2 1, ME 1973
A-1 'lute
C 0 P /
i.1 N (--, ..'1 ', LI . i li.,.41 '
k..::: iil 4 ti cdLab. v.
ScheepshouwLmilr-kTechnische Hogaschool
Delft
Design Summary Of The
r
P reP t?;.,i vit t4414 1-7 7,-;)p
-Prepared For The
16th AvtriErio-4,,,IN
40.e. . ;71o'qu
77,
/AMA, LA)M-LKraN
SAO PAULO, BRAZIL
9-13 August 1971
By
Ernest A. Laufer
AM CORPORATION
Bruce Johnson
U.S. NAVAL ACADEMY
U.S. NAVAL ACADEMY
DIVISION OF ENGINEERING & WEAPONS
Annapolis, Maryland
L74-3 (.ff (771 r dREPORT E-71-3
DATUMz34"63
Biblic.theek van trieEpvaarfnee e D Clii.'1ENTAI ::ACKNOCILEDGEI,ENTS
The authors wish to acknowledge the support of Code 034.12B of the Naval Ship Systems Command in funding the publication costs and Dr. Johnson's salary during the preparation of this report. In addition, we would like to thank Messrs. Louis Schaffer, Norman Nogic, and William Brustad of the AAI Corporation for their imaginative contributions to the design of the system.
Finally, we wish to thank Mr. Charles Summers of the Chesapeake Division, Naval Facilities Engineering Command, who as the Officer in Charge was instrumental in providing for the dissimination of information among the
TABLE OF CONTENTS
PACE NO.
INTRODUCTION
NEW INSTRUMENTATION BEING EVALUATED BEFORE
COMPLETION OF THE 380 FOOT TANK 3
8-Channel Data Acquisition System for Steady
State Data 3
Time Data 100 Digital Time Series Analyzer 3
PDP 15/40 Data Acquisition and Analysis System 4
INVESTIGATION OF DATA TRANSMISSION AND POWER
DISTRIBUTION SYSTEMS FOR THE USNA 380 FOOT TANK 6
Objectives 6
Requirements 8
Data Transmission Systems Investigated 12
Control Signals 18
Power Distribution System 20
Electromagnetic Interference 23 Selected System 26 A. B.
A.
C. D. E: F. G.INTRODUCTION
In order to efficiently utilize the new 380 foot towing tank presently under construction at the U. S. Naval Academy, considerable study has gone into making the transfer of data from the sensor to the computer printout an efficient and interactive process. This has involved trying out new
computer equipment and techniques on the present 85 foot towing tank, as well as design studies for the data transmission and power distribution systems
for the new tank. This report summarizes these dual efforts.
The 380 foot towing tank physical facility is described in greater detail in Report 71-2*entitled Design Summary of the 380 Foot High Performance
Towing Tank. A plan view of this overall facility is also shown in Figure 1.
The design studies, which are the subject of this report, were undertaken by AAI Corporation of Baltimore, Maryland under the supervision of the Engineering Division of the U. S. Naval Academy at Annapolis, Maryland and under contract with the Chesapeake Division of the Naval Facilities Engineering Command.
The data acquisition and power distribution systems, unlike the data analysis equipment, are dependent on the particular configuration evolved for
the towing tank and the associated carriages. Consequently the discussion
is
divided into two parts; Part I discusses the analysis systems contemplated forprocessing the data; Part II describes the means of getting the data to the analysis equipment as well as the implements for providing power to the instru-mentation and its control.
*Reference 4
RESTRICTED ACCESS TO SERVICE PLATFORM DOWN TO ELEV +2.50 FOUNDATIONS ELEV 9' ELEV -7.00 TANK 3L9E2NGTH
9:14
41
...e..
,..:ct
oi
6*
'N"
0OWN
TOillfrELEV0.0E0LEV
+7.00 ELEV -11.00' 0.0.100°.°1tie
411k C
1
11*°.°"e.
PLATFORM ELEV 7.00' N...11 000. LEV E1.90E0AM ELEV +9.00 BEAM ELEV +9.00 DOWN TO ELEV 0.00 PLATFORM ELEV 9.-4" ELEV 11RESTRICTED ACCESS TO SERVICE PLATFORM
DOWN TO, ELEV +2.50
FIGURE 1 FACILITY LAYOUT ELEV +5.50 ELEV +5.00 ELEV +7.00
-3
I. NEW INSTRUMENTATION BEING EVALUATED BEFORE COMPLETION OF THE 380 FOOT TANK
8-Channel Data Acquisition System for Steady State Data
An 8-channel data acquisition system, supplied by Spiras Systems of Waltham, Massachusetts, has been in use in the present tank for two years. This system is essentially a multi-channel integrating digital voltmeter with a common time-base and a teletype output. By using the voltage-to-frequency converter and counter combination, very accurate mean values can be obtained from sensor data which may contain considerable noise from carriage vibrations. No other statistical data such as variance can be computed, however, so the
system is limited to steady state runs. At present, the same teletype is used as a time-shared terminal for the Naval Academy's Honeywell 625 computer, but this involves switching the teletype connections from the data acquisition system to an acoustic coupler for the computer link. A paper tape is punched during the data runs and then read into time-shared computer files. Midshipmen and faculty may analyze the data from any of the 125 teleprinter terminals located throughout the campus.
Time Data 100 Digital Time Series Analyzer
A two-channel, digital time series analyzer has been in operation for a year and half and is located in a room adjacent to the present, 85 foot
towing tank. This analyzer has various algorithms such as Direct and Inverse
Fourier Transforms, Auto and Cross Spectrum, and Auto and Cross Correlation permanently wired into the system and can operate in "real time" with data
the outputs of wave gages, accelerometers, and hot-film anemometers.
Although
the analyzer can be operated on-line with analog data transmitted directly
from
the sensors via coaxial cables, this mode of operation is only used to demonstrate real time operation or to make interactive adjustments in the experimental
set up. In the present configuration of this data acquisition system, the
incoming data is lost, once it is analyzed, and is not available for further
processing. Consequently, most of the data is presently recorded on FM analog
tape for permanent storage, and is then analyzed at a later time. Improvements
in the system, discussed next, will enable the data to be analyzed in real time while simultaneously being stored in digital form by an additional computer.
C. PDP 15/40 Data Acquisition and Analysis System
The Naval Academy has under procurement a laboratory data acqui-sition and analysis system. It will consist of a PDP 15/40
computer with 24,000 words of core, dual disks, dual magnetic DEC tapes, A to D converters and a "Real Time Executive" software system.
This system will be located in the same room as the Time Data 100, next to the present 85 foot towing tank, and will be interfaced to the Time Data Analyzer, as well as having its own analog to digital conversion capabilities. Towing tank data will be digitized
"on line" through patch
panel
connections, accepted from the present8-channel
data acquisition system and stored either on one of the disks or on DEC tape, depending on the application. The data can be analyzed using special
software
developed for the PDP 15 or it can be transferred to the Time Data 100 if
one
of the permanently resident algorithms is needed in the analysis.
The analyzed
output can be viewed on a CRT display, plotted on an X-Y Recorder or printed
on a Typagraph terminal, or printed and plotted on a high speed printer/plotter at 4800 lines per minute. It is hoped that enough experience with this system can be gained between now and the time the 380 foot towing tank is completed to make the operation of the new tank quite efficient from the beginning.
INVESTIGATION OF DATA TRANSMISSION AND POWER DISTRIBUTION SYSTEMS
FOR THE USNA 380 FOOT TANK
A. Objectives
The USNA towing tank is designed to accommodate two towing
carriages. One a small lightweight unmanned "High Speed" (up to 50 feet per
second) carriage; the other a heavier, "Low Speed" (up to 25 feet per second)
carriage capable of carrying an operator, on-board instrumentation, and an entire class of Midshipmen. The optimum propulsion system for this two
carriage configuration, was found to be a dual cable power drive for the high speed carriage and the use of the high speed carriage to tow the low speed carriage when the low speed carriage is in use. The objectives of these
studies were to establish feasible parameters and requirements for a number of electrical interfaces between the carriage and the shore.
Obtaining analog data from the high speed carriage model.
Providing power to the high speed carriage instrumentation.
Transmitting television pictures from either carriage. Providing interlocks to determine the condition of the high
speed carriage and whether it is coupled to the low speed
carriage and thus setting automatic speed and acceleration limits in the propulsion system.
Enabling control functions on the unmanned carriage to be carried out from the control room ashore.
Making it possible for an operator in the control room of the low speed carriage, when it is coupled co the high speed carriage, to exercise speed control and many other functions
from his control panel.
Supplying sufficient power aboard the low speed carriage to operate on-board instrumentation and air-conditioning for the
cab.
6
The parameters taken into consideration include the dynamic range,
both amplitude and frequency, power level, impedance, etc. of all the items to be processed between the shore and the carriage. Another aspect of the problem peculiar to the USNA facility is the interference to be expected from the US Naval Radio Station in addition to the other interference sources within
the building.
Several generic subsystems were reviewed for their applicability and cost effectiveness in mechanizing one or more of the functional interfaces
for this application and the recommended system was evolved. These concepts
include:
For Analog Model Data and T.V. Tape Recorder
Laser Telemetry Microwave Telemetry Trailing Wire Cable
For Control Signals - Bidirectional link required Laser Telemetry
Microwave Telemetry Trailing Wire Cable
Frequency Shift Keyed Tone Oscillators Serial Digital Data Link
For Carriage Power
On Board Batteries Trailing Cable
Power Rail
It can be seen that the need for an integrated system will have an effect on the choice of subsystem for a specific function.
B. Requirements Summary
The requirements for transmission of data, remote control functions and carriage power are summarized on the chart on the following page.
Analog Data Channels
The most demanding instrument used as reference for analog channel data system design, was the Constant Temperature Anemometer System, Model 1050 made by Thermo Systems, Inc., St. Paul, Minnesota. The output
from the system, when used with the recommended Linearizer, is 0 to 10 volts DC with significant turbulence information down to a few millivolts.
Fre-quency response of the electronics is DC to 200 Khz. Output impedance of the Linearizer Module is 20 ohms for driving the data transmission system. If
the Signal Conditioner Module is used in place of the Linear izer, the output
is still 20 ohms but the range is 0 to 15 volts.
