NAVY DEPARTMENT
THE DAVID W. TAYLOR MODEL BASIN

WASHINGTON 7, D.C.

NW HOTS

pocu fAaT 1T |
\ COLLECTION /
Me

THE TMB AUTOMATIC SHIP'S MOTION RECORDER

by
Norman H. Jasper \4
wp oe
) /
7
October 195| Report 777

NS 731-037

INITIAL DISTRIBUTION

Copies
24 Chief, BuShips, Project Records (Code 324), for distribution:
5 Project Records
1, Technical Assistant to Chief of the Bureau (Code 106)
1 Research (Code 300)
1 Applied Science (Code 370)
1 Hull Design (Code 440)
1 Bureau of Medicine Liaison (Code 405)
1 Preliminary Design (Code 420)
2 Scientific (Code 442)
1 Stability (Code 444)
1 Carriers (Code 512)
i! BB, CA, DD (Code 513)
1 Submarines (Code 515)
1 Auxiliaries (Code 517)
1 Navigational Equipment (Code 524D)
1 Electrical (Code 560)
1 Internal Communications and Fire Control (Code 565)
1 Gyro Compass (Code 565h)
1 Electronics Design (Code 810)
1 Radar Systems (Code 820)
2 Director, Naval Research Laboratory, Washington 20, D.C.
1 CDR, New York Naval Shipyard, Materials Laboratory, Brooklyn 99, N.Y.
1 CDR, Puget Sound Naval Shipyard, Code 251, Bremerton, Wash.
1 CDR, Boston Naval Shipyard, Boston 29, Mass.
] Chief of Naval Operations, Operations Evaluation Group, OP374, Navy
Department, Department of Defense Building, Washington 25, D.C.
1 Chairman, Research and Development Board, Department of Defense
Building, Washington 25, D.C.
1 Commandant, U.S. Coast Guard, Headquarters, 1300 E St., N.W. Wash-
aeeenor 25)5 16.
1 Director, Special Devices Center, Office of Naval Research, Sands
Point, Port Washington, L.I., N.Y
1 Director, Office of Technical Services, Dept. of Commerce, Wash., D.C.

6 British Joint Services Mission (Navy Staff) 1910 K St., N.W., Wash.,D.C.

Copies

1 Engineering Research Institute, University of Michigan, Ann Arbor,
‘ Mich., Attn: Prof. J. Ormondroyd

2 Schaevitz Engineering Company, Camden, N.J.

/

TABLE OF CONTENTS

ABSTRACT .

INTRODUCTION .

BACKGROUND AND GENERAL DESIGN CONSIDERATIONS .
THE RECORDER .

THE TRANSDUCERS

PRINCIPLE OF OPERATION .

DISCUSSION AND EVALUATION

CONCLUSIONS

RECOMMENDATIONS

ACKNOWLEDGMENT .

APPENDIX 1 - SPECIFICATIONS FOR AUTOMATIC SHIP'S MOTION RECORDER .
s

APPENDIX 2 - INSTRUCTIONS
REFERENCES .

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THE TMB AUTOMATIC SHIP'S MOTION RECORDER

by

Norman H. Jasper

ABSTRACT

This report describes the development of an automatie ship’s motion recorder
which records the ship’s rolling, pitching, and heaving accelerations as well as the
rolling and pitching angles. The recorder has provision for automatic sampling of
data at preselected intervals of time, and it can operate continuously for weeks on ship-
board without requiring human attention. The apparatus may also be used to record
quantities other than those mentioned, for example, pressures and strains.

The recorder and the transducers are evaluated on the basis of their perform-

ance so far, and further worthwhile developments are suggested in the report.

INTRODUCTION

The function of the TMB automatic ship's motion recorder is to re-
cord automatically the heaving, rolling, and pitching accelerations as well as
the rolling and pitching angles of ships. Its record provides the data needed
for a statistical analysis of ships! motions. Briefly, the recorder registers
the output of five transducers as a function of time, for a predetermined dura-
tion, at preselected intervals of time; that is, it performs a sampling opera-
tion. The unit described in this report is set to record for a duration of
two minutes at hourly intervals.

This device was developed as part of a program, authorized by the
Bureau of Ships,’ to study the strength of ships at sea.* There are many oc-
casions when it would be of considerable value to know the actual motions
which ships may be expected to have at sea, for example in designing masts,
flight decks, hulls, and supports for machinery and instruments as well as in
the design of equipment mounted aboard ships and—to mention quite a different
field—in the study of physiological aspects of ship motions.

1References are listed on page 26.

*A general discussion of a proposed program for the study of the strength and motion of ships at
sea will be given in another TMB report. See also References 2 and 3.

To date there is but little organized information available on the
actual rolling and pitching angles of ships and even less is known about the
bodily acceleration of ships. It is the function of this recorder to provide
such information without requiring personnel for the operation of the equip-
ment. The present model of the TMB automatic ship's motion recorder was in-
stalled on a Coast Guard weathership during a 2-month tour of duty in the
North Atlantic in the spring of 1951. The recorder and pickups operated con-
tinuously during this time and gave satisfactory service.

