Ocean_Surveyor_Installation_Guide_PN_95A-6019-00_April_2014.pdf

Ocean Surveyor / Ocean Observer

INSTALLATION GUIDE

P/N 95A-6019-00 (April 2014)

© 2014 Teledyne RD Instruments, Inc. All rights reserved.

P/N 95A-6019-00 (April 2014)

© 2014 Teledyne RD Instruments, Inc. All rights reserved.

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TABLE OF CONTENTS

CHAPTER 1 - AT A GLANCE

Introduction How to Contact Teledyne RD Instruments Ocean Surveyor/Observer Overview

Power Considerations Computer Considerations Electronics Chassis Considerations Cabling Considerations I/O Cable Identification Navigation Interface Considerations Using Trigger-In and Trigger-Out

Installation Overview Alignment Overview

CHAPTER 2 – TRANSDUCER INSTALLATION

Transducer Mounting Considerations

Location Orientation

Other Considerations Floating Objects Acoustic Window Sea Chest Fairing Air Bubbles Flow Noise Corrosion and Cathodic Disbondment Ringing Acoustic Isolation Maintenance

CHAPTER 3 - USING ACOUSTIC WINDOWS

Acoustic Window Overview

Background - Should I use an Acoustic Window?

Advantages Disadvantages

What Window should I use?

Are there any Other Windows that I can consider?

Acoustic Window Installation What should the Window Shape be?

Can I Add Strengthening to the Window?

How do I Secure the Window to the Well Opening?

How to Prevent the Window from Cracking When Going Into Dry Dock?

How Much Space should I Have between the Window and Transducer?

What Other Issues should be Considered When Using an Acoustic Window?

What Fluid Should I Fill the Sea Chest With?

How Much Fluid Should I Use in the Sea Chest?

Should I Use Absorption Material When Using a Window?

Do I Need to Worry About Corrosion When Using a Window?

Do I Need to Worry About Air Bubbles When Using a Window?

Do windows Improve Flow Noise Problems?

What Maintenance is required when using Windows?

How Often Should I Inspect the Window?

If I find that the Window is Damaged Can I Keep Operating the ADCP?

Does the Use of a Window Effect My Warranty?

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Insertion Loss Conceptual Transducer Well Design

CHAPTER 4 - GYROCOMPASS INTERFACE

Gyrocompass Interface Considerations Overview of the ADCP Gyro Interface

Determining the Synchro Stator Voltage Determining the Size of the Scaling-Resistor Pack Installing the Scaling-Resistor Pack and W-Jumpers Determining and Setting the Synchro Turns Ratio

Stepper Interface Testing the Gyro Interface Gyro Cable

CHAPTER 5 - SPECIFICATIONS

Specification Overview Water Velocity Specifications Profile Parameters Bottom Track Specifications Echo Intensity Profile Transducer and Hardware Specifications Internal Sensors System Power Specifications Environmental Specifications Outline Installation Drawings

Ocean Surveyor/Observer Electronics Chassis - 96A-6000 Ocean Surveyor/Observer 38 kHz – 96A-6009 Ocean Surveyor/Observer 75 kHz - 96A-6007 Ocean Surveyor/Observer 75 kHz, Wide Flange - 96A-6011 Ocean Surveyor/Observer 150 kHz - 96A-6018 Ocean Surveyor/Observer 150 kHz, Flanged – 96A-6019

APPENDIX A - DRY CONNECTOR INSTALLATION

Dry Connector Installation Overview Installation Instructions Checking the Wiring

LIST OF FIGURES

Figure 1. I/O Cable Connector Configurations Figure 2. Typical Ocean Surveyor/Observer Interface Cable Layout (Overview) Figure 3. Typical Ocean Surveyor/Observer Interface Cable Layout (Detail View) Figure 4. OS2 versus an OS1 I/O Cable Wet-End Connector (Wire Side View) Figure 5. Check for O-Ring Installation on Cable and End-Cap Figure 6. Transducer Misalignment Reference Points Figure 7. Conceptual Drawing of an Acoustic Window with Mounting Ring Figure 8. Location of the Window Bolt Hole Circle Diameter Figure 9. Ideal Drain Hole Locations Figure 10. 38 kHz Insertion Loss (one-way) with a 19.1mm window at 0°C Figure 11. 38 kHz Insertion Loss (one-way) with a 38.1mm window at 0°C Figure 12. 75 kHz Insertion Loss (one-way) with a 9.5mm window at 0°C Figure 13. 75 kHz Insertion Loss (one-way) with a 9.5mm window at 0°C Figure 14. 75 kHz Insertion Loss (one-way) with a 19.1mm window at 0°C Figure 15. 75 kHz Insertion Loss (one-way) with a 19.1mm window at 0°C Figure 16. 150 kHz Insertion Loss (one-way) with a 9.5mm window at 0°C Figure 17. 150 kHz Insertion Loss (one-way) with a 9.5mm window at 0°C

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Figure 18. 150 kHz Insertion Loss (one-way) with a 19.1mm window at 0°C Figure 19. 150 kHz Insertion Loss (one-way) with a 19.1mm window at 0°C Figure 20. Inside Vessel Mounting - OS 38 kHz Transducer Figure 21. Underneath Vessel Mounting - OS 38 kHz Transducer Figure 22. Inside Vessel Mounting - OS 75 kHz Transducer Figure 23. Underneath Vessel Mounting - OS 75 kHz Transducer Figure 24. Inside Vessel Mounting - OS 150 kHz Flanged Transducer Figure 25. Underneath Vessel Mounting - OS 150 kHz Flanged Transducer Figure 26. Gyro Interface Board Figure 27. Cable, Gyro Synchro/Stepper to Electronic Chassis (J2) Figure 28. Pigtail Cable Construction Figure 29. I/O Cable Wiring (73A-6010)

LIST OF TABLES

Table 1: Trigger-In Input/Output Signals Table 2: Expected Loss for ADCPs with 30Degree Beam Angle Table 3: Expected Loss for ADCPs with 20Degree Beam Angle Table 4: Wavelength of sound in seawater (1500 m/s sound speed) Table 5: Gyro Interface Options by Model Table 6: Acceptable Gyro Interface Configurations Table 7: Standard Synchro Stator Voltages and Scaling Resistance Table 8: Natel Chip, Resistor Pack, and W-jumper Sockets Table 9: Gyro Interface Switch 1 Settings Table 10: Gyro Interface Switch 2 Settings Table 11: Stepper Voltage Range Table 12: Gyro Interface Troubleshooting Guide Table 13: Water Profiling – Long Range Mode Table 14: Water Profiling – High Precision Mode Table 15: Water Profile Maximum Ping Rate Table 16: Maximum Bottom Track Altitude Table 17: Outline Installation Drawings

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REVISION HISTORY

April 2014

• Updated specifications

December 2012

• Updated revision date to match operation manual

August 2012

• Updated styles and fonts.