Direct output from the Anemometer Module is 0 to 20 volts DC at a 50 ohm impedance. Output noise level is .02% over the frequency band, for a dynamic range of 74 db. If the data is to be processed in a digital computer, it will be possible to perform signal conditioning, linearizing, etc. on the digital data and use the Anemometer Module output without the additional signal processing on the carriage. Line driver
amplifiers to reduce the impedance to 5 ohms or less will still be desireable with the proposed cable system. This will reduce the effect of induced noise
8
2.
TABLE 1. ELECTRICAL INTERFACE REQUIREMENTS
Item Requirement .Specification
1 8 Analog Channels ' 60 db dynamic range re: 10 volts
0 to 20 Khz frequency
2 1 TV Channel DC to 16 1,111z frequency
75 ohms 40 db signal to RN'S noise
3 13 High Speed Carriage Remote Relay closure within 0.1 second of
Control Channels remote switch activation.
4 Interlocks Denoting 6 ON-OFF Signals 10 hz,
Carriage Condition 10 db Signal to Noise
5 Low Speed Carriage Numeric Logic outputs in BCD Form. Similar
Speed Readout - (4 Digits) to Item 4.
6 Low Speed Carriage On-Board 16 ON-OFF Logic Bits
Speed Control 10 hz, 10 db signal to noise
7 Acceleration Control 1 Analog Channel, 10 hz
40 db dynamic range re: 10 volts
8 17 Low Speed Carriage Control Logic outputs activating lamp drivers -Panel Status Indicators similar to Item 4.
9 Control System Controls 7 ON-OFF logic bits within 0.1 second of control activation, 10 db signal
to noise
10 High Speed Carriage Power 208 volts 30 60 hz 2 KVA
11 Low Speed Carriage Power 208 volts 30 60 hz 20 KVA with growth potential to 40 KVA
12 Intercom
13 Emergency Stop
14 Safety Ground
Shore to carriage and carriage to shore 300 hz to 7 Khz less than 300 ohm
impedance.
Continuously available from both carriages when coupled and H.S. carriage when
un-coupled; instantaneous response.
All carriage metal parts must be main-tained grounded to avoid shock hazard to personnel and help with interference
Rrrsf'"'
voltages from other channels and other magnetically or capacitively coupled
noise.
The typical instrument to be used for acoustic noise and pressure measurements will be a hydrophone such as those made by Clevite Corporation and Atlantic Research. These units can be flush mounted on the model or at other locations in the towing tank. Response frequencies for
those piezoelectric units can be from 0.1 Hz to several hundred Kilohertz
for some models. A preamplifier is used with the instrument to convert the
signal to a level compatible with passing over a short length of cable to whatever method will be used to transmit the data. Dynamic range of the signal at the hydrophone can be as much as 100 db. The amplifier and
transmitting components will limit this capability.
3. Television Signal
There are a number of sources of equipment for closed circuit TV systems. These include Cohu, Lear Siegler, and MTI among a large number of suppliers. The standards for many of these systems are similar because they are based on the home TV set. The MTI Model VC-20, for example, seems particularly well suited for the towing tank application because it keeps the video level constant for a 4000 to 1 dynamic range of illumination. This makes it possible to have very low illumination and still monitor the
experiment. The desirability of low illumination is the reduction of algae
in the water and the reduced requirement of carriage power for flood lighting
the experiments. The output requires a channel capable of DC to 10 to 16 Nhz
bandwidth (depending on model selected) which can be transmitted by one of the
systems discussed below or a coaxial cable. The camera and its rack mounted control unit must be mounted on the carriage. A remote monitor at the
control console or video tape recorder can recover the pictures.
ON-OFF Signals
The general category of ON-OFF signals can be considered
as digital data. This type of signal is required in both directions, i.e.
shore to carriage and carriage to shore and for both carriage configurations. As shown in the summary, the signals that can be considered in this category are remote controls which close relays or light lights at the other end, as well as interlocks which signal conditions to other systems for automatic
action. More complicated signals such as the speed commands and the speed
readout on the carriage are also in the category of digital signals.
The system operating requirements dictate the digital data rates and an update rate of 10 times per second was selected as sufficient for the needs of the speed control system. The use of digital signals affords a measure of noise immunity in that the receiving circuits need only detect one of two conditions of the transmitted signal. A 10 db signal to noise ratio is therefore recommended as a readily achievable quality. The detailed system design includes parity bits in the data words, synchronization pulses and bandwidth discrimination of the data pulses for signal correlation thus making the false alarm rate in any 0.1 second interval extremely small.
Power Requirements
The power required for the carriages is based on estimates for equipment presently planned to be used on the carriages and possible
4,
future additions. Particularly the anticipated low speed carriage requirement
is based on estimates for similar applications.
6. Miscellaneous
The remaining items requiring electrical interface do not require elaboration; this includes the intercom, emergency stop, and safety
ground.
C. Data Transmission Systems Investigated
1. Microwave RF Systems
There are two basic methods of transferring the data channels between the carriage and the data processors, namely in Analog or in Digital
form. Both methods require one or more channels for transmission and the
fewer the transmission channels, the higher the bandwidth requirement because the data channels must be timed shared. Conversely, if more transmission channels are required, the probability of interference and complexity of equipment as well as costs increase.
