitude = 1/cosine Latitude II.1.1.2 MOTION SENSOR TECHNICAL PERFORMANCE Heave, Surge & Sway : Accuracy Resolution Heave motion periods 5 cm or 5% (whichever is highest) 1 cm 0.03 to 40 s (self adaptive) Roll, Pitch & Yaw : Accuracy 0.01 Range No limitation Follow-up speed Up to 500 /s II.1.2 ENVIRONMENT Operating temperature : Storage temperature : Shocks : Vibrations : MTBF -40 C to +60 C -40 C to +80 C 30 g in 6 ms (operating) 50 g in 11 ms (survival) 1 g sine (5 to 50 Hz) 30 000 Hours Part 2 : OCTANS III SURFACE USER GUIDE Page II-6
OCTANS III is also available in underwater housings depth-rated to 3000 meters (OCTANS 3000) and 6000 meters (OCTANS 6000). II.1.3 II.1.3.1 INTERFACE DIMENSIONS Shape : Rectangular box, splash proof(ip 66) Dimensions (L x W x H, in mm) : 276 x 136 x 148.5 Weight in air : Material : 4.3 kg Aluminium II.1.3.2 POWER REQUIREMENT Input voltage : 20 to 30 V d.c. (24 V nominal) Power consumption : 12 W (max.) II.1.3.3 OUTPUTS Serial : 3 independent and configurable digital outputs To be selected from a complete set of existing protocols(refer to Part 4 of OCTANS User Guide), with RS 232 or RS 422 levels Analog : 4 independent and configurable analogue outputs, 14 bits / ±10V Pulses : 2 pulse outputs Update rate: up to 100 Hz II.1.3.4 INPUTS Serial : 3 independent and configurable digital inputs Pulses : 2 pulse inputs Update rate : up to 100 Hz II.1.3.5 REPEATER SOFTWARE OCTANS is delivered with a powerful and easy-to-use Installation and Repeater software, which allows a complete configuration (choice of baud-rates and frequencies, data frame protocols, scale factors for analogue I/O, multiple lever arms, filtering parameters.). Refer to Part 3 of the OCTANS User Guide for a full description of the software. Part 2 : OCTANS III SURFACE USER GUIDE Page II-7
II.1.4 CERTIFICATION OCTANS complies with the regulations of the International Maritime Organisation resolutions A.424 (XI), A. 694 (17), A.183 (19) for gyrocompasses, with SOLAS 74 as amended (regulations V/12 (d), (i)) and IEC 60945, IEC 61162-1 and ISO 8728. OCTANS surface has been awarded certificate N 09807/A0 EC from certifying authority N 0062. A copy of all relevant documentation is available upon request to IXSEA. Part 2 : OCTANS III SURFACE USER GUIDE Page II-8
II.2 MECHANICAL INTERFACE II.2.1 OCTANS III INTERFACE PLATE OCTANS is installed using three M6 screws accessible from the top of the unit (see Figure II-2). Alignment is carried out by means of two centering pins, enabling relatively precise point/line positioning, located on the bottom plate of the OCTANS (accuracy of positioning is ±0.04 degree). These pins are located on the OCTANS centerline, as shown by grooves on the front and rear of the gyrocompass. The mechanical tolerance in the manufacture of OCTANS bottom plate allows to have 0,01 of accuracy on the centerline of the unit. IMPORTANT : The rear panel of OCTANS is default defined as the one with the connectors. Part 2 : OCTANS III SURFACE USER GUIDE Page II-9
Figure II-2 : OCTANS mounting diagram Part 2 : OCTANS III SURFACE USER GUIDE Page II-10
II.2.2 OCTANS III REFERENCE FRAME All inertial measurements are default performed in OCTANS reference frame (X1, X2, X3). This frame is defined in Figure II-3. X 3 X 2 X 1 X 2 Figure II-3 : definition of OCTANS III reference axes X 1, X 2 and X 3 Part 2 : OCTANS III SURFACE USER GUIDE Page II-11
II.2.3 OCTANS III CENTER OF MEASUREMENTS Motion sensing measurements are default measured at OCTANS III center of measurements, which is defined in Figure II-4. Measurements can be performed at an external monitoring point. The position of this point has to be measured with respect to OCTANS III center of measurement and entered in the OCTANS Configuration through the Installation and Repeater Software. Details on external points monitoring is given in section II.5.4. Figure II-4 : position of OCTANS III center of measurements Part 2 : OCTANS III SURFACE USER GUIDE Page II-12