• Added corrections from ICN102 (150 kHz Conceptual Well Design did not show the current flanged design of the transducer).

• Added corrections from ICN123 (updated the storage and operating temperature specifications).

• Added corrections from ICN138 (The 96A-6009 outline installation drawing did not specify the lifting bolt holes or the Beam 3 notch).

• Added corrections from ICN139 (updated the 96A-6018 and 96A-6019 outline installation draw-ings for the 150 kHz systems).

• Added correction to I/O cable diameter.

• Updated Dry Connector Installation.

EXCLUSIONS AND OMISSIONS

1: None

NOTES

Ocean Surveyor / Ocean Observer Installation Guide April 2014

Chapter 1

AT A GLANCE

In this chapter, you will learn:

• System overview

• Installation overview

• Alignment overview

April 2014 Ocean Surveyor / Ocean Observer Installation Guide

Introduction This book is a guide for installing a Teledyne RD Instruments (TRDI) Ocean Surveyor/Observer Acoustic Doppler Current Profiler (ADCP) aboard a vessel (ship) or platform. Use this book to plan your installa-tion layout. You also can use this book to see what requirements you must consider before purchasing an ADCP. We recommend you distribute this book to your organization’s decision-makers and installation engineers.

TRDI is not an expert in installing the ADCP aboard a ship. There are too many installation methods. We suggest you seek expert advice in this area because of its importance in ADCP performance. However, we can give you information about how others have installed their systems. In return, we do appreciate receiving information about your installation and the results.

How to Contact Teledyne RD Instruments If you have technical issues or questions involving a specific application or deployment with your instru-ment, contact our Field Service group:

Teledyne RD Instruments Teledyne RD Instruments Europe

14020 Stowe Drive Poway, California 92064

2A Les Nertieres 5 Avenue Hector Pintus 06610 La Gaude, France

Phone +1 (858) 842-2600 Phone +33(0) 492-110-930

FAX +1 (858) 842-2822 FAX +33(0) 492-110-931

Sales – rdisales@teledyne.com Sales – rdie@teledyne.com

Field Service – rdifs@teledyne.com Field Service – rdiefs@teledyne.com

Client Services Administration – rdicsadmin@teledyne.com Web: http://www.rdinstruments.com

24/7 Technical Support +1 (858) 842-2700 mailto:rdisales@teledyne.com mailto:rdie@teledyne.com mailto:rdifs@teledyne.com mailto:rdiefs@teledyne.com mailto:rdicsadmin@teledyne.com http://www.rdinstruments.com/

Ocean Surveyor/Observer Overview The standard Ocean Surveyor/Observer is an AC-powered, two-part unit. It consists of a bronze transduc-er assembly mounted in the ship’s hull and an electronics chassis you can place in the ship’s lab. Several options are available.

The basic system includes:

• Transducer assembly - Contains the transducer ceramics and electronics. Standard acoustic frequencies are 38, 75, and 150 kHz. See the outline drawings for dimensions and weights.

• Electronics chassis - Contains the processing electronics.

• Maintenance kit - Contains spare parts and basic tools needed for routine maintenance.

• Ocean Surveyor/Observer technical manual and user’s guide.

• Waterproof dummy plug.

• VmDas Software - Controls the ADCP and displays its data through a Windows compatible computer.

• Utilities software - Several programs to help you view data (WinADCP) and talk directly to the ADCP and other utility programs (RDI Tools).

Standard options include:

• Input/Output (I/O) cables and connectors (length determined by customer).

• Gyrocompass (gyro) interface - Connects the ship’s gyro to the electronics chassis.

Power Considerations The Ocean Surveyor/Observer uses 1600 watts of peak power. Teledyne RD Instruments recommends using a UPS system with a rated output power of at least 2400 watts.

All Ocean Surveyor/Observer ADCPs draw the same amount of peak current and inrush current (power up current draw). They will also draw the same average power assuming that they are setup the same.

There is no frequency dependence on the power requirement. All Ocean Surveyor/Observer ADCP fre-quencies (38, 75, and 150) use the same amount of peak power, 1600 Watts. The only difference is the duration that they draw the peak power.

Here are the power specifications for all Ocean Surveyor/Observer ADCPs:

Input Voltage: 90-250VAC

Frequency: 47-63Hz

Input Power (between transmit): 60W (typical)

Input Power (peak): < 1600W

Inrush Current @ 115/230VAC: 17/34 Amps rms

Ride through time: 20ms

Transient surge: EN/IEC 1000-4-2 Level 4

Common mode & normal mode: EN/IEC 1000-4-5 Level 3

To decide which UPS system to use you must be able to handle more power than the maximum (peak) power that will be needed to operate the Ocean Surveyor/Observer ADCP. This means you do not want to use a UPS system that only provides 1600W, it must provide more than this.

To determine the acceptable requirements for a UPS, you must determine the derating factor you will use.

The recommended derating factor is 50% and the minimum derating factor you would use is 75%. Using the recommended derating factor (50%) means that you need a UPS capable of supplying 3200 Watts. If you use the minimum derating factor then you would use a UPS capable of supplying 2133 Watts.

The UPS must be able to handle the inrush current as well. Inrush current is the current required to fully charge up the power supply when power is applied to the electronic chassis. This is particularly true for cases where the system is supplied with 230 VAC, as the inrush current is as high as 34 Amps rms. If the UPS limits the current, then the power on cycle will take longer. You do not want the UPS to shut down during the inrush current draw, as this may not allow the Ocean Surveyor/Observer ADCP electronics to start.