To multiplex the 8 data channels on one serial digital data link requires a bandwidth of approximately 10 Mhz. This is based on 8 channels sampled 5 times per data cycle, having an upper limit of 20 Khz frequency response and a dynamic range of 60 db or eleven binary bits per sampled word. Some additional bits are required for word and frame synchronization, This
is compatible with the bandwidth requirement of the TV channel.
It is possible to multiplex the same 8 channels in analog form on 8 voltage controlled oscillators (VCO). Frequency spacing of the
77rwt.,-12
-oscillators must be compatible with a deviation of + 40 Khz to get adequate
resolution. Standard IRIG channels to handle this requirement are:
250 Khz
+ 40 Khz400
Khz +
40 Khz550 Khz
+ 40 Khz700 Khz
+
40 Khz
850 Khz
+ 40 Khz 1,000 Khz + 40 Khz1,150 Khz ± 40 Khz
3,300 Khz + 40 KhzThese 8 channels would be mixed on one RF transmitter with the bandwidth requirement for the transmitter channel approximately 5 Mhz. The VCO, however, is not capable of 60 db dynamic range. Forty db is the practical dynamic range for voltage controlled oscillators.
The most economical method for retrieving the 8 channels of analog data appears to be through the use of a trailing wire. A chart showing the relative cost of the different systems considered is presented
in Figure 2. The cost considerations are based on budgetary estimates from
potential suppliers of the equipment considered. These suppliers included: Voltage Controlled Oscilators
Microwave Transmitters & Receivers
Antennas
Slip Ring Assembly
Analog to Digital Converters
Digital to Analog Converters Multiplexers (Digital)
Analog Discriminator
13
Vidax
Electronic Development Corp. Teledyne Andrews Fabricast Bunker Ramo Analog Devices Analog Devices Analog Devices Vidar
Connectors Typical
C-8 Ide:t VCO 8 Ident A/D
Iv]
Ident A/D:Yr) t 8 Ident VCO kG0 '"Co 1A/DI 8 Ident A/D Multiplex Microwave rransmitter Multiplex Multi Multirle-111111 Wire in Tr I
Coax in Trough Wire in Trough
Coax in Trough Microwave Transmitter ( Ant tuna)
-S-
9
Antenna)
Antenna Transmitter GRDCoax Rotary Joint
Reel
Receiver
Coax
Rotary
Joie
Reel9 Wire it,cciver D/A 8 Pair Rtceivcr lip Ass Decomm Decomm eel 'Disc 8 'dent Disc Disc 8 Idlra Disc isc A 8 Ident D/A A 8 Ident D/A Connectors Cost Dollars 8 Typical 8 1,300 10,500 16,000 10,800 60 db Possible; High 11,500
Noise Immunity; Coax Only Required
17,000
Not Desirable Due to
3,100
High Data Rate
8,200
FIGURE 2. COST COMPARISON OF VARIOUS SYSTEMS
FOR 8 ANALOG DATA CHANNELS CARRIAGE TO SHORE TRANSMISSION
Comment
Eliminate Onboard Battery and Conversion; 60 db 20 KHZ No Problem Eliminate 8 Wire Pairs in Trough; 40 db at 20 KHZ Feasible Eliminate Wires; Need on Board Power; and Conversion.Has Multipath Problems 60 db Possible; ;high Noise Immunity 60 db Possible; No Wire6; Need On Board Power Not Desirable Due to High Data Rate
Coax in Trough 0 y o 8 Ass'y 0 Dec omm 4 Coax
Rotary Joint Reel
Table 2 gives estimated power consumption, size and weight for the on-board components when 2 RF links are used. An RF link for TV and another for data are required. This does not provide for control functions such as remote setting of amplifier gains on the carriage during a test run. This remote control would require a third RF link. Power must be carried aboard the carriage in the form of batteries both for the instrumentation and for
the RF equipment. This is an additional expense compared to a wire system
where power can be brought aboard on the same cable used for signals in both
directions.
Laser
The chart showing the options for data transmission can be used to evaluate a laser system by replacing the RF components on the carriage by a laser with an appropriate modulator, and by replacing the receiver by a
photomultiplier tube. When comparing the laser system to a trailing wire
system, the comments are the same as for the RF link; namely two way communi-cation is required if remote controls are desired, an alternate system of providing power is necessary, and the modulator-laser-photomultiplier combina-tion in addicombina-tion to the multiplexing and discriminacombina-tion systems will be much more expensive than the wire system.
On-Board Recorder
It will always be possible to supplement the data trans-mission system by use of an on-board instrumentation tape recorder. This is
not recommended as the primary means because the data is not available in real time when a tape recorder is used. The dynamic range of tape recording,
2
Fits in 19 inch (nominal)rack.
TABLE 2
CHARACTERISTICS OF ON-BOARD EQUIPMENT
Unit Weight (lbs) Power (watts) Height ' (inches) Width (inches) Depth inches Typical Manufacturerer 1.
TV System 1 ea Camera 1 ea Control Unit
3.5 14.5 40 2.75 5.25 2.75 * 19 9.75 13.75 MTI VC-20 2,
Flow Inst. 6 ea 1050 2 ea 1051-6 Pwr Unit
1058-12F Rack 1058-6 Rack 33 25.6 500 14.12 7.12 * 19
*
19 12.2 12.2Thermo System Inc.
