NBSIR 73-341

TEST RESULTS FOR THE MOORING LINE DATA LINE

Doyle A. Ellerbruch

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

October 1973

Final Report

Prepared for:

National Data Buoy Office

National Oceanic and Atmospheric Administration
I
NBSIR 73-341

TEST RESULTS FOR THE MOORING LINE DATA LINE

Doyle A. Ellerbruch

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

October 1973

Final Report

Prepared for:

National Data Buoy Office

National Oceanic and Atmospheric Administration

a•

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W Roberts Director

CONTENTS

Page

1.0 INTRODUCTION 1

j 2.0 DEPLOYMENT CONFIGURATIONS 2

2.1 USCGC Acushnet Experiments 2 2.2 Environmental Buoy Experiments 2

2.3 AUTEC Experiments 3

2.3.1 Horizontal Deployment 3

2.3.2 Vertical Deployment 4

3.0 TIME DOMAIN DATA 4

3.1 Evaluation o£ the Ground Planes 5

j 3.2 Characteristic Impedance 5

j 3.3 Velocity o£ Propagation 5

] 3.4 Discontinuity and Coupler Locations 6

1 4.0 FREQUENCY DOMAIN DATA 6

: 4.1 Results at Test Frequency 7200 Hz 6

4.1.1 MLDL Parameters and Transmission

Characteristics 6

I 4.1.2 Current Standing Wave Pattern 7

j 4.2 Results as a Function o£ Frequency 8

4.2.1 MLDL Parameters and Transmission

Characteristics 8

4.2.2 Voltage Characteristics at the Input

to the MLDL 9

1 4.3.3 Wire-to-Wire Coupling 9

5.0 CONCLUSIONS 9

j 6.0 ACKNOWLEDGMENT 10

:! 7.0 REFERENCES . 11

i

iii
LIST OF FIGURES

Figure 1. Ground Plane Resistance

Fi gure 2. Characteristic Impedance Magnitude

Figure 3. Velocities of Propagation

Figure 4. MLDL Parameters

Figure 5 . MLDL DC and AC Resistance

r 1 gure 0 • LiOmpiex L.ndr a c u er 1 s L 1 c impeaance

Figure 7. Complex Propagation Constant

Figure 8 . Input Impedance with Short Circuit Termination

Figure 9 . MLDL Input Current versus Sensor Deck Unit Tap

Figure 10.

Figure 11.

Figure 12.

Figure 13.

Figure 14.

Figure 15.

Figure 16

.

Figure 17.

Figure 18.

Figure 19

.

Figure 20

.

Figure 21.

Number

MLDL Input Current versus Number o£ Strands in

Parallel

MLDL Input Current versus Coupler Locations

Coupler Voltage versus Sensor Deck Unit Tap

Number

Current Measured with Split Core Coupler

Current Measured with Solid Core Coupler

Coupler Voltage Measured with Split Core Coupler

Coupler Voltage Measured with Solid Core Coupler

Current versus Number of Strands in Vertical

Deployment

Current versus Sensor Deck Unit Tap Number in

Vertical Deployment

Characteristic Impedance Magnitude versus Frequency

Characteristic Impedance Phase Angle versus

Frequency

Series Resistance versus Frequency for 1-4 Strands

iv
LIST OF FIGURES Ccontinued)

Figure L L . Series Resistance versus Frequency for 5-8 Strands

r igure Lb . mauc Lance versus rrec{uency ror i 4

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r igure 9 /I inQuci.ance versus rrec[uency ror j o a tr anas

r igure Z D • L( Oil uu ct cine c verbub rrec{ueiicy xor i 4 o I. ranas

r Igure 7 A LiOnQucrance versus rrec^uency ror o o orranas

Figure 27. Capacitance versus Frequency

Figure 28. Input Impedance versus Frequency

Figure 29. Voltage at the Input

Figure 30 . Wire-to-Wire Coupling

V

TEST RESULTS FOR THE MOORING LINE DATA LINE

Results obtained from the Mooring-Line-Data-Line

(MLDL) measurements program are presented. Frequency

and time domain measurements were made to determine

characteristic impedance, input impedance, current, and

propagation parameters. Most of the measurements

were made with an MLDL deployed specifically for this

program, however some were made on an MLDL used to

moor a buoy.