TRDI recommends a dedicated AC circuit protected by a 20 Amp (115 VAC) or 40 Amp (230 VAC) circuit breaker.

One UPS used by a customer provided 2400 Watts, which provides a derating factor of 67%. This is basi-cally half way between the minimum derating factor and the recommended derating factor. This UPS pro-vided adequate power for the OS38 and appeared to not be pushing the UPS beyond a reasonable safety point. Therefore, a UPS system providing 2400 Watts is Teledyne RD Instrument’s recommendation for all Ocean Surveyor/Observer and Ocean Observer ADCPs.

Computer Considerations We designed the Ocean Surveyor/Observer system to use a Windows® compatible computer. The com-puter controls the ADCP and displays its data, usually through our VmDas program.

It is highly recommended that you download and install all of the critical updates, recommended updates, and the service releases for the version of Windows® that you are using prior to installing any TRDI software.

VmDas requires:

• Windows XP® or Windows 7®

• Pentium III 600 MHz class PC (higher recommended)

• 1GB of RAM (2GB or more RAM recommended)

• 50 MB Free Disk Space plus space for data files (A large, fast hard disk is recommended)

• Minimum of one serial port; number of ports is dependent on the application. VmDas can use up to six serial ports in some configurations (High Speed Serial Ports recommended).

• Minimum display resolution of 1024 x 600, 768 color

• CD-ROM Drive

• Mouse or other pointing device

• An Ethernet card if network I/O is desired

The computer configuration varies depending of the number of communication ports and the external data refresh rate. Serial communications require a lot of processor resources, and the minimum require-ments can vary. A good quality video card is required to operate VmDas and WinADCP simultaneously.

We do not use graphic card 3D functions, however, video memory is needed to display all graphics.

However, with experience we can recommend that:

• If you are using more than two communication ports, you should not use a Celeron processor.

• Intel Pentium III processors work best to operate the ADCP and give access to display and keyboard without losing ensembles.

Electronics Chassis Considerations Place the electronics chassis (see Outline Installation Drawings) where there is access to the I/O cable, host computer, gyro interface cable, and navigation interface cable. You can place the rack-mountable chassis in a standard 19-inch cabinet. The chassis needs 90 to 260 VAC to operate (see Power Considerations). Al-low enough room around the chassis for access, ventilation, and isolation from electronic and magnetic interference.

Cabling Considerations Several cables connect to the Ocean Surveyor/Observer system (Figure 2 and Figure 3). Use care when routing these cables through bulkheads, deck plates, cable runs, and watertight spaces. Make allowances in cable length and engineering design plans for cable routing. When necessary, use strain reliefs on the cables.

The input/output (I/O) cable (Figure 1 and Figure 29) connecting the transducer assembly to the elec-tronics chassis has the following specifications.

• Minimum bend radius = 203 mm (8.0 in.)

• Typical cable OD = 19.507 mm (0.768 in.) minimum to 21.894 mm (0.862 in.) maximum

• Maximum pull load = 1132 N (250 lb.)

• Maximum length = 100 m (328 ft.)

• Available with either ends having straight or angled connectors or a combination thereof. The transducer-end connector is molded on, so you can use it below the waterline.

The I/O cable (wet end) uses a 2-022 O-ring. Always check that the I/O cable O-ring is in place when connecting the I/O cable to the transducer. The 2-022 O-ring has a tendency to fall out if the cable connector is dropped.

Do not place the electronic chassis within three feet of a computer monitor. Monitors are a major source of electronic interference.

Figure 1. I/O Cable Connector Configurations

Route this cable so:

• You can install it with the connectors attached.

• It does not have kinks or sharp bends.

• You can easily replace it if it fails.

You can order the cable with the chassis-end connector removed. This allows easier cable routing, but requires you to assemble the cable connections at your installation site (see Dry Connector Installation). This is a difficult task.

Other cables that may need routing to the chassis include the computer serial interface, gyro interface, and Trigger In/Out. Other cables that may need routing to the computer include the navigation interface and the remote display interface.

Figure 2. Typical Ocean Surveyor/Observer Interface Cable Layout (Overview)

19.507 min

21.894 max

19.507 min

21.894 max

COMPUTER

ENSEMBLE OUT

(OPTIONAL)

NAVIGATION DEVICE

(OPTIONAL)

G Y R O /R E P E AT E R A N D

IN T E R FA C E C A B LE

ELECTRONICS

CHASSIS

T R A N S D U C E R

A S S E M B LYS E R IA L C A B L E

I/O CABLE

Figure 3. Typical Ocean Surveyor/Observer Interface Cable Layout (Detail View)

I/O Cable Identification Both the OS1 and OS2 Ocean Surveyor/Observer I/O cables use the same raw cable (97A-6002-00). Addi-tionally, the dry end connectors are exactly the same on the OS1 and OS2 cables. The only external differ-ence is the wet end connectors. These are different on the OS1 and OS2 cables. Internally the cables are wired differently. If you are in doubt about what cable to use, use Figure 4 to identify the OS2 cable.

Figure 4. OS2 versus an OS1 I/O Cable Wet-End Connector (Wire Side View)

2 COM PORTS

- ADCP

- NAV (GPS)

OR

3 COM PORTS

- ADCP

- NAV (GPS)

- GYRO (NMEA)

GPS - $GGA

GPS - $VTG

HEADING - $HDT

HEADING - $HDG

PITCH/ROLL - $PRDID

$HDT or $HDG

OS2 Cable OS1 Cable

Navigation Interface Considerations VmDas can read in, decode, and record ensembles from an ADCP and NMEA data from some specific (i.e.

GPS and attitude sensors) external devices. VmDas stores this data in both raw data files (leaving all orig-inal data input in its original format) and in a combined, averaged data file. VmDas uses all of this data to create different displays for the user.

VmDas looks for, and utilizes the following strings if transmitted: standard GGA (position), HDG/HDT (Heading), VTG (speed and track) messages, and a proprietary PRDID (pitch and roll) message.

As well as being able to input NMEA strings to VmDas, it can produce NMEA output strings of speed log information. The speed log contains VDVBW (ground/water speed) and VDDBT (depth).

For more information about NMEA data, see the VmDas User’s Guide.