II.3 ELECTRICAL INTERFACE II.3.1 DESCRIPTION OF THE REAR PANEL All OCTANS inputs/outputs are made via four sealed connectors, SOURIAU 851 plug type. The rear panel of the OCTANS unit holding these connectors is shown in Figure II-5. The connector references are as follows: Power supply: Repeater: Analogue I/O: Souriau 851 02 E 8 33 P 50 16 - Ni Souriau 851 02 E 12 10 P 50 16 - Ni Souriau 851 02 E 14 19 P 50 16 - Ni Serial & pulses I/O : Souriau 851 02 E 20 41 P 50 16 Ni Figure II-5 : OCTANS rear panel II.3.2 LISTING OF INTERFACES OCTANS is fitted with 4 connectors configured to provide the following: Power supply, described in II.3.3, Repeater and configuration port (only RS232 level), described in II.3.4, 4 analogue Outputs described in II.3.5.2, 3 Serial Inputs RS232/422 user-configurable, described in II.3.6.2.2, 3 Serial Outputs RS232/422 user-configurable, described in II.3.6.2.2, 2 pulse Inputs described in II.3.6.4, 2 pulse Outputs described in II.3.6.4. These interfaces can be user configured. This is done with the Installation and Repeater Software installed on a PC connected to OCTANS. Please refer to the Part 3 of the OCTANS User Guide for details. Part 2 : OCTANS III SURFACE USER GUIDE Page II-13
II.3.3 II.3.3.1 POWER SUPPLY CONNECTOR DESCRIPTION OF CONNECTOR OCTANS is powered with a standard 24 V DC supply. It is possible however to supply power with any voltage between 20 V and 30 V. Maximal power consumption is 12 W in all cases. OCTANS does not possess an on/off switch. As soon as it is powered, it begins to seek geographical North. 24 VDC A Mechanical C B Ground OCTANS can be powered by 2 methods: Via the AC/DC converter provided with the local standard power supply. It is not recommended to use this converter to power OCTANS from another source of power than the country mains. In particular, it is not recommended to use this converter onboard a vessel. Via a 3-wire cable for direct connection to a 24 V power supply. The special cable that is provided with the OCTANS is either black or grey. Wiring is detailed on Table II-1. Pin A 24 V DC (20 V to 30 V) B GROUND C Mechanical ground Signal Table II-1 : Configuration of power supply cable provided by IXSEA II.3.3.2 OPERATIONAL CONSIDERATION IMPORTANT : any interruption of the power supply, even brief, will return the system to its initial condition and it will begin to seek North again. The alignment phase will start over. OCTANS will operate with a DC voltage between 20 V and 30 V. Part 2 : OCTANS III SURFACE USER GUIDE Page II-14
II.3.4 REPEATER AND CONFIGURATION CONNECTOR This connector is used for configuring OCTANS and / or to display data throughout the repeater software. Please refer to Part 3 of the OCTANS User Guide for details on the software. OCTANS is delivered with a cable for a direct connection to a PC. Mechanical Ground A B L M N P C K V R U J T H G S D E F II.3.4.1 CONNECTION BETWEEN OCTANS AND PC THROUGH THE REPEATER CONNECTOR Connection between OCTANS and PC through the Installation and Repeater connector is made using the dedicated cable delivered with the unit : Connector reference FCI 851 06 J1210 S50 Ni at one end to be plugged into OCTANS Installation and Repeater connector at one end SUB D9 connector at the other end to be plugged into any PC serial port. The following table describes the connection between the OCTANS Repeater connector pins and the SUB D9 connector. OCTANS Repeater connector PC SUB D9 connector Pin Signal Pin Signal A ConfigOUT GND 5 PC GND B ConfigOUT + 2 PC Rx D ConfigIN GND 5 PC GND E ConfigIN - 5 PC GND F ConfigIN + 3 PC Tx J Mechanical GND Communication cable between OCTANS and PC through the Repeater connector Note : pins A, D and E need to be connected to Pin 5 of DB9 for the communication to work properly. Part 2 : OCTANS III SURFACE USER GUIDE Page II-15
II.3.4.2 SPECIFICATIONS FOR COMMUNICATION BETWEEN OCTANS AND PC OCTANS can be connected to a PC for configuration, installation and display purposes. The I/O signal is available either through the Installation and Repeater connector (see section II.3.4.1) or through the Digital I/O connector (see section II.3.6). Whatever the way for connecting OCTANS to PC, data flows in and out in RS 232 format with the following characteristics : protocole used : OCTANS Standard (see the OCTANS library documentation for a description of OCTANS Standard data frame output) Baudrate : 19.2 kbauds Flow Control : Odd, 2 stop bits Refresh rate : 5 Hz (200 ms) Warning : It is not possible to connect OCTANS to PC from both the Repeater and the Digital connector. This could lead to communication errors between OCTANS and PC. Part 2 : OCTANS III SURFACE USER GUIDE Page II-16
II.3.5 II.3.5.1 ANALOG CONNECTOR CONNECTOR PIN OUT Pin Signal Pin Signal A AnaInAGnd L AnaInBGnd B AnaInASig M AnaInBSig C Reserved N Reserved D Reserved P Reserved E AnaOutASig R AnaOutAGnd F AnaOutBSig S AnaOutBGnd G AnaOutCSig T AnaOutCGnd H AnaOutDSig U AnaOutDGnd J Mechanical Ground V Reserved K Reserved Table II-2 : Configuration of the analog I/O connector II.3.5.2 ANALOGUE OUTPUTS (PINS E, F, G, H, R, S, T AND U) Four ±10 V outputs are available on OCTANS. These outputs offer 14-bit resolution at 100 Hz and are identified by the signals AnaOut_Gnd and AnaOut_Sig. Analog Output A uses pins E (AnaOutASig) and R (AnaOutAGnd), Analog Output B uses pins F (AnaOutBSig) and S (AnaOutBGnd), Analog Output C uses pins G (AnaOutCSig) and T (AnaOutCGnd), Analog Output D uses pins H (AnaOutDSig) and U (AnaOutDGnd). The analog outputs can be user configured (signal and scale factor). For more details on configuration, please refer to the Part 3 of the OCTANS III user guide. A female connector is available to directly connect the wires. Part 2 : OCTANS III SURFACE USER GUIDE Page II-17
II.3.6 II.3.6.1 DIGITAL CONNECTOR DIGITAL CONNECTOR PIN OUT Pin Signal Pin Signal A SerOutAGnd Y SerInAV+ B SerOutAV+/232 Z SerInBV- C SerOutAV- a SerInBV+ D SerOutBGnd b SerInCV- E SerOutBV+/232 c SerInCV+ F SerOutBV- d ConfigREPin- G SerOutCGnd e ConfigREPIn+ H SerOutCV+/232 f ConfigREPInShield J SerOutCV- g NumInBV- K ConfigOutGnd REP h NumInBV+ Mechanical Ground W A V X U j T i k s S h t r R g q P f e N M L B C Y D Z E m a F n p b G c H d J K L ConfigOutREP V+ i NumInAV- M Reserved j NumInAV+ N Mechanical Ground k ConfigInAShield P Reserved m ConfigInBShield R Reserved n ConfigInCShield S Reserved p Reserved T NumOutBGnd q Reserved U NumOutBSig r NumInAShield V NumOutAGnd s NumInBShield W NumOutASig t Reserved X SerInAV- Table II-3 : Configuration of the Digital connector Part 2 : OCTANS III SURFACE USER GUIDE Page II-18
II.3.6.2 SERIAL INPUTS AND OUTPUTS II.3.6.2.1 Description Three serial inputs and three serial outputs are available, which can be entirely configured. For more details, please refer to Part 3 of the OCTANS III user guide. For each I/O, configuration parameters include : Electrical levels : RS 232 or 422 (see detailed pin out hereafter), Pair, parity: No parity, Even parity or Odd Parity, Number of bits: 0.5, 1, 1.5, or 2 stop bits, Data transmission rate: from 600 Bauds to 115.2k Protocol: protocols based on NMEA 0183, ASCII or Binary, Output frequency: 0.1 Hz to 100 Hz. II.3.6.2.2 Pinout for electrical level RS 232 or 422 The pins that are used for RS 232 I/O configuration are given in the following table: OutGnd Out /+ 232 InGnd In /+232 InShield (option) A SerOutAGnd (A) SerOutAV+/232 (B) SerInA V- (X) SerInA V+ (Y) ConfigInAShield (k) B SerOutBGnd (D) SerOutBV+/232 (E) SerInBV- (Z) SerInBV+ (a) ConfigInBShield (m) C SerOutCGnd (G) SerOutCV+/232 (H) SerInCV- (b) SerInCV+ ( c ) ConfigInCShield (n) Note 1 : All Serial Inputs are independent but it is however possible to connect the OutGnd to the InGnd to use a single SUB D9 serial connector. Note 2 : SerOutGnd is internally connected to ConfigOutGnd and AnaOutGnd The pins that are used for RS 422 I/O configuration are given in the following table: OutGnd / InGnd Out /+422 Out /-422 In /+422 In /-422 A SerOutAGnd (A) SerOutAV+/232 (B) SerOutAV- ( C ) SerInAV+ (Y) SerInAV- (X) B SerOutBGnd (D) SerOutBV+/232 (E) SerOutBV- (F) SerInBV+ (a) SerInBV- (Z) C SerOutCGnd (G) SerOutCV+/232 (H) SerOutCV- (J) SerInCV+ ( c) SerInCV- (b) Note 3 : You can also use the Shield Pins k, m and n for I/O A, B or C respectively. Part 2 : OCTANS III SURFACE USER GUIDE Page II-19