3.
VCO 8 ea Modules 4 ea Misc. Modules
24 12 200 7
*
19 _ Vidar 4. Transmitter 2 ea 6 10 3 2 7 Teledyne 5. Antenna 2 ea 20 -Andrews 6.Misc. Lights Horn, etc.
50 800 -_ 7. Battery 50 -10.25 9.75 10 Gulton GB-22 8.
Power Converter & Battery Charger
30 -7 * 19 -*
typically used for telemetry and instrumentation is limited to 40-48 db because of the characteristics of the recording process. Frequency response
of 20 Khz, however, can be achieved by recording each analog channel on one track of the recorder. These recorders are normally available in 7 or 14 track configurations. VCO's are used in order to obtain the DC to 20 Khz response and the recorder and playback unit must be provided with the
appropriate electronics.
4. Trailing Wire
The use of a cable connection between the carriage and the data reduction instrumentation system will provide the capability for meeting
the dynamic range as well as the frequency response requirements of the analog
data channels. This is because time sharing is not required and the data can
be transmitted in parallel and in real time. The additional advantage of using a trailing cable for data transmission is that the TV system, power for the high speed carriage, and instrument control channels can be included in the same cable system with minimum additional complications. A cable data trans-mission system can protect the data channels from interference generated outside
the system as well as that possible between channels. The reduction in the complexity
of
the electronic components associated with a cable system versusany other data link, is yet another advantage enhancing the inherent relia-bility of the system. The previous chart (Figure 2) which presents the
economic comparison of the various systems indicates that potentially lower cost is another advantage of the trailing wire data transmission system.
There are, however, several potential problem areas in attempting to use a trailing wire in the towing tank application. First, the cable may have to be guided into a trough or other retention medium in order
to keep it from interfering with the carriage operation. Secondly, the most straightforward method of reeling the cable in and out necessitates the use of slip rings which have the potential of imposing electrical noise on the
transmission channels. To avoid the slip ring noise, a two brush or a four
brush per ring system can be provided. The combination of ring and brush materials has been selected to give minimum noise in the desired speed range. This is possible because of a long history of developments in the signal slip
ring art. It will also be possible to reduce the effect of slip ring noise
by operating a low impedance line at relatively high full scale voltages to keep the slip ring-generated noise to a low percentage of the total signal range.
The last important troublesome consideration with the trailing wire system is the flexibility of the cable. It must be wound on a drum of
sufficiently large diameter to preclude work hardening and fatigue breaking of the wires, shields and insulation.
It will be desirable to mount the cable reel to the towing cable drive sheaves so that transient accelerations in the trailing wire can
be minimized. This will also make the cable speed and acceleration
char-acteristics the same as the carriage, resulting in minimum towing cable forces.
D. Control Signals
As discussed in Sections A and B above, control signal channels are required for both directions and both carriages of the 380 foot USNA
.
Towing Tank. The discussion pertaining to telemetry links v.s. trailing wire
cable is applicable to the control signals in every respect discussed in Section C above. The selection of a trailing wire system makes 2 directional
transmission possible without the use of transmitters, receivers, or antennae,
etc. A decision has to be made, however, as to whether the signals are to be
processed in parallel or whether they can be time .shared in series. There are
also two ways to effect parallel operation. The first is to use parallel wires in the trailing wire cable and the second is to use a limited number of wires and frequency share these by the use of frequency shift keying of tone
os-cillators.
Parallel Wires
Referring to the requirement table it can be seen that the number of control functions is relatively large. To make one wire or one wire pair available for each logic function is not practical because of the re-sulting cable size.
Frequency Shift Keying of Tone Oscillators
Parallel operation of up to 20 channels on one wire pair is possible using commercially available components. Receivers and transmitters can be located at either terminal of the system provided only that the same frequency is not duplicated. This system can even be superimposed on the trailing cable power wires since there is no interference from the 60 hz already on the wires.
There are, however, disadvantages. The available units are costly compared to a digital system. Size and weight are considerably greater
than the equipment required for a serial digital data link. There is a speed advantage in the FSK system relative to a digital system in that the parallel channels do not require a data frame to be completed before the control action
is initiated. The relative speed, however, is not greater than 2 to 1, i.e.,
approximately 1/20th of a second. The added speed is not required, and if it is the data rate of a digital system can be upgraded to exceed anything that is possible with the standard available tone oscillator system.
3. Digital Serial Control Data Link
The implementation of a digital data link for control functions, displays and interlocks requires 3 twisted pairs in the trailing
wire cable. The first is for transmitting a synchronizing clock pulse train
to the logic system in the carriages. The second is for data words from the shore to the carriages and the third is for the return signals. The main advantage of this system is that it uses some of the available components
from the speed control system, for example the clock, and uses the same logic
components in a compatible packaging system as the speed control, thus en-hancing the overall operability of the towing tank electronic system. By the
same token it is lighter, smaller and more economical than any other system
considered.
E. Power Distribution System
1. On-Board Power - High Speed Carriage
The battery requirement for the high speed carriage in the absence of a power cable must be compatible with a need for up to 2 kilowatts,
though the time period is short. Aircraft batteries are designed for this
type of service. Using a 20 amp-hour battery at a 200 ampere rate, the
required power is available for 5 minutes. The battery would require charging -preferably at a slow rate between runs if this much power is used. Such a
battery weighs approximately 50 pounds
Another battery weighing 80 pounds and having appropriately bigger capacity can be used. Rechargeable batteries such as NiCad made by Gulton have the highest amp-hour per pound capacity of the aircraft types.