Using Trigger-In and Trigger-Out The Trigger Input allows the Ocean Surveyor/Observer to be synchronized by an external +5Vlogic level signal. The minimum duration for the Trigger Input is 1ms. The Input resistance is at least 2.7 kOhm. The Trigger Output is a +5V logic level signal as well. The nominal source resistance of the Trigger Output is 50 Ohms.

The Trigger Output and Input is controlled by the CX a,b command, where a controls the Trigger Input mode, and b the Trigger Output mode. For flexibility, several modes for the Trigger Input and Output op-eration have been implemented. See Table 1 for a description of the command.

Trigger-In is available only for systems using firmware version 23.xx or later and using the new electronics chassis back panel.

The Trigger In and Trigger Out B-N-C connectors use the center post as the signal input. The outside of the B-N-C connector is used for ground.

The ADCP performs a cycle of reading sensors (known as overhead), transmitting, blanking, processing, and sleep for each ping. When the CX command is enabled (by any setting of CX other than CX0,0), the ADCP will enter a transmit trigger wait state just before the transmitting portion of the cycle. It is during this wait state that the Trigger In input is read by the ADCP. This results in the following caution:

The ADCP does not store trigger in inputs. This means that the ADCP will only acknowledge pulses it sees during the transmit trigger wait state. For example, if three trigger in pulses were sent to the ADCP in quick succession only the pulse that occurred during the transmit trigger wait state would be used. The other pulses would be ignored and lost.

The setting of the CX command tells the ADCP what type of input signal (either pulse or a DC level) will be sent as the trigger. The following are the available inputs:

Table 1: Trigger-In Input/Output Signals Command Action: Description

CX 0,b Trigger Input off Normal operating mode.

CX 1,b Positive edge Trigger Input

Used if Ocean Surveyor/Observer is to be Triggered by other equipment. One ping is executed on every rising edge of the Trigger signal. Care has to be taken by the user not to exceed the maximum allowable transmit duty cycle of 15%.

CX 2,b Negative edge Trigger Input

Used if Ocean Surveyor/Observer to be Triggered by other equipment. One ping is executed on every falling edge of the Trigger signal. Care has to be taken by the user not to exceed the maximum allowable transmit duty cycle of 15%.

CX 3,b Any edge Trigger Input Used if Ocean Surveyor/Observer to be Triggered by other equipment. One ping is executed on every rising and falling edge of the Trigger signal. Care has to be taken by the user not to exceed the maximum allowable transmit duty cycle of 15%.

CX 4,b High level Trigger Input Used if Ocean Surveyor/Observer to be Triggered by other equipment. The OS transmits pings as long as the High level of the Trigger signal is present. In this way, a single ping or multiple pings can be transmitted depending on the duration of the High level. Care has to be taken by the user not to exceed the maximum allowable transmit duty cycle of 15%. A time between pings has to be set for cases where multiple pings should be transmitted.

CX 5,b Low level Trigger Input Same as CX 4,b except the Trigger is active at the low-level of the Trigger signal.

Care has to be taken by the user not to exceed the maximum allowable transmit duty cycle of 15%. A time between pings has to be set for cases where multiple pings should be transmitted.

CX a,0 Trigger Output off Normal operating mode.

CX a,1 Trigger Output – XMT The Trigger Output is at a high level during the time the Ocean Surveyor/Observer transmits.

CX a,2 Trigger Output – RCV The Trigger Output is at a high level during the time the Ocean Surveyor/Observer receives.

CX a,3 Trigger Output – X/R

The Trigger Output is at a high level during the time the Ocean Surveyor/Observer transmits and receives.

CX a,4 Trigger Output – in-verted X/R Trigger

Identical to CX a,3, except the signal is inverted. The Trigger Output is at a high level while the OS is not transmitting or receiving.

Installation Overview Read these steps before doing them. In general, follow them in the order listed. Some may differ for your installation, so modify them as necessary. Some can be done simultaneously (e.g., hardware installation and software loading). If you have problems or questions, call us.

1. On receipt of the system, read the Setup Card and check that you have all of the Ocean Survey-or/Observer equipment.

2. Before installing the system, test the transducer and electronics chassis right out of the shipping con-tainer. Do the following:

a. All power to the system DISCONNECTED.

b. Review Power Considerations.

c. Connect the I/O cable from the electronics chassis to the transducer.

d. Connect the serial I/O cable from the computer to the electronics chassis.

e. Connect the power cable to the electronics chassis and apply power to the system (see Figure 3).

f. Follow testing procedures in the Ocean Surveyor/Observer Technical Manual. Test the system. If errors occur, use the Troubleshooting section.

Do NOT ping the Ocean Surveyor/Observer with the transducer in air. The power assembly board will short, causing the electronics chassis to no longer communicate. The transducer is pinged by sending a CS or PT5 command or if VmDas is started for collecting data – either of these methods will cause damage if the transducer is in air.

3. Prepare the system for shipboard installation. Disconnect all power to the system. Disconnect all in-terface cables.

4. Review Transducer Mounting Considerations. Install the transducer head.

Take steps to prevent leaks through the hull and gate valves.

5. Mechanically align the system (see Alignment Overview).

6. Review Electronics Chassis Considerations. As necessary, do the following.

a. Check all switch settings on the gyro board (shown in Determining and Setting the Synchro Turns Ra-tio).

b. Install the electronics chassis.

7. Review Computer Considerations. Install the computer.

8. Review Cabling Considerations. As necessary, route and connect the following cables:

• Transducer to chassis (J1) interface cable.

The I/O connector on the transducer uses a 2-020 O-ring.

The I/O cable (wet end) uses a 2-022 O-ring. The 2-022 O-ring has a tendency to fall out if the cable connector is dropped.

Always check that both O-rings are in place when connecting the I/O cable to the transducer. If either O-ring is missing, the ADCP will flood.

Figure 5. Check for O-Ring Installation on Cable and End-Cap

• Gyro to chassis (J2) cable.

Signals may be present from the gyro.

• Navigation to computer cable.

Signals may be present from the navigation device.

9. As necessary, load the software on the computer’s hard drive. See the software User's Guides and the

Readme.txt files for each program.