II.3.6.3 ALTERNATIVE CONFIGURATION AND REPEATER PORT (PINS K, L, D, E) This option can be used by following the pin out shown in the following table. Repeater or configuration I/O OutGnd Out /+232 InGnd In /+232 ConfigOutGnd (K) ConfigOutV+ (L) ConfigREPIn- (d) ConfigREPIn+ (e) Note: This port can ONLY be used for Repeater or configuration purpose. You can also add pin f (ConfigREPInShield) for shielding. II.3.6.4 PULSES INPUTS AND OUTPUTS Two inputs and two outputs of on/off type are available. These pulse I/O are identified by the signals NumIn_Gnd, NumIn_Sig, NumOut_Gnd, NumOut_Sig and optionally NumInShield (pins T, U, V, W, g, h, i, j, r and s) and allow connection and simulation of pulse speed logs. In particular, the scale factor (number of pulses per knot) can be configured. Part 2 : OCTANS III SURFACE USER GUIDE Page II-20
II.4 OPERATIONAL CONSIDERATIONS All gyrocompasses, OCTANS included, are sensitive to the speed of the vessel and to the current latitude. However these errors are small. Latitude needs to be updated into OCTANS only if the ship changes latitude very substantially, and very precise speed measurement is not imperative. II.4.1 HEADING ERROR DUE TO THE SPEED LOG The heading output of all gyrocompasses is sensitive to the speed of travel of the vessel towards North. The international standard (ISO 8728) defines that: Course error in degrees for a gyrocompass aligned north-south is determined by the formula V/5π x the secant of the latitude, where V is the North component of the speed in knots. This speed correction applies whatever the technology used for the gyroscopes. Indeed, the linear speed of a boat travelling on the terrestrial sphere produces, with respect to the Earth and therefore with respect to the inertial frame of reference, a rotational speed V/R, where R is the radius of the Earth. This rotation speed (Coriolis force) has an influence on the measurement of the speed of rotation of the Earth and therefore on the detection of North. Using the above formula, it is easy to compute the maximum speed V North max for which the heading error due to speed is higher than the heading accuracy specification. OCTANS dynamic accuracy is ±0.2 degree x secant of latitude and therefore we have : V North max = 0.2 x 5π 3,2 knots. Even though this is a relatively low value, it is recommended to enter the speed into OCTANS for automatic compensation of speed error and full accuracy performances of the gyrocompass. Vessel speed can be input either manually or through an external Log sensor (see Part 3 of OCTANS User Guide for details on OCTANS configuration). When entered manually, a few knots accuracy on speed is satisfactory. Speed input from an external sensor (GPS or Log sensor) allows real-time update of the vessel speed. Part 2 : OCTANS III SURFACE USER GUIDE Page II-21