- These batteries require servicing and maintenance in addition to normal
re-charging, if they are to provide an adequate number of charge-discharge cycles. System operability will be much simpler for the towing carriage if batteries
can be avoided.
2. Inductive Trolleys
It is possible to transfer power to a moving vehicle using inductive techniques. This scheme is discussed in Reference 1 in connection with high speed propulsion. The conclusions drawn there are that in order
to transfer significant power, a ferrite device is used to provide close coupling between the stationary line and the moving pickup. These devices
work best at high frequency. Further, the transmission line properties of the stationary system will have a characteristic impedance due to their
geometry. In order to pass current into the pickup it will therefore be
necessary to operate at high voltages.
High voltage at high frequency are undesirable from several
points of view: first, they must be generated in amounts sufficient to
pro-vide 2 KVA on the High Speed carriage at 60 to 80% efficiency, and 20 KVA
minimum on the Low Speed carriage; secondly, the system would be experimental in nature because such systems are not generally in use, and design parameters are not readily available, and thirdly, there would be interference generated which may fall within the passband of the desired analog data which would be
very difficult to overcome because it is generated at such a large power
level.
Power Rails
To transfer 40 kw, and up, to the low speed carriage will require power rails. These systems are usually used for monorail trains, cranes, hoist cars and other towing tanks. Current handling capabilities start at 60 amperes and go higher. The USNA towing tank application is
therefore at the lower end of this capability, since an off-board propulsion system has been selected. The voltage carrying capacity is also generally higher than is required for the towing tank.
There are a number of schemes for covering the rails so as
to make them inaccessible to accidental contact by personnel in the area. An
extruded plastic or a sheet steel housing is used with the rail and the multi-contact trolley is inside the housing. The wires from the pickoff trolley to the carriage can
be insulated.
Cable Containing a 16 Gauge Quad
A 4 wire twisted quad consisting of 16 gauge wire could be used for the high speed carriage. Using a 208 volt 4 wire system, this would require about 6 amps per line. At 6 amps per line the voltage drop in 500 feet of cable will be approximately 15 volts. This can be compensated by stepping up the incoming power to 223 volts line-to-line.
An alternate solution is to use 480 volt 4 wire at 3 amps per line to the carriage and step down the voltage on the carriage. This
would not cause changes in the planned cable design.
A further use could be made of the 16 gauge power wires by applying the Frequency Shift Tone Control Signals to two of the power wires.
F. Electromagnetic Interference
There are a number of areas of great concern when considering the Electromagnetic Interference Environment for the Naval Academy Towing
Tank. These are: the presence of the Naval Radio Station, other major
interference sources within the building, the interference that may be gen-erated by the towing tank propulsion system, and the carriage instrumentation.
1. Instruments and Cables
The instruments and associated cabling must be shielded. The signal cabling must consist of twisted pairs. The return wire in a twisted pair is subject to the same magnetic fields as the signal wire and stray signals induced will tend to cancel. By being very careful in isolating each signal ground from all other grounds and particularly power ground, it will be possible to eliminate ground loops and the signal impressed on a wire pair will not be distorted by the voltage drop due to currents in return wires. Each return wire must be treated like a signal wire to achieve this. All
shields will be grounded using a scheme which will minimize currents in the
shield. The effect of the shield will be to reduce the capacitive coupling
between channels in the cable and from the power lines.
The use of twisted power lines will reduce the magnetic fields set-up within the cable itself.
2. Outside Sources
The Naval Radio Station, and other laboratories within the engineering building, are sources of interference which must be considered. The radio station operates between 21.4 Khz and 27 Mhz with 65 to 70 trans-mitters on the air at all times. Power levels presently range up to 1 MW. The problem is that at the 20 Khz end, the data channels cannot distinguish
interference from signal, because the data channels are required to have good response up to 20 Khz. Indeed the small hydrophones, the basic flow noise instrument, are capable of responding up to several hundred Khz. This means
that it will not be sufficient merely to filter out the interfering frequencies from the data channels. Interference must be eliminated before it enters.
The specific characteristics of the equipment in the
engineering building causing interference will not be known until the design
is completed. Some problems can, however, be anticipated. Digital computers
and their associated teletype machines are a source of conducted as well as radiated interference.
In order
tobe
able to provide effective groundof
theelectrostatic and electromagnetic shields that will be required in the system, a good ground plane for the building is recommended. Shielded enclosures around susceptible components should be included in the system design. Care
must be taken not to conduct the radiated interference into the shielded enclosure through openings for shafts and ducts.
3. Propulsion System Generated Interference
The Power Amplifiers of the propulsion system are a possible source of interference at the frequencies of interest in the data gathering
system. The control circuits within the power amplifiers are also susceptible
to outside interference. It will be necessary to reduce both of these effects. The possibility of filtering the power lines to eliminate some of the effect of the power amplifiers seems very remote. The amount of power involved and size of the required components make this an expensive and impractical solution. Interference reduction will be an inherent part of the power amplifier design to the extent the present state of the art allows. The control system and amplifiers will be in a shielded enclosure, or enclosures, to reduce the
effects of radiated interference. One step towards reduction of the conducted interference is to use separate power transformers for the towing tank pro-pulsion system, isolated from the rest of the power mains in the Engineering Studies Complex.