10. Configure VmDas. See the VmDas User’s Guide for help on configuring VmDas.

11. Do the Dock Side Tests (see the Ocean Surveyor/Observer Technical Manual, Test section). If errors occur, use the Troubleshooting section.

12. Do the Sea Acceptance testing (see the Ocean Surveyor/Observer Technical Manual, Test section).

The Sea Acceptance tests include:

• Interference

• Water Profile Range

• Ringing (cross-coupling, other pingers, noise)

• Water Profile Reasonableness (transducer alignment)

• Bottom-track (range, accuracy)

Detailed View

2-022 O-Ring

2-020 O-Ring

2-257 Bore O-Ring 2-259 Face O-Ring

I/O Cable

End-Cap

Alignment Overview

This section does not apply to stationary systems (such as Oil Rig platforms). These systems use an internal compass by default.

The mechanical alignment of the transducer head is important to ADCP data accuracy. Mechanically mount the head as close as possible to your reference point. This is usually with the Beam 3 mark at 0° or 45° relative to the ship’s fore-to-aft centerline. You also must mount the transducer head as level as possi-ble using the ship’s roll and pitch references. Review the Transducer Mounting Considerations for alignment considerations.

VmDas uses the Heading Correction Parameters on the Transforms tab to align the ADCP’s north reference (Beam 3 mark) to the north reference of an external gyro/compass. Ships use the bow as the north reference.

When the Ocean Surveyor/Observer is aboard a vessel, the mechanical alignment of the transducer head (Beam 3 mark) is usually aligned with the ship’s fore-to-aft centerline (0°) or rotated 45° clockwise. To conceptually determine the misalignment angle, visually hold the ADCP still and turn the ship gyro’s north reference to match the ADCP’s north reference. For example, if the Beam 3 mark is pointing at the bow (Figure 6), the misalignment angle is zero. If the Beam 3 mark is pointing 45° to starboard (Figure 6), you must turn the ship gyro’s north reference a +45° to align the two north reference points. Conversely, if the Beam 3 mark is pointing 45° to port, you must turn the ship gyro’s north reference a -45° to align the two reference points.

Figure 6. Transducer Misalignment Reference Points

BEAM 3 MARK AT 0 DEGREES

TO SHIP CENTERLINE

BEAM 3 MARK ROTATED 45 DEGREES

FROM SHIP CENTERLINE

FORWARD FORWARD

Chapter 2

TRANSDUCER INSTALLATION

• Transducer mounting considerations

• Location

• Orientation

• Other considerations

Transducer Mounting Considerations You must consider several potential problems before installing the transducer assembly. Read this section before deciding where to install the transducer assembly. See the outline installation drawings (see Outline Installation Drawings) for specifications on our standard Ocean Surveyor/Observer transducer.

Location Ideally, you want to install the transducer assembly:

• Where it is accessible both internally (for access to transducer electronics) and externally (to remove biofouling).

• Where the I/O cable length is 100 m (328 feet) or less.

• Away from shipboard protrusions that reflect ADCP energy. Allow for a reflection-free clear-ance of 15° around each beam (see the outline installation drawings).

• Away from other acoustic/sonar devices, especially those operating at the same frequency (or harmonic) of the ADCP.

• Close to the ship’s fore-to-aft centerline. As distance from the centerline increases, vertical ac-celerations caused by the roll of the ship also increase. These accelerations can cause addi-tional uncertainties in ADCP velocity measurements.

Orientation The 38 kHz oval transducer should always be mounted with the transducer’s beam 3 mark on axis (for-ward). If you have a round Ocean Surveyor/Observer transducer, then we recommend you mount the transducer head with the Beam 3 mark rotated to a ship-relative angle of 45°. Figure 6 shows the beam orientation. This causes the magnitude of the signal in each beam to be about the same. This improves error rejection, reduces the effect of ringing (see Acoustic Isolation), and increases the ADCP’s effective ve-locity range by a factor of 1.4. If you align Beam 3 at an angle other than zero, you must nullify this offset (see Alignment Overview). You can do this through our VmDas program or using a direct command.

Use the ship’s roll and pitch reference to mount the transducer head as level as possible. If the head is not level, depth cell (bin) mapping will be incorrect. Large misalignments can cause large velocity measure-ment errors. If you cannot mechanically make the transducer head level, you can use VmDas to enter off-set values for roll and pitch, or use direct commands for roll/pitch offsets (see Alignment Overview).

Other Considerations Once you have chosen a mounting location and orientation, take into consideration the following sections.

Floating Objects Our transducer assembly is sturdy, but we did not design it to withstand collisions with all floating ob-jects. We strongly suggest you use one of the following.

Acoustic Window While we do not fully understand windows, we do believe that windows can be used to produce overall performance improvements in vessel-mounted ADCPs. Additionally, if the ship operates where there is danger of barnacle damage or a high density of ice or other floating objects, then the use of an acoustic window is the only option. For more information, see Using Acoustic Windows.

Sea Chest A sea chest is a fixture that surrounds and holds the transducer head, protecting it from debris in the wa-ter. The bottom of the sea chest must be open to seawater to allow the acoustic beams to pass through freely. For more information, see Conceptual Transducer Well Design.

Fairing A fairing is a structure that produces a smooth outline and reduces drag or water resistance. The fairing also diverts floating objects away from the transducers. A fairing shaped like a teardrop, slopped such that the leading edge (closer to the bow) is higher than the back edge, and extends below the hull (typically 12 inches) will divert the air bubbles away from the transducer faces.

Air Bubbles Design your installation to minimize the volume of air bubbles in the path of the acoustic beams. Air bub-bles attenuate (weaken) the signal strength and reduce the ADCP profiling range. Ships with a deep draft or a non-flat bottom have fewer problems with bubbles. Ways to reduce bubble flow vary with ship char-acteristics, but two options are available. Mount the transducers below or away from the bubble layer.

• The flow layer is usually within the first two feet below the hull. Bubbles can be trapped in this layer. Mounting the transducer head amidship on the fore-to-aft centerline may help. For ships with propulsion systems that make large amounts of bubbles, use a mounting technique that lets you lower the transducer head below the hull while underway.