II.4.2 II.4.2.1 INACCURATE LATITUDE DATA AMPLITUDE OF ERROR DUE TO LATITUDE DATA Gyrocompasses are intrinsically sensitive to latitude. Heading error depends on the secant of the latitude as a general physical rule : heading cannot be defined at the geographical poles. System However, it is not this error which is considered here, but rather intrinsic system inaccuracy when it has unreliable data for the latitude of the current location. OCTANS has to know the latitude of its location in order to find geographical North rapidly. If the latitude information input is incorrect, OCTANS will produce an error. This error is nevertheless very small: The curve in Figure II-6 shows the heading error in degrees multiplied by the secant of the latitude versus the latitude of the current location, assuming that the latitude entered in OCTANS is incorrect by one degree. 0,05 0,04 Error in degrees 0,03 0,02 0,01 0-0,01-0,02-0,03 0 10 20 30 40 50 60 70 80 90 Latitude in degrees Figure II-6 : Heading error in degrees by secant of latitude (for a 1 degree latitude error) Example: at 40 latitude, an error of 3 in the latitude will cause 3x0,02 = 0,06 sec. Lat error on heading II.4.2.2 SENSITIVITY TO INCORRECT LATITUDE DATA In practice, OCTANS needs to know the latitude only to an accuracy of 3 degrees at 45 degrees latitude. This dependency is more important at low latitudes. It is recommended to enter the current latitude in the system with 1 accuracy for latitudes below 30 degrees. Latitude can be updated into OCTANS during operation, either manually or by connecting an external GPS as an input. Refer to Part 3 of the OCTANS III User Guide for details. Part 2 : OCTANS III SURFACE USER GUIDE Page II-22
II.4.3 LATITUDE INPUT AT FIRST POWERING-ON OCTANS is delivered with a default latitude setting which corresponds to IXSEA s factory location. At first powering-on, OCTANS will start seeking north with this latitude input, which may be quite different from the current OCTANS latitude. Latitude has to be modified by the user (refer to Part 3 of OCTANS III User Guide). Once this modification is performed, it is recommended to save the current latitude into OCTANS PROM and re-start the OCTANS. This procedure allows for the OCTANS to enter the correct latitude value as an input in the North finder algorithm as soon as computation starts. OCTANS will then reach full accuracy after the 5 minutes alignment phase. Otherwise, time for OCTANS stabilization will be increased due to the wrong initial latitude input when computation starts. This procedure should be done whenever a unit is delivered from factory, or whenever a new firmware has been re-loaded into the unit. Part 2 : OCTANS III SURFACE USER GUIDE Page II-23
II.5 COMPUTATION OF HEAVE, SURGE, AND SWAY II.5.1 DEFINITION OF HEAVE, SURGE, AND SWAY The heave, or vertical motion of the vessel, is determined by the double integration of the vertical acceleration. Unfortunately, the vertical acceleration is measured with small bias due to the physical limitations of the sensors. Because of this bias component, the double integration, which represents vertical position, can diverge to infinity very quickly. The best solution, used in every motion sensor, is to use a highpass filter, which nulls out the bias component effect. By definition, the vertical amplitude of a movement which is filtered to cut-off the frequency around zero, is called "Heave". Respectively, the two horizontal positions filtered to cut-off the frequency around zero, the surge and the sway. II.5.2 DESCRIPTION OF THE HEAVE FILTER Since the heave (surge and sway) output is high-pass filtered, the output will always return to zero when OCTANS is static. The heave filter has been fully redesigned in OCTANS III, and is now automatically configured in terms of time constant : there is no need for the user to input any parameter. Heave filter is initialized each time OCTANS is re-started. The duration of the heave initialization phase is roughly 5 minutes, and follows the 5 mn OCTANS alignment phase. Hence, heave, surge and sway deliver accurate value after a total initialization phase shorter than 10 minutes. Once the heave filter has been automatically initialized, it will respond to variations of OCTANS positions in the three directions (heave, surge and sway) defined in section II.5.3. After experiencing a step change in vertical position, OCTANS heave output will gradually return to zero within 1 to 2 minutes. If OCTANS is moved following a sine or