Keywords: Characteristic impedance; coupler; current;

impedance; input impedance; mooring line data line;

propagation characteristics; transmission line.

1.0 INTRODUCTION

The measurement program developed to determine the electrical parameters of the Mooring-Line-Data-Line (MLDL) has

been completed. The work was performed by the Electromagnetics

Division of the National Bureau of Standards during 1972,

under NOAA sponsorship.

The MLDL is an eight-conductor woven harness, where each

conductor is encased in a polyethylene jacket and imbedded in

a synthetic fiber rope. The MLDL is approximately 550 meters

long.

Three separate series of experiments were conducted. The

first series was conducted aboard the US Coast Guard Cutter

Acushnet at Gulfport, Mississippi, April 10-11, 1972. The

objective was to check out test procedures that were being incorporated into the MLDL test plan [1], and to obtain data on

electrical ground planes planned for use on the deployed

buoys. Very short lengths (30 meters or less) of RG-8/U

coaxial cable, having its braided outer conductor stripped

away, were used to simulate the MLDL.

The second series was conducted aboard an Environmental

Buoy (EB-10) , June 23 , 1972 , one week after the buoy was deployed

in the Gulf of Mexico. The objective was to obtain data on the

MLDL in its deployed operational state. A special test plan

was developed for these experiments [2].
The third series was conducted at the U.S. Navy's Atlantic

Undersea Test and Evaluation Center (AUTEC) , Andros Island,

Bahamas, September 8-14, 19 72, where an eight -conductor MLDL

was deployed specifically for the measurements program defined

in the test plan [1].

The results obtained from the experiments are summarized

here. The measurement objectives, procedures, resources, theory,

and data reduction methods are discussed in detail in the

test plan previously reported. Equations and computer programs

for calculating the propagation properties of the MLDL have

been reported separately [3].

Section 1 is the introduction, and section 2 describes the

MLDL deployment configurations.

Section 3 summarizes results obtained with the Time Domain

Reflectometer in evaluating the ground planes , in measuring the

characteristic impedance and the velocity of propagation, and in

locating line discontinuities such as couplers.

Section 4 summarizes results obtained at discrete frequencies in determining the propagation parameters, the current

standing wave pattern, and the wire-to-wire coupling.

2.0 DEPLOYMENT CONFIGURATIONS

2 . 1 USCGC Acushnet Experiments

These experiments were conducted from the fantail of the

Acushnet. RG-8/U coaxial cables with their outer shields removed were used as a single strand MLDL. Lengths of approximately 8, 16, and 32 meters were placed approximately horizontal

in sea water such that both the input and termination ends were

accessible at the surface.

2 . 2 Environmental Buoy Experiments

These experiments were conducted on the deck of EB-10

after it had been moored. The MLDL extended approximately vertically into the sea and was under considerable tension due to

the anchoring function of the MLDL. The manufactured length was

approximately 525 meters. The actual length when placed under

tension is unknown.

2
2 . 3 AUTEC Experiments

The experiments were conducted from a U.S. Navy barge.

The MLDL had a "dry" length of 547 meters (1795 feet). It was

deployed first in a horizontal position and finally in a vertical position for testing at sea.

2.3.1 Horizontal Deployment

The barge was anchored in water that was at least 18

meters (60 feet) deep. A small buoy was anchored approximately

600 meters away. The deployed MLDL extended from the deck of

the barge to the buoy. Approximately 535 meters (1750

feet) of the MLDL was under water. The MLDL was supported

horizontally 9 meters (30 feet) below the surface by a series

of synthetic fiber guylines attached to floats. A guyline was

attached every 6 meters (20 feet) along the entire length of

the MLDL.