If you use locally made or existing extension hardware instead of the hardware available from TRDI, you may need to make an adapter plate to connect your hardware to our transducer head. See Outline Installation Drawings for the bolt hole locations.

• Divert the bubble layer so it flows around the transducers - You can use fairings to alter the bubble flow (see Fairing). An acoustic window (see Acoustic Window) may help reduce the bub-ble problem, but can cause ringing (see Acoustic Isolation) and attenuation problems.

Flow Noise Water flowing over the transducer faces increases the acoustic noise level, which decreases the profiling range of the ADCP. You can reduce the flow across the transducer faces with a sea chest, fairing, or acous-tic window.

Corrosion and Cathodic Disbondment Never attach anodes directly to the transducer head. Additional anodes or impressed voltage systems can cause the urethane to separate from the transducer (cathodic disbondment) or cause the material of the transducer to break down. Standard anode protection used for the ship should be installed outside of the well of the transducer head. Mounting of ship’s standard anode protection outside of the transducer well will typically not cause any problems. Our transducers are made of a material that has shown to corrode very little over time when the above precautions are met. The corrosion can be further reduced if the well is covered with a window and then filled with fresh water.

Ringing The ADCP transmits an acoustic pulse into the water. The main lobe of this pulse bounces off particles in the water and the signals returned from these particles are used to calculate the velocity of the water.

As stated, the main lobe of the transmitted pulse is what we are using to process and calculate a velocity.

The transmitted pulse, however, is made up of many side lobes off the main lobe. These side lobes will come in contact with metal of the transducer beam itself and other items in either the water or the well.

The energy from the side lobes will excite the metal of the transducer and anything bolted to the transduc-

er. This causes the transducer and anything attached to it to resonate at the system’s transmit frequency.

We refer to this as ringing.

If the ADCP is in its receive mode while the transducer is ringing then it will receive both the return sig-nals from the water and the ringing. Both of these signals are then processed by the ADCP. The ringing causes bias to the velocity data.

All ADCPs ring for some amount of time. Therefore, each ADCP requires a blanking period (time of no data processing) to keep from processing the ringing energy. Each ADCP frequency has a different typical ringing duration. The typical ringing period for each ADCP frequency is as follows; 38 kHz is 16 meters, 75 kHz is 8 meters, and 150 kHz ADCPs is 4 meters. These typical ringing values are recommended as the minimum setting for all ADCPs using default setups.

It should be noted, on some installations the effects of ringing will last longer than the recommended set-tings above. For example, the effects of ringing will last longer if the transmit signal becomes trapped in-side the transducer well. This can occur because the well itself is ringing with the transducer or when win-dows covering the opening of the well reflect the signal back inside the well.

The window causes the transmit signal to reflect back into the well due to the difference in impedance be-tween the window and the water. When the transmit signal is reflected in the well it becomes trapped and this results in longer ringing periods. To keep from processing this signal, the blanking period must be increased. Lining the inside walls of the well with a sound absorbing material aid in dampening the ring-ing effect.

Acoustic Isolation Try to minimize the acoustic coupling between the transducer head and the ship. Without adequate acoustic isolation, the transducer output will ring throughout the ship and feeds back into the ADCP re-ceive circuits. Ringing causes bias errors in water-track velocities and results in the loss of data in the closest depth cells (bins). Reflections inside a sea chest with an acoustic window also can cause ringing.

You can attain acoustic isolation several ways. At a minimum, use gaskets to isolate all contact points be-tween the ship and the transducer head. Design your installation for:

• A minimum number of contact points between the transducer head and the ship.

• Minimal contact area.

• Single points of contact for positioning and support (when possible).

You also should try to separate the transducer head from the ship using intermediate connections. This is because direct connections transfer the most acoustic energy. Texas A & M used the following installation technique and had minimal ringing problems.

• Transducer head mounted to a thin steel plate

• Steel plate positioned with three pins set into mounting holes on the hull; pins isolated with gas-kets

• Steel plate held in place with four I-beams welded to a frame

• Frame bolted to another frame and separated by gaskets

• Second frame bolted to the ship and separated by gaskets

Acoustic isolation from other acoustic devices on the ship is also necessary. You can do this using the fol-lowing techniques.

• Mount the other acoustic devices as far apart as possible.

• Make sure neither the main lobes nor the side lobes of the acoustic devices point at the transduc-ers, including acoustic reflections.

• Do not to operate devices that use the same frequency or a harmonic of the ADCP’s frequency.

Maintenance The Ocean Surveyor / Ocean Observer Technical Manual, Maintenance section explains routine mainte-nance procedures. You rarely need access to the electronics inside the transducer head. However, one ex-ternal maintenance item is important enough to mention here as it may affect how you install the trans-ducer head.

Objects deployed within about 100 meters (328 feet) of the surface are subject to the buildup of organic sea life (biofouling). This means Ocean Surveyor/Observers are subject to biofouling. Soft-bodied organ-isms usually cause no problems, but hard barnacle shells can cut through the urethane transducer face causing transducer failure and leakage into the ADCP.

The best-known way to control biofouling is cleaning the ADCP transducer faces often. However, in many cases this is not possible. The other alternatives include the use of a window or some sort of anti-foulant protection.

Some of our users have had success applying a thin coat (≈4 mm; ≈0.16 in.) of either a 50:50 mix of chili powder and Vaseline or chili powder and silicone grease to the transducer faces. The chili powder should be the hottest that can be found. Water flowing across the transducers will wash this mix away over time.

The silicone mixture tends to last longer.

Some organizations may decide to use antifouling grease. However, most antifouling greases are toxic and may cause problems. Recent tests suggest antifouling grease may cause the urethane on the transducer faces to develop cracks. Warmer temperatures accelerate this effect.

The other method is to use antifoulant paint. You can use almost any EPA approved anti-fouling paint on the housing or the urethane transducer face. Contact the antifouling paint manufacturer for preparation and application procedures.

Chapter 3

USING ACOUSTIC WINDOWS

• What is an acoustic window

• Material type and thickness of the window

• Insertion loss

• Conceptual transducer well design

Acoustic Window Overview Installation of an ADCP in a vessel is done in many ways, but typically the ADCP transducer is mounted inside of a sea chest or well. The opening of the sea chest or well can be open to the ocean or it can be cov-ered by an acoustic window.

An acoustic window is a covering that can seal the opening of the sea chest but still allow the acoustic sig-nal (both transmit and received signals) to be transferred through the window. The type, thickness, orien-tation, and other installation issues of the acoustic window are important to understand. If the wrong ma-terial is used or the wrong installation used then the performance obtained by the ADCP will be severely limited.

Background - Should I use an Acoustic Window?

Like any vessel-mount, acoustic system, the performance of the ADCP is sensitive to acoustic noise. For best performance, the transducer is mounted in its own well, recessed in the vessel hull, with an opening slightly larger than the transducer. An Acoustic Window, mounted across the well opening, is required to isolate the transducer face from flow noise, as the vessel moves through the water. Acoustic windows (or simply windows) can produce overall performance improvements in vessel-mounted ADCPs through the following advantages.

Advantages

• Well will not fill with air bubbles caused by the ship moving through the surface water.

• Flow noise is reduced.

• The well can be filled with fresh water to limit corrosion.

• Barnacles cannot grow on the transducer faces. Barnacle growth is the number one cause of failure of the transducer beams.

• The transducer is protected from debris floating in the water.

Although these advantages are important, it should be known that if the wrong window is used or if the window is not installed properly then the following disadvantages are possible.

Disadvantages

• The range of the ADCP can be reduced because the window will absorb some of the transmit and receive energy.

• The transmit signal could be reflected into the well, causing the well to ring like a bell. This will cause the data being collected during the ringing to be biased. Some ships have reported a loss in range as great as 50 meters. Applying sound absorbing material on the well walls may dampen the ringing.

• The transmit signal could be reflected off of the window and back into the other beams.

However, even though there are disadvantages possible our experience has shown that when the correct window is used and it is properly installed that the window advantages are far more important. The re-mainder of this Application Note will focus on how to choose the window for your vessel, how to mount the window, how to maintain the window, and any other associated concerns when using a window.

What Window should I use?

While we cannot claim to understand every window, we do believe that we can recommend a material that will work. We have developed a simple model for an acoustic window made from polycarbonate material.

Over the past 2 decades we have obtained feedback from customers that have allowed us to prove the model is a fair estimation of what to expect for performance. Polycarbonate was chosen because it can provide enough strength for most installations, is readily available in most countries, it has been shown to last a long time (over 7 years in some installations), and it can be used on all ADCP models (NarrowBand (NB), BroadBand (BB), WorkHorse (WH), and Ocean Surveyor (OS)).

The type of ADCP model is very important when choosing a window. The bandwidth of the acoustic signal from the ADCP must be maintained. Different window materials have different losses over a band of fre-quencies. As an example, the Ocean Surveyor/Observer ADCP uses a bandwidth of 6% or 1% about the system’s center frequency. A BroadBand or WorkHorse ADCP uses a bandwidth of 25% or 6% about the system’s center frequency. The material polycarbonate has a fairly uniform loss about these frequency bandwidths.

It should be noted that we have no knowledge about the variability of polycarbonates. And so, the acoustic model that we run is for a particular polycarbonate manufactured by Zelux. This is a window-grade, poly-carbonate and has a high tensile strength (~9000psi) to resist cracking.

Even when choosing this particular window it is important to choose the proper thickness of window ma-terial. A window will absorb sound and reduce the range of the ADCP. Therefore, we always recommend using the thinnest window possible. However, depending on your application a thicker material may be necessary. The following table indicates the expected loss (two-way) of polycarbonate at different frequen-cies and thickness.

Table 2: Expected Loss for ADCPs with 30Degree Beam Angle Frequency

(kHz) Thickness mm (in.) One-way loss @ 0°,20°,40°C (dB) Two-way loss @ 0°,20°,40°C (dB)

Expected Loss in Range (meters)

38 76.2 (~3.0) 2.7 2.6 2.3 5.4 5.2 4.6 173

38 63.5 (~2.5) 3.0 2.9 2.5 6.0 5.8 5.0 192

38 50.8 (~2.0) 2.9 3.2 2.9 5.8 6.4 5.8 205

38 38.1 (~1.5) 1.4 1.2 1.0 2.8 2.4 2.0 90

38 25.4 (~1.0) 2.9 3.3 3.3 5.8 6.6 6.6 211

38 19.1 (~0.75) 1.0 0.9 0.8 2.0 1.8 1.6 64

38 12.7 (~0.5) 5.3 5.8 5.6 10.6 11.6 10.2 371

38 9.5 (~0.375) 1.8 1.8 1.8 3.6 3.6 3.6 115

38 6.4 (~0.25) 0.7 0.7 0.6 1.4 1.4 1.2 45

75 76.2 (~3.0) 4.2 4.3 3.8 8.4 8.6 7.6 138

75 63.5 (~2.5) 3.9 4.0 3.5 7.8 8.0 7.0 128

75 50.8 (~2.0) 3.6 3.6 3.0 7.2 7.2 6.0 115

75 38.1 (~1.5) 2.7 2.6 2.3 5.4 5.2 4.6 83

75 25.4 (~1.0) 3.1 3.3 2.9 6.2 6.6 5.8 106

75 19.1 (~0.75) 1.4 1.2 1.0 2.8 2.4 2.0 45

75 12.7 (~0.5) 3.1 3.5 3.3 6.2 7.0 6.6 112

75 9.5 (~0.375) 1.0 0.8 0.7 2.0 1.6 1.4 32

75 6.4 (~0.25) 5.9 6.3 5.5 11.8 12.6 11.0 202

150 50.8 (~2.0) 5.0 5.2 4.6 10.0 10.4 9.2 83

150 38.1 (~1.5) 4.2 4.4 3.8 8.4 8.8 7.6 70

150 25.4 (~1.0) 3.6 3.6 3.0 7.2 7.2 6.0 58

Frequency (kHz) Thickness mm (in.) One-way loss @ 0°,20°,40°C (dB) Two-way loss @ 0°,20°,40°C

(dB) Expected Loss in Range

(meters)

150 19.1 (~0.75) 2.7 2.6 2.3 5.4 5.2 4.6 43

150 12.7 (~0.5) 3.1 3.3 2.9 6.2 6.6 5.8 53

150 9.5 (~0.375) 1.4 1.2 1.0 2.8 2.4 2.0 22

150 6.4 (~0.25) 3.2 3.6 3.3 6.4 7.2 6.6 58

300 25.4 (~1.0) 5.0 5.2 4.5 10.0 10.4 9.0 42

300 19.1 (~0.75) 4.2 4.3 3.8 8.4 8.6 7.6 34

300 12.7 (~0.5) 3.6 3.6 3.0 7.2 7.2 6.0 29

300 9.5 (~0.375) 2.7 2.6 2.3 5.4 5.2 4.6 22

300 6.4 (~0.25) 2.9 3.4 3.2 5.8 6.8 6.4 27

TRDI’s recommended thickness is in blue bold. TRDI’s recommended maximum thickness is in red italic and bold in the above table. All other items will result in poor overall performance or a loss in range that most customers find unreasonable.