a combination of sinus, as usually observed with swell movements, the heave (surge and sway) output will follow this movement, for swell periods up to 40 seconds. OCTANS III heave filter has been sea-proven. A copy of the test report may be sent to you on demand, please contact ixsea Customer Support (inertial.support@ixsea.com). II.5.3 CONVENTIONS FOR HEAVE, SURGE AND SWAY MEASUREMENTS The axis directions for heave surge and sway measurements are the directions of the three OCTANS reference axes X3, X1 and X2 respectively (see Figure II-3). The heave is default defined positive up along OCTANS vertical axis X3. Part 2 : OCTANS III SURFACE USER GUIDE Page II-24
The surge is default defined positive on a horizontal axis pointing to the direction opposite of the connectors (axis X1). The sway is default defined positive on a horizontal axis pointing to the left of OCTANS (on the port side of the boat, if OCTANS is correctly mounted), along X2. II.5.4 MONITORING EXTERNAL POINTS All measurements are referenced to the convergence centre of sensors axis. This reference point is shown in Figure II-4. All installation offsets shall be considered respective to this point. II.5.4.1 PRINCIPLE OCTANS is able to calculate the motion of several external monitoring points. Effective from firmware 4.1, one primary and three secondary monitoring points are available. For each one of those external monitoring points, data can be output with a completely different setting including serial or analogue I/O. In particular, at each location, a different protocol can be set. This allows, for instance, to drive a multibeam on one side of a vessel, to drive a single beam echo sounder at another location, to send analogue heave info to a sub-bottom profiler (see for an illustration). Secondary Lever Arm #1, output 1 Primary Lever Arm Secondary Lever Arm #2, output 2 Figure II-7 : monitoring different points with OCTANS III Part 2 : OCTANS III SURFACE USER GUIDE Page II-25
II.5.4.2 DEFINITION OF LEVER ARMS External monitoring point are defined by their Lever Arm to OCTANS III center of measurement. This lever arm is the triplet of cartesian coordinates (LV1, LV2, LV3) defining the position of external monitoring point M with respect to OCTANS center of measurements in the OCTANS reference frame (X1, X2, X3) see Figure II-8. External Monitoring point LV 3 X 1 LV 1 X 3 OCTANS center of measurements X 2 LV 2 Figure II-8 : definition of lever arm II.5.4.3 EFFECT OF A LEVER ARM ON THE COMPUTATION OF HEAVE OCTANS can be located anywhere from the monitoring point. The heave measured at the monitoring point can be very different from the one measured at OCTANS center of measurement, due to the lever arms. Figure II-9 illustrates a setting where OCTANS monitors an external point located ahead along the X1 axis. The heave of OCTANS is null, however the heave at the monitoring point is not null when pitch angles are experienced. Horizontal plane OCTANS center of measurement (null heave) Pitch External Monitoring Point Non zero heave Figure II-9 : Effect of lever arms Part 2 : OCTANS III SURFACE USER GUIDE Page II-26
To avoid this effect, it is recommended to locate OCTANS as close as possible to the monitoring point. Otherwise, it is possible to compensate for the effects of lever arms by computation. Lever arms can be configured into OCTANS for up to four external monitoring points (refer to Part 3 of the OCTANS User Guide). Part 2 : OCTANS III SURFACE USER GUIDE Page II-27