The input end of the MLDL extended through approximately

18 meters (60 feet) of 7.6 cm (3 inches) diameter flexible

metallic tubing. The tubing had two purposes. First,

it formed a coaxial outer conductor for the portion of the MLDL

that extended from the water surface up to the instrumentation

on the deck of the barge. Second, approximately 6 meters (20

feet) of the flexible tubing extended below the waters surface

and was used as the electrical ground plane at the input end.

The termination end was underwater but could be retrieved,

when required, from the anchored buoy.

The electrical conductor in each strand was individually

connected to terminal blocks at both the input and the termination ends. A shorting bus was used to connect all the electrical conductors together at the termination end. The bused

terminations were connected coaxially to a cylindrical galvanized metal ground plane that was 20 cm (8 inches) in diameter

and 2.25 (7 feet) long.

No Ocean Sensor Housings were attached to the MLDL when

it was deployed horizontally.

3
2.3.2 Vertical Deployment

The barge was towed into water that was at least 600 meters

(2000 feet) deep. The barge was held in a "zero-drift" position with a powered craft.

The deployed MLDL extended vertically into the water from

the deck of the barge. The flexible metallic tubing arrangement

at the input to the MLDL used in the horizontal deployment was

also used in the vertical deployment.

The cylindrical ground plane at the termination end was

loaded with anchor chain to keep the MLDL in a nearly vertical

position while deployed.

Two Ocean Sensor Housings were attached to the MLDL. One

contained a split-core coupler and was attached 305 meters

(1000 feet) from the input end. The other contained a solidcore coupler and was attached 518 meters (1700 feet) from the

input end. Both Ocean Sensor Housings were attached during

all the measurements with the vertically deployed MLDL.

3.0 TIME DOMAIN DATA

A Time Domain Ref lectometer (TDR) was used to accomplish

several objectives in this measurement program. The performance of the TDR and the data obtained with it were, to a large extent, as anticipated.

TDR measurements are especially useful in non-dispersive

networks which have single mode propagation. Unfortunately,

seawater is a dispersive electromagnetic medium in that its

attenuation constant is a function of frequency and its phase

constant is not proportional to frequency. However, it was

learned from the Acushnet measurements that the electrical

characteristics of seawater would not seriously degrade the usefulness of the TDR in evaluating MLDL termination ground planes,

uniformity of parameters, and continuity checks

EB-10 and AUTEC data were collected as a function of the

number of strands driven in parallel. Those strands not in

use were individually terminated in their characteristic impedance at the input end.

4
3.1 Evaluation of the Ground Planes

The objectives o£ these measurements were to characterize

the ground planes in terms of size, geometry, and resistance

at the metallic conductor-seawater interface.

The termination resistance values were obtained by analyzing the responses of the TDR with respect to selected termination resistances. An open-circuit termination was

accomplished by lifting the ground plane out of the water.

Ground planes of various geometries, sizes and materials

were measured. A summary of the results is given on Figure 1.

3.2 Characteristic Impedance

The objective of these measurements was to determine the

characteristic impedance of the MLDL. Impedance magnitude

values were obtained by analyzing the responses of the TDR

with respect to the responses obtained with selected termination resistances.

A summary of results are given in Figure 2. The measured

values obtained on EB-10 are significantly higher, probably

because the MLDL was under tension. It is probable that the

cross-section dimensions of the line changes under tension by

an amount necessary to produce the measured differences. For

example, the helically wound center conductor will tend to

straighten under tension, resulting in a smaller effective inner

conductor diameter. Further, the synthetic fibers may not be

water saturated under tension, resulting in a larger effective

outer conductor diameter. Either of these effects would tend to

produce a higher characteristic impedance when the MLDL is placed

under tension.

Not shown on Figure 2 is the characteristic impedance of

the single strand RG-8/U lines. Their measured value, = 95.2 ohms, is significantly different than that obtained with

the MLDL because materials and cross -sect ional dimensions are

different

3 . 3 Velocity of Propagation

The objective was to determine the velocity of propagation of a signal on the MLDL. The results were obtained as the ratio of twice the MLDL "dry" length to the total propagation time measured with the TDR.
A summary o£ the results are tabulated on Figure 3. The

measured value obtained on EB-10 is higher than that obtained

with the vertically deployed MLDL at AUTEC. Changes in the

physical dimensions as discussed in section 3.2 would be directly applicable here also. It should be noted, however, that

the actual length o£ the EB-10 MLDL is not known. Further, it

was assumed that the length of the AUTEC MLDL remained at 547

meters when deployed vertically.

3 . 4 Discontinuity and Coupler Locations

The objectives of these measurements was to determine if

the TDR has sufficient sensitivity to detect a discontinuity

in the electrical parameters of the MLDL. During the horizontal deployment experiments at AUTEC the MLDL was lifted out

of the water at a point 250 meters from the input end to form

a discontinuity. During the vertical deployment the Ocean

Sensor Housings with couplers installed were considered as discontinuities. Even though these discontinuities were not

detected with the TDR, it is believed that discontinuities as gross as a metallic conductor break would be detectable because

large changes in the characteristic impedance will occur when

the number of conductors in parallel changes as shown on

Figures 1 and 2.

4.0 FREQUENCY DOMAIN DATA

4 . 1 Results at Test Frequency 7200 Hz

4.1.1 MLDL Parameters and Transmission Characteristics

The objectives in these measurements was to determine

values for the four fundamental line parameters; self-inductance L, wire- t o- seawater capacitance C, series resistance R,

and shunt conductance G, and to determine the characteristic

impedance , the complex propagation constant, and the input

impedance when the MLDL is terminated in a short circuit.

6
Test data consisted of complex input impedance measurements when the MLDL was terminated first in a short-circuit

and later in an open-circuit. The physical "dry" length of

the MLDL was used in data reduction by assuming that its "wet"

and "dry" lengths were identical.

Results derived from the test data are given in Figures

4 to 8 . Figure 5 is a comparison of the resistance data obtained

at dc and 7200 Hz. The dc values were obtained by measuring

the resistance of the metallic conductors only and does not,

therefore, include the resistance of the seawater.

4.1.2 Current Standing Wave Pattern

The objective of these measurements was to determine the

current standing wave pattern with the MLDL operated at its

anticipated operational current input (1 ampere) and terminated

in a short circuit.

Current data were obtained for both horizontal and vertical

deployments. In the horizontal deployment a coupler was moved

from the termination end to the input end of the MLDL in increments

of 15 meters. An ac voltage was measured at the terminals of a 12 -turn secondary transformer in the coupler. A coupler rectified current output was also measured by connecting a full wave

bridge rectifier, having a 144 ohm load resistance, to the

secondary terminals

In the vertical deployment the couplers mounted with Ocean

Sensor Housings were used. Each Ocean Sensor Housing contained

a full wave bridge rectifier having a 144-ohm load resistor,

and a battery-powered strip chart recorder.

The Sensor Deck Unit (SDU) power amplifier used to supply

current to the input to the MLDL was evaluated. Data on SDU

performance were obtained for both deployments. The objective

was to determine how the SDU should be adjusted so that it would

deliver 1 ampere at the input of the MLDL during subsequent current standing wave measurements. Variables in these experiments

were the number of MLDL strands driven, the position of a coupler

on the MLDL, and the SDU output tap number. Results are given

in Figures 9 through 12. The apparent input current steps observed in Figure 11 resulted from the resolution of the current

meter used in the experiments.

7
Figures 13 and 14 are the current standing wave patterns

obtained with the split core and the solid core couplers used in

these experiments. A single current value obtained with eight

strands in parallel in the vertical deployment is also shown on

Figures 13 and 14.

Figures 15 and 16 are the coupler secondary rms voltage

values

Data obtained with the MLDL deployed vertically are given

in Figures 17 and 18.