This report will give some background leading to the development of
the apparatus; the recorder and the pickup devices will be discussed and rec-
ommendation for further development will be made.

BACKGROUND AND GENERAL DESIGN CONSIDERATIONS

The lack of information on the motions of ships at sea is due pri-
marily to the physical and financial difficulties that have been present in
attempts to obtain such full-scale data. The cost involved in providing in-
strumentation and personnel, with use of the ordinary methods of recording
data, prohibits such trips except on rare occasions; therefore such methods
cannot provide a sufficiently broad basis from which mean and probable peak
values can be determined for given ships operating in the various seas.

It was considered, therefore, that much profit might be derived from
the development of some automatic device which would record the desired quan-
tities over long periods of time and which could be installed aboard a ship
and left there unattended, except for the purpose of removing the data at in-
tervals of several weeks or months. Obviously the .apparatus would need to be
rugged and, if it is to be utilized on a large scale, inexpensive. .

Quantities that enter directly into structural design are the accel-
erations associated with the rigid-body motions of the ship as well as the
angular position of the ship in the gravity field. These accelerations vary
relatively slowly with time and their magnitude is generally less than the ac-
celeration of gravity. Throughout a ship there are usually high-frequency
local vibrations present, which are undesirable for our purpose since they
give rise to accelerations of the same or greater magnitude than those due to
the rigid-body motions of the ship. It is necessary that measurements be kept
free of these higher-frequency components so as not to obscure the desired
information.

The measurement of angular acceleration involves considerable diffi-
culty. There dces not appear to be a suitable instrument available which will
measure the required rather low values of.angular shipboard acceleration with
sufficient accuracy. A measurement of angular acceleration may be obtained by

utilizing a set of linear accelerometers. Signals proportional to the rolling
and pitching angles may be obtained from gyroscopic stable elements. It is
necessary that the stable element have a long natural period as compared with
the periods of the motions to be measured.

It was decided that a device should be developed which would measure
and record the heaving, rolling, and pitching accelerations of a ship and, in
addition, have two spare channels available which could be utilized for record-
ing the rolling and pitching angles or, alternatively, some other quantity
such as strain. To reduce the cost, standard components were used as much as
possible, and refinements in the prototype model which were not needed for an
effective evaluation of the suitability of the basic apparatus were omitted.

Since analysis of records is a laborious and time-consuming opera-
tion, the apparatus was designed to be used as a sampling device, that is, to
record the data only for a relatively short duration at preselected intervals
of time. Thought was also given to providing means which would cause a record
to be made only when the value of the measured quantity exceeded a preselected
magnitude. However, this was considered to be one of the unessential
refinements.

Inasmuch as the equipment was intended to operate aboard ship over
long periods of time, including storm periods, it was felt desirable to re-
quire that the apparatus operate from power normally available on most ships
at the voltage regulation of such power sources. Furthermore, the instruments
and the recorder had to operate satisfactorily under the environmental con-
ditions aboard ship at all time.

Appendix 1 will give the specifications that were established in
view of the considerations just discussed. The recorder and the accelerom-
eters which are at present used with it, have been developed at the Schaevitz

Engineering Company, Camden, New Jersey, in accordance with specifications
drawn up by the David Taylor Model Basin.

THE RECORDER

The recorder is essentially a direct-recording oscillograph which
has provision for automatic sampling and which is designed to operate continu-
ously for weeks on shipboard without human attention. The unit is shown in
Figures 1 through 6. Its over-all size is 19 3/4 inches wide, 15 3/8 inches
high, and 15 1/4 inches deep. All necessary amplifiers, servo-motors, etc.,
are contained in the case. The only external connections to be made are those
to the transducers (pickups) and to a 60-cycle 110-volt a-c power source. The
recorder has a frequency response which is flat within 5 percent from d-c to
1 cycle per second. Higher frequency signals are attenuated.

TMB 46079}

Figure lb - Back

Figure 1 - TMB Automatic Ship's Motion Recorder

Soeer ees

a1buy uriid

pec saee sd

fon Be ae 8

TMB 46078 8

with Front of Case Opened

- Recorder

Figure 2

2 minute Gam—

Chart Magazine

Takeup Spool

TMB 46080

Recorder with Chart Magazine Removed

Figure 3

Zero Adjustment

TMB 46082

Figure 4 - Back of Control Panel

TMB 4608!

Figure 5 - Amplifiers Installed in Recorder

a io aes
We NN
ay

TMB 46083

Figure 6 - Recorder and Accelerometers

Figures 2 and 3 show a front view of the recorder with its airtight
cover opened. There are 5 channels and 2 sensitivities (X1 and X3) available
per channel. The lower sensitivity will usually be used. Each recording pen
has a chart strip 2 inches wide provided for it, and positive stops are pres-
ent which limit the travel of the pens to this value; the pen drive motors
cannot be overloaded. The chart speed-control lever can be seen at the far
left of the photographs. It permits a selection of speeds of 1/2 oe 1 stain
per minute; these chart speeds are sufficient to give ample resolution of the
oscillograms for the purpose intended. The recording chart (Figure /) has
a plastic-coated surface which is sensitive to pressure applied by the record-
ing pens; the surface does not smudge with ordinary handling.