4; Reinforcing in the Concrete as an RF Shield
In order to make use of the shielding effects of the rein-forcing steel in the concrete, two steps are required. The steel must be placed in the form of s mesh with all intersections welded. This will act as a shield for low frequency. The largest dimension of the space in the mesh will determine what wave lengths are excluded; e.g. if the vertical bars are
3 inches apart but the horizontal ones are 30 inches apart, then the 30 inch dimension will be the controlling dimension.
The second requirement is that the reinforcing mesh be
properly grounded.
With the reinforcing bars welded and grounded the
con-figuration approaches a woven material. The shielding effectiveness of this type of structure cannot be calculated but must be established by test
(See Reference 2). The trend, however, is:
the smaller the aperture, the more effective the shield.
magnetic shielding is less at low frequency and
increases as frequency goes up for a given mesh.
c radiated shielding is higher at low frequency and decreases as frequency goes up for a given mesh.
The cost of welding the intersections and bonding to ground will probably not justify the amount of shielding obtained unless the
apertures become small.
G. Selected System
1. Data Analysis Interconnections
Figure 1 shows a plan view of the Towing Tank facility.
The location of the trailing wire cable trough and the cable drum connected to the main propulsion cable drive shaft can be seen in this illustration.
The control room contains the carriage control panel and
the electronic equipment racks. A connector panel on one of these racks
contains a set of BNC connectors from which the analog data is available. Cables from this patch panel transfer the data to the PDP 15/40 in the
engineering computer center on the second deck of the Engineering Studies
26
Complex. The recorder start and stop signals and the TV signal are also
available on this panel. Sufficient space has been made available in the control room for the installation of a dedicated computer when the towing tank workload and the availability of the central computer justify this
approach.
Analog signal patching can be accomplished in junction boxes on both carriages. BNC connectors are available on panels near the experimental module mounting rails on the two carriages. This also permits
the use of on-board recorders as backup.
Another access to instrumentation signals is provided in the low speed carriage control cab. Provision is made in the cab for installing a mini-computer and tape recorders. The computer will be used for data formatting and automatic control of experimental runs.
2. Cable and Slip Rings
The conclusions of the considerations in the previous sections are summarized in Table 3 on the following page. A cable system was selected for the high speed carriage. The cable consists of:
15 pair #24 AWG twisted and shielded MIL-W-16878,
Type B
3 Coaxial Cable RG-187/U
4 #16 twisted quadruple MIL-W-16878 Type C.
Braided copper shield over the conductors and an abrasion resistant polyurethane jacket over the cable. The cable will be procured in
TABLE 3. ELECTRICAL INTERFACE IMPLEMENTATION
28
power rails.
ITEM REQUIREMENT SOLUTION
1. 8 analog channels 8 wire pairs in the trailing cable
9.
1 TV channel I coax in the trailing cable3. 13 high speed carriage remote Part of digital data link in the
control channels trailing cable - 3 twisted pairs
4. Interlocks denoting carriage condition
Same as 3.
5. Low speed carriage numeric speed readout (4 digits)
Same as 3.
6. Low speed carriage en-board
speed control
Same as 3.
7. Acceleration control 1 wire pair in trailing cable
8. Seventeen low speed carriage control panel status
indi-cators
Same as 3.
9. Seven control system controls activated from low speed carriage
Same as 3.
10. High speed carriage power Wire quad in trailing cable
11. Low speed carriage power Four power rails
12. Intercom Twisted pair and coax in trailing
cable
13. Emergency stop Wire pair in trailing cable
14. Safety ground One of the power wire quad in the
The cable is reeled in and out on a drum on the main
pro-pulsion cable drive shaft. Slip rings and a rotary joint for the coaxial
cable recover the signals from the cable. An assembly of 50 slip rings and a coaxial rotary joint for TAT. signals is housed inside the cable drum. Figure 3 illustrates the cable drum and feed mechanism.
The use of low impedance signal lines and double brush assemblies, using silver graphite brushes, will assure low noise due to
slip rings. The rings are coin silver and are rated to 5 amperes. Copper
rings with heavier brushes can be used for power up to 50 amperes. However,
for this application in order to keep the rings of the assembly compatible, the power will be carried by a pair of signal rings. Eight rings are
therefore reserved for high speed carriage power and the remainder are used for twisted pair shielded cables. The two coaxial cables, not used for TV signals, are connected to two pairs of slip rings.
Table 3 compares the selected system with the requirements established at the beginning of this discussion in Table 1.
3. Digital Control Link
The trailing cable from the high speed carriage to shore includes three twisted pairs
for
the digital control link. The first pair carries the timing and synchronizing pulses derived from the 1 Mhz output of the Frequency Synthesizer which is used primarily in the speed control system.Three digital words of sixteen bits each are serially transmitted to the high
speed carriage on the second pair, and from the high speed carriage on the
CARRIAGE PROPULSION CABLE SLIP RING ASSEMBLY TRAILING WIRE ELECTRICAL CABLE .A1C, FEED MECHANISM CABLE DRUM MAIN DRIVE MOTOR SHAFT FIXED ELECTRICAL CABLE
-DRUM'
MAIN DRIVE "...MOTOR SHAFT
FIGURE 3
CABLE DRUM AND FEED MECHANISM
The first word to the carriage is concerned primarily with instrumentation functions which can be remotely controlled from the shore, using four bits of the word to address which (if any) of the eight analog data channels is to have its gain change capability activated, and two bits to establish whether increase, decrease, or no change. One bit each is used
for turning on the recorder, TV System, lights, and photographic camera. Two
bits are spares. Two of the sixteen bits are used for parity and error
checking. Another bit turns on the warning light prior to and during a run.
The final bit of the word carries the command to retract the arms which
normally engage the secondary return brake, enabling the carriage to be jogged
into the drydock.
The second and third words to the carriage are relayed through the high speed carriage to the low speed carriage, if coupled. If
uncoupled, these words are meaningless. The second word has one spare bit, two bits for parity and error checks, ten bits to control the status lights for the independent functions displayed on the control panel, and three bits coded to light none or one of the seven mutually exclusive carriage operating modes (Jog, Run to Wavemaker, Track to Drydock, etc.). The third word includes the sixteen BCD bits required to display carriage speed on the Low Speed
Carriage control panel.
The first word transmitted from the carriage to the shore includes two bits for parity and error checks, five spares, and six bits denoting status of the interlock functions concerned with the high speed carriage condition (coupled/uncoupled, slippers up, tow cable pretension,
brake arm retracted, and catwalk lowered). These signals are used in the safety interlock logic to restrain operation as necessary. The remaining three bits of the first word to shore carry the commands from the manual functions performed at the low speed carriage control panel during jog.
The second word from the carriage to the shore relays the momentary controls and contains two parity and error check bits, five unused
spare bits, three bits for "Stop", "Initalize", and "Start" commands, three bits for recorder control (off, on, automatic), and three bits coded for the seven mutually exclusive operating mode presets.
The final word to shore is comprised of sixteen bits of BCD data which come from the low speed carriage control panel "run speed" control switches when the system is not in the track mode.
The timing pulses will be at least 500 HZ in frequency so that three words can be transmitted in not over 100 milliseconds (96 milli-seconds for the bits and 4 or less millimilli-seconds for timing pulses), hence the maximum delay between a command and system reception thereof is 100 milliseconds. "Emergency Stop" is not delayed, therefore it is not included in the multiplexed control link.
4. T.V.
The trailing cable from the high speed carriage includes
two coaxial cables type RC-1871J; one carries the closed circuit TV signals,
and the other will be a spare. The signal carrying coax is terminated at both the carriage instrumentation module junction box end and the control room in an isolated coaxial connector, type TNC. This connector differs from
those used for other data transmission for ease of identification and relative
permanence of connection.
Intercom
The trailing cable from the high speed carriage includes a twisted shielded pair and a third coaxial cable type RG-187U for the exclusive use of the voice communication system between the control room operator and the low speed carriage control panel location and/or an operator at one of the instrumentation module junction boxes on the high speed or low speed carriage. The twisted pair and its isolated shield will carry up to two low impedance
(330 ohms or less) microphone signals independently to a voice amplifier in the main control room electronics rack and hence to the earphones of the
operator at the main control panel. The coaxial cable will carry the amplified voice signal from the main control panel operator to connectors on the on-board control panel and the active instrumentation module in parallel. The two
carriage stations can communicate with the control room, but not with each other. Emergency Stop
The trailing cable from the high speed carriage also includes a twisted shielded pair for "Emergency Stop". Making an electrical connection between the wires
of
the emergency stop pair immediately commands a maximum deceleration stop for the system.Power Rail for the Low Speed Carriage
The system consists of 4 rails carrying 3 Phase 60 HZ power
and a neutral. Current carrying capacity for each rail is at least 220 amperes.
Line voltage between rails will be 208 volts and between power rails and the neutral rail, 115 volts.
A current collector articulated in a pantograph configuration capable of 100 amperes is supplied for each of the 4 rails.
The pickup arm speed can be any speed from 1/2 ft/sec to 25 ft/sec (30 to 1500 ft/minute).
Large periods of time will be spent at rest.
A housing protects personnel from coming in contact with the
power rails.
The 100 ampere capacity of the pickups assures an available power of 30 KVA on the carriage initially. The rails are capable of supplying twice that current, thus assuring a future expansion capability of up to 60 KVA.
REFERENCES
White, D. C., Thornton, R.D., et al. Some Problems Related to Electric
2raal1sism,
MIT, Department of Electrical Engineering, November,1966.
Air Force Systems Command Series 1-0, DI1-4,
Lulu"
Handbook, Electro-magnetic Compatibility, Section F, Chapter 5, Design Note 5F7, P. 1,10 January 1969.
Jarvis, R. L., et al, Development Studies for the U. S. Naval Academ nigh Performance Towing Tank; AAI Corporation Engineering
Report No. ER-6157, May 1970.
Schroeder, F. J.; Johnson, B., Design Summary of the USNA 380 Foot High Performance Towing Tank, Report E-71-2, US Naval Academy.
35 2.