II.6 TRUE HEADING, ROLL AND PITCH Roll, pitch and heading are the three Euler angles which transform the local geographic frame into the OCTANS reference frame. The local geographic frame is defined with the three axes ( see Figure II-10) : - X N, which lies in the horizontal plane, pointing towards geographical North, - X W, which lies in the horizontal plane, pointing towards West, - X up, parallel to the local vertical, pointing up. North pole X N X up X W OCTANS reference frame is defined on Figure II-3. Figure II-10 : definition of the local geographic frame II.6.1 TRUE HEADING The true heading is the angle between the vertical plane oriented in the North direction and the vertical plane passing through OCTANS. Heading is counted positive from North, varying from 0 to 360 degrees. The orientation of this angle is given in Figure II-11, in case of null pitch and roll. X N Heading X 1 X up // X 3 X 2 + X W Figure II-11 : Definition of true heading Part 2 : OCTANS III SURFACE USER GUIDE Page II-28
II.6.2 ROLL Roll is defined as the angle of rotation performed around OCTANS axis X1 so that OCTANS axis X2 lies in the local horizontal plane. For small pitch values, the roll is the angle between the horizontal plane and the axis 2 of OCTANS. This angle is default defined positive in the direction of axis 1, i.e. when the boat s port side is up. Figure II-12 is an illustration of the roll angle with null pitch. + X up X 3 X N // X 1 X2 X 2 Roll X W Figure II-12 : Definition of roll II.6.3 DEFINITION OF PITCH The pitch is the angle between the axis X1 of OCTANS and its projection in the local horizontal plane. This angle is default defined positive in the direction of axis X2, i.e. when the boat s bow is down. Figure II-13 is an illustration of pitch angle in case of null roll. X up X 3 X W // X 2 + X N Pitch X 1 Figure II-13 : Definition of pitch Part 2 : OCTANS III SURFACE USER GUIDE Page II-29
II.6.4 ANGULAR BIAS COMPENSATION OCTANS can be installed with any orientation with respect to the vessel. OCTANS measures heading and attitude with respect to its reference frame defined by the 3 veaxes X1, X2 and X3 (see Figure II-3). OCTANS reference frame may not be parallel to the vessel reference frame. Heading and attitude outputs can be compensated for angular misalignments of OCTANS relative to the vessel reference frame so that OCTANS outputs heading and attitude of the vessel. This is done by setting misalignment bias for the three reference axis. These bias are the Euler angles which relate OCTANS and vessel reference frame. Pour cela, des biais de cap, roulis et tangage peuvent être configurés dans le logiciel OCTANS. Vessel reference frame is depicted on Figure II-14. OCTANS reference frame is depicted on Figure II-3. XV3 XV1 XV2 Figure II-14 : vessel reference frame Configuring angular misalignment bias into OCTANS is performed through the Installation and Repeater software (refer to Part 3 of the OCTANS User Guide). The definition of the angular misalignment bias is given in the following sections, for pure roll (respectively pitch and heading) misalignment. These definitions are still valid when the misalignment between OCTANS and vessel frames is a combination of misalgnments on the three angles, as soon as the angles remain small (order of magnitude is 1 degree). Part 2 : OCTANS III SURFACE USER GUIDE Page II-30
II.6.4.1 ROLL MISALIGNMENT BIAS The roll misalignment bias is the angle of the rotation around OCTANS axis X1 which superimpose OCTANS axis X2 with vessel axis XV2. On Figure II-15, the roll misalignment bias is negative. XV3 X 3 Roll bias X 2 XV2 Figure II-15 : roll misalignment bias II.6.4.2 PITCH MISALIGNMENT BIAS Pitch misalignment bias is the angle the angle of the rotation around OCTANS axis X2 which superimpose OCTANS axis X1 with vessel axis XV1. On Figure II-16, the pitch misalignment bias is negative. XV3 X 3 Pitch misalignment bias X 1 XV1 Figure II-16 : pitch misalignment bias Part 2 : OCTANS III SURFACE USER GUIDE Page II-31
II.6.4.3 HEADING MISALIGNMENT BIAS The heading misalignment bias is the angle of rotation around around OCTANS axis X3 which superimpose OCTANS axis X1 with vessel axis XV1. On Figure II-17, the heading misalignment bias is positive. X 1 Heading misalignment X 1 XV1 XV2 X 2 Figure II-17 : heading bias misalignment Part 2 : OCTANS III SURFACE USER GUIDE Page II-32