Two experiments were tried to determine if the seawater within the coupler forms a short circuited secondary

turn. In one experiment the split core coupler was installed

305 meters from the input end. Eight strands were driven in

parallel which, for a 1.10 ampere input current, resulted in

17 vac rms across the secondary terminals, and 108 ma rectified

current. The diameter of the MLDL at that point was then built

to the inner diameter of the coupler with 15 cm wide synthetic

fiber tape in an attempt to keep the seawater from entering

the volume between the MLDL and the coupler. Eight strands

were again driven in parallel. The input current and secondary

voltage remained the same, however the rectified current increased to 109 ma. It was the general consensus of those

present that this attempt to keep seawater out of the coupler

was not entirely successful.

The second experiment was done with the split core coupler

153 meters from the input. With the seawater in the coupler

and eight strands connected in parallel the input current was

1.06 amperes, 14.0 vac rms was measured across the secondary

and the rectified current output was 86 ma. The coupler was

then lifted above the water surface. The input current remained constant while the secondary voltage dropped to 13.5

vac and the rectified current dropped to 82 ma.

4 . 2 Results as a Function of Frequency

4.2.1 MLDL Parameters and Transmission Characteristics

The objectives in these measurements was to determine

values for line parameters, the characteristic impedance, the

propagation constant, and the input impedance as a function

of frequency when the MLDL is terminated in a short circuit.

8
Results derived from the test data are given in Figures

19 through 28. The parameters are calculated for frequencies

from 5 kHz to 20 kHz.

4.2.2 Voltage Characteristics at the Input to the MLDL

The objective was to measure the magnitude of the voltage

at the input of the MLDL as a function of frequency to determine the frequency at which it is one -quarter wavelength long.

Data obtained from these measurements is shown in Figure 29

The peak of the curve occurs at the frequency where the line

is one-quarter wavelength long, which is 27.6 kHz.

4.3.3 Wire-to-Wire Coupling

The objective of this measurement was to determine the

wire-to-wire coupling between the center conductors of the

MLDL. The power coupled from the driven to the undriven

strands was measured. The coupling data derived from those

measurements is given in Figure 30.

5.0 CONCLUSIONS

The objectives for the testing program were:

Task 1. Develop test plans and procedures for in situ

testing of the Engineering Evaluation Platform

Moor ing- Line -Data -Line

Task 2. Perform the in situ testing in accordance with

the developed test plan.

Task 3. Perform auxiliary tests in situ or in the laboratory as required to meet the requirements of the

test program.

The test plan and procedures were completed in May 1972.

Measurements conducted aboard the US Coast Guard Cutter Acushnet

and in the laboratory at Boulder, Colorado, were conducted prior

to finalizing the test plans and procedures.

9
In situ testing o£ the eight-conductor MLDL was accomplished

aboard the Environmental Buoy (EB-10), June 1972, and at the

Atlantic Undersea Test and Evaluation Center (AUTEC) , September

1972 . Data were obtained with measuring systems in the time domain

and in the frequency domain.

The material and shape of the ground planes were found to be

non-critical to the performance of the MLDL. A galvanized steelseawater contact area of one square meter or larger is sufficient

to provide a termination impedance less than one ohm.

The current standing-wave pattern was measured at the NOAA

proposed operational frequency 7200 Hz. The pattern was determined

to be a very smooth function along the MLDL, but sensitive to

the number of strands driven in parallel.

The electrical characteristics of the MLDL were determined

to be a function of the number of conductors driven in parallel.

The characteristics become increasingly difficult to measure

as the number of driven strands is increased, and as the frequency is increased.

6.0 ACKNOWLEDGMENTS

Many individuals are responsible for the success of this

measurements program. Particular acknowledgments are made to

Mr. Richard P. Mueller, Sperry Rand, Mr. William Rehman,

General Electric, and the range staff at AUTEC.