Normally the unit will be used as a sampling device, and a record
of 2 minutes duration will be made at hourly intervals. The procedure is as
follows: The power is turned on and about one hour is allowed for the unit to
warm up. Then the chart drive switches are thrown to the "ON" and "TIMED"
positions. The recorder will now take a record at hourly intervals. If it is
desired to record continuously, it is merely necessary to throw the chart
drive switch to the "CONTINUOUS" position. If, while the recorder is set for
the automatic cycling operation, it is desired to record continuously for a

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Figure 7 - Sample of Recording Chart

®
predetermined period of from 5 minutes to 113 minutes, it is merely necessary

to turn the "MANUAL SET TIMER" to the desired time interval; the recorder will
immediately start to record and at the end of this interval will automatically
return to the automatic cyclic operation.

The supply and takeup spools for the chart paper are mounted in a
single removable magazine as shown at the bottom of Figure 3. One spool is
sufficient for 50 days automatic operation at the lower chart speed. Differ-
ent chart speeds could readily be obtained by a change of gear ratios. The
entire unit may be mounted in a standard rack, or it may be shock-mounted.

The over-all sensitivities of the several channels are given in
MALE I

TABLE 1

Sensitivity of the Several Channels of
TMB Automatic Ship's Motion Recorder

Range on Range on Sensitivity|Over-all Sensi-
Quantity Attenuator | Attenuator tivity of Trans-
Measured _—{X1 X3 cea ducer and Re-

(full scale) (full scale)|] deflection corder
(Attenuator X1)

Channel

Heave ate ate 1 inch/g*
Acceleration

Roll Accel- 2 inches/g* or

eration 1 inch/rad/sec**

Pitch Ac- 2144 raq/ 4 inches/g* or
celeration 2 in/rad/sec***

Roll Angle

Pitch Angle

*g is the acceleration of gravity.

**Sensitivity of 2 linear pickups 16.1 feet apart, wired in series opposition.

THE TRANSDUCERS

The recorder may be used to record the voltage output of a variety
of transducers provided the frequency of this voltage is the same as that re-
quired to drive the two-phase pen motors. For our purpose, however, we will
discuss the operation of the particular transducers that have been used to de-
termine the heaving, rolling, and pitching accelerations as well as the roll-
ing and pitching angles of the ship.

10
@

The accelerations are measured by pickup devices which are essen-
tially identical. These accelerometers utilize a "linear variable differen-
tial transformer" (LVDT) as the sensing element.

This transformer consists of a secondary and two primary windings
wound on the same axis, with the secondary located between the primaries. The
primaries are connected in series so that the voltages they induce oppose each
other. When an iron core is placed on the axis of the LVDT and symmetrically
located with respect to the primaries, the output of the secondary is a mini-
mum (practically zero). This is the null position. When the core is moved in
one direction from the null position, the voltage induced in the secondary by
one primary will increase while that induced by the other primary will de-
crease. The net result will be an increase in output voltage directly propor-
tional to the core displacement, and the phase of this voltage will depend on
the direction of the displacement from the null position. To operate as an
accelerometer the displacement of the core is made proportional to accelera-
tion. A signal proportional to angular acceleration is provided by connecting
the output of two linear accelerometers in series opposition. On the Coast
Guard weathership, two linear pickups were spaced 16.1 feet apart to give the
desired angular acceleration signal.

A signal proportional to the rolling and pitching angles may be ob-
tained either directly from the output of a stable element, or, alternatively
from a potentiometer driven by a servo system which in turn is actuated by a
stable element. For greater accuracy more refined methods can be devised.

It should be noted that the transducers as well as the recorder and
amplifiers are designed for 60-cycle 110-v a-c operation. They could just as
well have been designed for an a-c supply of higher frequency.

The accelerometers were obtained from the Schaevitz Engineering Co.;
their specifications are given in Table 2.

PRINCIPLE OF OPERATION

In the schematic diagram of Figure 8, it is seen that the outputs of
the secondaries of two differential transformers (LVDT) are connected in
series opposition. One LVDT is located in the recorder, see Figure 4. Each
produces a 60-cycle a-c output.

The sum of the outputs of the two LVDT's is amplified, its phase is
shifted electrically 90 degrees, and then impressed on one phase of a two-
phase motor; the other phase of the motor is directly excited from the a-c
power supply. This two-phase motor in turn drives both the pen and the core
of the balance LVDT until the output of the balance transformer's secondary is
equal to that of the accelerometer's secondary, resulting in zero voltage

WW

TABLE 2

Specifications for Schaevitz Accelerometers
Sensitivity - