[doi 10.1109%2foceans.1993.326194] forst, v.j.; pellen, a.t. -- [ieee oceans '93 - victoria,...

7/17/2019 [Doi 10.1109%2Foceans.1993.326194] Forst, V.J.; Pellen, A.T. -- [IEEE OCEANS '93 - Victoria, BC, Canada (18-21 O…

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TNE W I ' E G R A T I O N OF

A

HIGH

PERFORMANCE

FIBER

OPTIC TELEMETRY

SYSTEM

IN N ROV

Vincent

J.

Forst, Main

T.

Pellen

Perry

Technologies

Martin Marietta A ero and Naval Systems

100E. 17th St., Riviera Beach, Fl. 33404

Abstract

-

This

paper d escribes the integration of a

single fiber, full duplex, 5OOMbitls telemetry system

in an existing ROV, to up grade the existing hardwire

telemetry system . Benefits to

ROV

performance

include: additional video cha nnels, additional sensor

suites, electromagnetic interference (EMI)

free

signal

transmission, and improved ROV dynamic

performance. The paper analyzes the requirements of

the system and then provides a description of the

architecture that best satisfies those requirements.

Multiplexer and tether design issues are also

addressed.

1 O INTRODUCTION:

The fiber optic technology has enhanced the

ROV

industry in many ways because of its wide

bandwidth signal transmission. Along with the fiber

optic technology, high performance digital Time

Division Multiplexers (TDM) have increased the

capabilities

of

ROVs.

Laser sources and sensitive

wide bandwidth receivers allow loss budgets

exceeding 25 dB which provide great flexibility in the

interconnect cabling;

this

allows the use of multiple

rotary joints, connectors, and splices in the system.

Minimizing the umbilical and the tether cable

diameter so they can be spooled on the smalle st

winch

drum as

feasible was the goal of

this

design

effort. The power wire sizing optimization process

was

described in a previous paper by Mr. Pellen

see

reference [4]). In this paper, emphasis will be on the

optimization of c able diam eter through the integration

of a full duplex, SOOMbitls, digital TDM telemetry

system.

2.0 PERFORMANCEREQUIREMENTS:

The fiber optic system described here is to be

retrofitted on an existing ROV o reduce the tether

diameter from 6 cm to 4.5 cm. All existing functions

of the ROV must be preserved and be transp arent to

the operator

to

reduce retraining time and simplifi

the retrofit process.

As

a

minimum, the fiber optic

system must be able to transmit four simultaneous

video signals and four duplex

data

channels at 19.2

Kilo

baud on one single fiber. The system must be

compatible with the existing umbilical comprising

50/125 micron fibers and must have enough optical

power to transmit through 1.52km

of

fiber,

6

connectors, 11 splices, and

two

fiber optic rotary

joints

(FORJ).

3.0

DESIGN

APPROACH:

The system is being developed in four phases: the

preliminary design, the prototype development, the

detail design, and the retrofit phases. The first phase

consisted of preliminary design; architecture

of

the

system and hardware performance requirements were

defined; power budget, bandwidth calculation and

interconnect scheme evaluations were performed,

components such as multiplexers, slip ring

assemblies, and tether cab les were also specified; the

major components of the system including electronic

multiplexers, wave division multiplexers WDMs),

cable, and connectors were selected using a trade-off

analysis approach. The second phase consisted

of

building a prototype in the laboratory environment.

The purpose of prototyping was to mitigate the risk

of a new design and reduce the integration time

of

the

retrofit. All components of the system including

cables,

connectors,

splices, and fiber optic rotary

joints were breadboarded in the laboratory to

111-242 0-7803-1385-2193t 3 .~

1993 IEEE



simulate as close

as

possible the target

ROV

fiber

system. Power losses were measured

for

each

of

the

elements of the system using a light source and a

power meter as well as an optical time domain

reflectometer. The third phase, currently in progress,

consists

of

the detail design of the electronics

including electronic packaging and installation of

pressure vessels on the

ROV.

The fourth phase will

consist of retrofitting the fiber optics telemetry

system

to

the

ROV.

The integration will include

electronics pressure vessel installation, cabling

modification,

tether

refitting, and tether management

system modifications

to

accommodate the new fiber

optic tether.

ITEM

x

1

2

3

4

5

6

4.0

TELEMETRY SUBSYSTEM DESIGN

SYSTEM REQUIREMENTS:

The optical link components

shown in

Fig. 1 are

configured

as

a single fiber link. Wet connectors

provide quick disconnect of tether management

system, tether c able, and

ROV.

The

two

dual pass

fiber optic

r o w

oints FORJs) are located in an

umbilical winch slip ring and tether management

system slip ring.

COMPONENT

MIN MAX

COMPONENT

Loss

(de)

WDM 1 2

FORJ 2

4.5

SPLICE 0.1 0.5

STCO 0.5

1

W E T C O 0.5 1

50/125 FIBER 2.4 Km

3/Km

is desirable from an operations standpoint to provide

a spare

link,

therefore, a single fiber a rchitecture was

selected. After investigating the trade-offs between

the two approaches of a single fiber system, it was

decided to specifL

a

WD M. WDM insertion losses

are as low as

I ,

with good directivity and

isolation

-8OdB

directivity, -45dB isolation). The

power into a splitter is divided between the output

ports, according to the splitting ratio. If the ratio

is

50/50, the insertion

loss

is not less than

3dB.

The

decision was

made based on the lowest

loss

solution.

The use of WDMs in the system requires a dual

wavelength transm itterhece iver set a t both ends

of

the link. The minimum and maximum insertion

losses obtained from engineering

data

sheets of

specified optical components provided the basis for

estimating the

total

optical link loss. This data,

compiled

in

Table

1 ,

was used to establish the

minimum optical power budget required, by including

a safety margin, for the transmitterhceive r set.

111-243

Fig. 1

ROV

System Bi-Directional Optical Link

The existing ROV system cable configuration

provides spare fibers. With the dual pass FORTS, a

dual fiber

link

from top to bottom is possible. The

system architecture could be either dual fiber

or

single fiber depending on the approach selected.

A

single fiber system is possible by the use of wave

d iv ision m ul tip lexers O M S ) r optical couplers. It

2

2

11

3

3

1.5

2 4

4 9

1.1 5.5

1.5 3

1.5 3

1.5 1.8

TOTAL LINK LOSS (dB1 13 .7 29

Table 1

Optical Loss Budget

This Loss

Budget requires the use

of

a laser diode

sourcematched with a receiver that provides

a

power

budget of 26dB See power budget equ ation below).

= COMPONENT LOSSES SAFETY MAROtN [2]

'Tx-

'Ra

Actual link loss of the bread boarded system was

18dB

measured with a

1300nm

source. The measured

loss was less th n the computed average of estimated

link loss {minimum total link loss (dB) maximum

total link loss dB))/2 from Table 1 .

The

1.52km

link length was not bandwidth

limited per the bandwidth-length data provided by the

fiber manufacturer. The average

fiber

bandwidth

for

the 1.52km link is 625Mhz at 1300nm.



4.1 SUBSYSTEM ARCHITECTURE:

The fiber optic telemetry subsystem engineering

task was primarily focused on

specifying

a

video/duplex data multiplexer. As a minimum, the

multiplexer must provide

data

and video throughput

rates high enough

to

meet the current ROV

operational requirements, be integrated into a system

wt slip rings and electro-optical umbilical in place,

and provide expansion for future applications. The

multiplexer/demultiplexer interface architecture

is

shown in Figure 2.

DUPLEX DATA

VIDEO Rx

DUPLEX DATA

NTERFACE

MOWLE

COMPUTER

k SENSOR

CAMERAS

SUBSEA SENSORS CONTROL

I Ih

SURFACE

CONTROL

Fig. 2

ROV Telemetry System

4.2 MULTIPLEXER SELECTION:

A trade study was conducted to specify a

commercial

off

the shelf system that meets the

functional requirements, the derived optical power

budget and bandwidth restrictions addressed in

Section

4.0,

and the size restrictions imposed by an

already tightly packaged ROV. Eight fiber optic

video multiplexer systems were compared for

multiple video and full duplex data capability. From

these, the field

was

narrowed to

two

for packaging

reasons. The goal was to package the subsea

multiplexing equipment into a 20 cm. internal

diameter (I.D.) canister which will replace the

existing video canister and absorb video switching

and camera control functions. The remaining two

candidates were compared for size, optical power

budget, bandwidth, system growth capability, cost,

etc.

The

final

selection was based on optical power

budget performance and system growth capability.

The IpitekB IMTRAMm

CQ-4

DIGITAL VIDEO

OPTICAL TRANSMISSION SYSTEM

was

selected.

This was

the only system we found

that

offered a 25dB minimum power budget

in

transmit

and receive directions with a standa rd OdBm Fabry-

Perot laser source.

An

optional +3dBm distributed

feedback (DFB) laser source is available if required.

During prototyping, the pow er budget from

the CQ-4

system was measured at 27dB. The system also

provided superior duplex data capability which is

discussed

in

Paragraph

4.3.

he CQ-4 system is

made up of 3U high modules that plug into a 19-inch

wide Euro Chassis. For t h i s application, fou r video

A D modules and one digital time division

multiplexer/demultiplexermodule (M ux E ngine) will

be pack aged in a custom cha ssis which will fit in the

20cm. I.D.

canister

The exceptionaltechnical

staff

at IpitekB was kind enough to

work

with us in

designing and building

a

custom backplane and

chassis

to

our specification.

4.3

MULTIPLEXER INTERFACE:

The backp lane provides slots for four video A D

or

D/A cards and one Mux E ngine module. It is

designed to be configurable as either a video

transmitter as shown in Figure 3 or a video receiver

node

as

shown in Figure 4, with full duplex data

capability in either configuration.

DUPLEX DATA

4

v i w

T T L p n - m u xd a t ai t s

at 3 M H t

4iA

TX

P P

bit* at

100

K H t

TTL d.to

2

of

18

b i t s

at 26MHt

TTL data

18 bits at 26MH2

Fig. 3

Mult ip lexer conf igured

for

video t ransmit

111 244



VIDEO

Rx

DUPLEX DATA

wd.0

MUX

Fig.

4

Mul t ip lexer con f igured for v ideo receive

The backplanes are configured, by adding or

deleting video

A D

and D/A m odules,

to

transmit and

receive up to eighteen serial data channels at

25Mbit/s each. The combined digital video and data

bandwidth is equal to 450Mbit/s in both transmit and

receive directions.

The video in/out is ported to four

SMA

coaxial

connectors. TTL evel

data

is ported to one 40 pin

'data

in' connector, one 40-pin 'data-out' connector,

and one 26-pin connector for data associated with

pre-muxed data into video chan nels. One 25MH.z

ECL

clock

signal will

be

provided on each data

connector. The custom backplane is remotely

powered

so

the power supply module fimctions will

be moved

to

the backplane and a new power

connector will be

fitted

providing +/-5VDC power,

+/-5VDC sense, and ground.

4.4 VIDEO INTERFAC E:

At the ROV end, a remotely controllable

8

x 4

video routing switcher is required. A study was

conducted

to

determine if a comm ercial of€-the-shelf

unit that would

f i t

in the video canister was available.

Because only nineteen mch rack mounted switchers

were found, a switcher which meets the size

constraint is being custom designed. The switcher,

which

is

a wideband video solid state device, will

allow any fou r of eight Cameras to be switched to any

four of the video mux chann els. From the output of

the video switcher, four baseband video channels are

routed to the video m ux and ar e optically transmitted

to the video de-mux in the control console. This

arrangement will provide four simultaneous video

channels

to

the surface and a redundant route for

essential cam eras. At the console, the de-mux video

outputs are interfaced

to

a video routing switcher to

allow flexible video display configuration.

4.5 DATA MTERFA CE:

The fiber optic multiplexer provides a high

bandwidth, full duplex data capability.

The mux

engine transmits non return to zero

(NRZ)

optical

data at 500Mbit/s in both directions; 450Mbit/s of

usable bandwidth is digitized

video

and data, and the

remaining SOMbit/s is overh ead. Each video A D

and D/A module, which includes

two

stereo audio

and one data channel, contributes 100Mbit/s of

bandwidth. Since video is transmitted in one

direction only, all of the down link bandw idth is

dedicated to d ata.

The d ata interface module is designed

to

adapt to

the ROV sensor configuration. It c n accept RS-232,

RS-422,

FSK,

PWM, etc. and convert to TTL for

interface to the mux engine backplane. Future

growth capacity

is

provided with

10

bidirectional

serial channels available.

5.0

TETHER CABLE DESIGN:

The cable was designed in collaboration with

cable manufacturers who,

as

always, provided their

extensive know-how during the design process and

helped in making the design trade-off decisions. The

goal

of

the tether design

task was

to reduce the tether

diameter from 6 cm to 4.5 cm, while maintaining all

power and signal compa tibility with existing

ROV. Each power wire and signal element was

analyzed to assess their potential contribution to the

tether diameter reduction. Coppe r is the major

weight contributor in a cable, and because of the

requirement to m ake it neu trally buoyant in water, the

emphasis of the tether design consisted of reducing

the wire count.

5 POWER WIRE OPTIMIZATION:

Temperature rise tests on a similar cable were

performed to optimize the amoun t of copper required

to support ROV power loads.

As

a result of the

tests, the amount of copper was reduced by about

12%. The tests consisted of loading each power wire

with an electrical current equal to the actual ROV

In 245



load; the copper wire, insulation, and jacket

temperatures were monitored. Recorded

temperatures never exceeded 75 degrees C on the

winch drum operating in air.

5.2 SIGNALWIRE OPTIMIZATION:

A preliminary analysis of the system showed that

to significantly reduce the tethe r diameter, fiber

optics would have to be used to replace heavy

shielded balanced cables. Using optical fiber further

compounded the cable diameter decrease by

eliminating the need for shielding, whlch is a

significant contrib utor to th e cab le weight and overall

diameter. Trade-off studies determined that furthe r

reduction beyond the target diameter yielded

diminishing returns.

5.3 FIBER PACKAGING

Loose stainless steel tubes,

as

well as semi-loose

plastic tubes, were considered

as

candidates for the

tether fiber packaging. The semi-loose package was

selected because it made the fiber mechanical

termination easier in the field where tooling is not

always available. The loose stainless

steel

tube,

although an otherwise excellent choice for

oceano graphic cables, required a m ore complex

mechanical termination and was therefore not

selected. Five fibers were located in the center

of

the

tether cable, each one packaged in a plastic tub e and

covered with an overall jacke t. 100 KPSI tensile

proof-tested fibers were selected for compatibility

with the tether mechanical design.

5.4 TETHER CABLE M ECHANICAL DESIGN:

The tether mechanical requirements were

as

follows:

working load

O k N

bending diam eter 48cm under w orking load

a 2000 minimum bend over sheave cycle life

maximum elongation 0.5 under working

a 4ON/lOOm positive buoyancy a t depth

Ambient temperature of 38 degree C under the

electrical load in air and w ith

two

wraps on the

drum.

under working load

load

A tether will be type tested to veri@ that the

design meets the above requireme nts. Tests

conducted on a similar cable showed that the cable

elongation is under the pred icted elongation of 0.5

at 1OkN oad. The bend over sheave cycle life (2000

cycles) was better

th n

predicted. A temperature rise

test conducted on that cable revealed that wth n the

same jacketing material (Therm0 Plastic Rubber

TPR) heat deformation varies greatly from type to

type. A buoyancy

test

showed

th t

the cable

compresses due to air voids,

making

it negatively

buoyant at depth.