One-way insertion loss curves for all items above in bold (TRDI’s recommended thickness) are found in Appendix A of this application note. All other plots are available from TRDI upon request.

Note all of the losses and expected ranges are estimated and some of the assumptions we make may not be true in your installation. However, based on several actual installations the values shown have proven to be good estimations. Your actual loss may be higher or lower than what is shown.

Table 3: Expected Loss for ADCPs with 20Degree Beam Angle

Frequency (kHz) Thickness mm (in.) One-way loss @ 0°,20°,40°C (dB) Two-way loss @ 0°,20°,40°C (dB) Expected Loss in Range (meters)

38 76.2 (~3.0) N/A N/A N/A N/A N/A N/A N/A

38 63.5 (~2.5) N/A N/A N/A N/A N/A N/A N/A

38 50.8 (~2.0) N/A N/A N/A N/A N/A N/A N/A

38 38.1 (~1.5) N/A N/A N/A N/A N/A N/A N/A

38 25.4 (~1.0) N/A N/A N/A N/A N/A N/A N/A

38 19.1 (~0.75) N/A N/A N/A N/A N/A N/A N/A

38 12.7 (~0.5) N/A N/A N/A N/A N/A N/A N/A

38 9.5 (~0.375) N/A N/A N/A N/A N/A N/A N/A

38 6.4 (~0.25) N/A N/A N/A N/A N/A N/A N/A

75 76.2 (~3.0) 3.1 3.2 2.8 6.2 6.4 5.6 102

75 63.5 (~2.5) 2.7 2.8 2.6 5.4 5.6 5.2 90

75 50.8 (~2.0) 2.6 2.6 2.3 5.2 5.2 5.6 90

75 38.1 (~1.5) 2.0 2.0 1.8 4.0 4.0 3.6 64

75 25.4 (~1.0) 2.2 2.1 1.8 4.4 4.2 3.6 70

75 19.1 (~0.75) 0.9 0.9 1.0 1.8 1.8 2.0 32

75 12.7 (~0.5) 2.8 2.9 2.4 5.6 5.8 5.4 93

75 9.5 (~0.375) 1.0 0.9 0.8 2.0 1.8 1.6 32

75 6.4 (~0.25) 4.2 3.7 2.7 8.4 7.4 5.4 134

150 50.8 (~2.0) 3.6 3.8 3.4 7.2 7.6 6.8 61

150 38.1 (~1.5) 3.1 3.2 2.8 6.2 6.4 5.6 51

150 25.4 (~1.0) 2.6 2.6 2.3 5.2 5.2 4.6 42

150 19.1 (~0.75) 2.0 2.0 1.8 4.0 4.0 3.6 32

150 12.7 (~0.5) 2.2 2.1 1.8 4.4 4.2 3.6 35

Frequency (kHz) Thickness mm (in.) One-way loss @ 0°,20°,40°C (dB) Two-way loss @ 0°,20°,40°C (dB) Expected Loss in Range (meters)

150 9.5 (~0.375) 0.9 0.9 0.9 1.8 1.8 1.8 14

150 6.4 (~0.25) 2.9 2.9 2.3 5.8 5.8 5.6 46

300 25.4 (~1.0) 3.6 3.8 3.4 7.2 7.6 6.8 30

300 19.1 (~0.75) 3.1 3.2 2.8 6.2 6.4 5.6 26

300 12.7 (~0.5) 2.6 2.6 2.3 5.2 5.2 4.6 21

300 9.5 (~0.375) 2.0 2.0 1.8 4.0 4.0 3.6 16

300 6.4 (~0.25) 2.2 2.1 1.8 4.4 4.2 3.6 18

TRDI’s recommended thickness is in blue bold. TRDI’s recommended maximum thickness is in red italic and bold in the above table. All other items will result in poor overall performance or a loss in range that most customers find unreasonable.

One-way insertion loss curves for all items above in bold (TRDI’s recommended thickness) are found in Insertion Loss. All other plots are available from TRDI upon request.

Note all of the losses and expected ranges are estimated and some of the assumptions we make may not be true in your installation. However, based on several actual installations the values shown have proven to be good estimations. Your actual loss may be higher or lower than what is shown.

Are there any Other Windows that I can consider?

TRDI has only limited experience with other materials. As a result there is not much information we can provide about other materials. However, we can state that different materials will behave differently, de-pending on both the frequency and bandwidth of the acoustic ADCP signal. The absorption curves of vari-ous materials have significant amplitude fluctuations with frequency, which can change in both frequency and amplitude with changes in temperature.

Important acoustic properties of the window include acoustic refractive index (which should be as close as possible to that of water), insertion loss (which should be as small as possible) and speed of sound. There are two acoustic refractive indices: one for shear waves and one for plane waves. The acoustic refractive indices are simply the ratios of speed of sound in water to speed of sounds in the material. Insertion loss combines absorption and reflection of sound, and it depends on both the thickness and the material prop-erties of the window. In particular, you should avoid using window thickness equal to odd multiples of shear mode quarter-waves (Dubbelday and Rittenmeyer, 1987; Dubbleday, 1986). Refer to Selfridge (1985) and Thompson (1990) for more information. Note that the speeds of sound in plastics decrease with increasing temperature and that causes the resonant frequencies to shift. This can be a large effect.

Neither Selfridge nor Thompson has much information on the temperature…