10
7.0 REFERENCES

[1] Test Plan and Test Procedures for the National Data Buoy

Project Mooring-Line-Data-Line (MLDL) , by D.A. Ellerbruch,

submitted to the National Data Buoy Office, May, 19 72

(unpublished)

[2] Test Plan and Test Procedures for the National Data Buoy

Project Mooring-Line-Data-Line (MLDL), OPS-1, (EB-10), by

D.A. Ellerbruch, submitted to the National Data Buoy Office,

June, 1972 (unpublished).

[3] Single Strand Model Computer Programs for the Transmission

Line Properties of the Mooring Line Data Line, by D.R.

Holt and N.S. Nahman, April, 1973 (unpublished).

[4] MLDL Measurements on the Acushnet in April, by D.A.

Ellerbruch, letter report submitted to the National Data

Buoy Office, April 27, 19 72 (unpublished).

[5] MLDL Measurements on EB-10, by D.A. Ellerbruch, letter

report submitted to the National Data Buoy Office,

July 25, 1972 (unpublished).

11
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5 10 15

FREQUENCY - KHz

22. Series Resistance versus Frequency for 5-8 Strands

-33-
000L/AyN3H0y3IW - HDNViOnaNI
100

80

60

40

20 -

O

O

o

A

O

O

STRANDS DRIVEN

O 5 A 6

7 O 8

O

10 15

FREQUENCY - KHz

O

300

250

200

1 50

1 00

50

o

o

o

o

o

LlJ o

o

Q

20

Figure 24 . Inductance versus Frequency for 5-8 Strands

-35-
14

o

o

C/5 o

UJo

H-O

=)

o

o

C_)

1 2

10

2 -

STRANDS DRIVEN

O 1 A 2

3

O 4

Q

A

O

A

O

1 0

FREQUENCY

1 5

KHz

A -

20

Figure 25. Conductance versus Frequency for 1-4 Strands

-36-
13

12

11

10

9

8

7

6

5

4

3

2

1

0

CONDUCTORS DRIVEN

O 5

A 6

7 O 8

s

- 40

30

20

10

20

Figure 26. Conductance versus Frequency for 5-8 Strands

-37-

30 -

20 -

10 -

0

10 15 20

lOOi50 -

ONE STRAND

SHORT CIRCUIT TERMINATION

MLDL HORIZONTAL

MLDL VERTICAL

• EB-10

J L

10 1 5 FREQUENCY - KHz

20

Figure 28. Input Impedance versus Frequency

-39-
FREQUENCY (KHz)

Figure 29. Voltage at the Input

-40-
FREQUENCY - KHz

Figure 30. Wire-to-Wire Coupling

-41-
FORM NBS-114A (1-71) U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA ^ ^^^^ ^3 3^^

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Test Results for the Mooring Line Data Line

5. Publication Date October 1973

6. Performing Organization Code

7. AUTHOR(S)

D. EUerbruch

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS

MAT* T/^KT AT DITDCATT (~\ IS QT A Mr\ A D r\C "D y-vii T Vx INAIIUINAL tJUKnAU Ur ol AiNU AKUo , xjOUiClGi J_j3,DS.

DEPARTMENT OF COMMERCE

Boulder, CO 80302

10. Project/Task/Work Unit No. 2724464

11. Contract/Grant No.

12. Sponsoring Organization Name and Address National Data Processing

NOAA

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) Results obtained from the Mooring-Line-Data-Line (MLDL) measurements

program are presented. Frequency and time domain measurements are made to

determine characteristics impedance, input impedance, current, and

propagation parameters. Most of the measurements were made with an MLDL

deployed specifically for this program, however, some were made on an MLDL

deployed buoy.

17. KEY WORDS (Alphabetical order, separated by semicolons) Characteristic impedance; COUpler;

current; impedance, input impedance; mooring line data line; propagation

characteristics; transmission line.

18. AVAILABILITY STATEMENT 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

^UNLIMITED.

UNCL ASSIFIED

1 1 FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

USCOMM-DC 66244.P71

USCOMM - ERL