As

a result of

that

test, additional

buoyancy was incorporated by the cable designer to

compe nsate for pressure induced buoyancy losses.

5.5 TETHER CABLE MECHANICAL

TERMINATION:

The working load of the tether is transmitted to

the structure at both ends using meshed cable grips

over the outer floatation jacket; the cable grip

transmits the load progressively

to

the tether Kevlar

strength member via the jacket which is then under

shear stress. Conce rns over this method of load

transfer were mitigated through a series of tests,

which showed the need for multiple clamp

arrangem ent over the end of the cab le grip.

5.6 TETHER ELECTRO-OPTICAL

TERMINATION:

The tether cable will be initially terminated with

separate electrical and optical connectors. An

oil

filled, pressure compensated junction box will

provide a breakout area

to

separa te fiber from copper

wire, and provide space for service loop and splices

to connect the bare fiber to an armored wet connector

lead. Minimum bending radius for service loops

in

the junction boxes were calculated based on guidlines

provided by the fiber manufacturer below.

.The telecommunications industry rule of

thumb

for

long term reliability is to keep maximum stress on

fiber at 1/3 proof test level. For short term purposes,

stress should be kept a t 2/3 the proo f test level [3]

This junction box is a prototype connection used

to demon strate the upgraded system. It will allow

repairs while prototyping and provide empirical

data

on the behavior of the optical fiber.

This

will assist

in finalizing the design of a hybrid molded electro-

optical connector. Futu re development will consist of

designing a field installable electro-optical hybrid

connector to simplify tether changes.

III-246



The requirements for that connec tor are:

optical loss of 0.5 dB

maximum

100

matdunmate cycles

wated oil resistant

full

depth open f cepressure proof

for

bulkhead

and cable plug connectors

tether cab le elongation compatibility

suitable for field installation

CONCLUSIONS:

The integration a single fiber, full duplex,

5OOMbit.k telemetry system will enhance the

performance o f an existing ROV system by allowing

data

rates

not otherwise feasible. Benefits are

especially valuable in video performance, since up to

four real time video signals c n now be transmitted.

Using optical fibers in the tether and umb ilical cables

help reduce the diameter

as

well

as

the procurement

costs. A reduced cable diameter helps increase the

overall performance of the ROV system including;

ROV dynamic performance, tether management

reeling capabilities, and shipboard umbilical winch

reeling capabilities.

ACKNOWLEDGMENTS

We would like

to th nk

the following people for their

assistance with the integration of

t h i s

fiber optic

telemetry system:

Joseph Svacek, Ipitek, for his tireless applications

guidance, and innovation in the program .

John Purdy, Focal Technologies, for efforts in the

area

of

improved

FORJ

nsertion loss.

Gary

S.

Duck, JDS FITEL, for his assistance with

optical issuess.

Vincent Martinelli, Coming Incorporated, for

his

applications assistance with optical fiber.

Cal Peters, Consolidated Products Corporation and

Matt Badziony,

BIW

Cables Systems, for their

assistancewt the tether design.

REFERENCES:

[

1 Palais, Joseph C. Fiber Optic

Communications , 3rd edition,

New Jersey, Prentice-Hall, Inc., 1992

Principles Intervention 92 tutorial.

Intervention '92, San Diego, Ca.

Bending performance of m ultimode fiber

Coming Incorporated,

1992

[4] Pellen, Alain T. Power E lectronics Issues in

ROV s, Intervention 92, SanDiego, Ca.

[2] Brininstool, Michael R. Fiber Optic Design

[3] Martinelli, Vincent P. Applications D ata on

111-247

[doi 10.1109%2foceans.1993.326194] forst, v.j.; pellen, a.t. -- [ieee oceans '93 - victoria,...

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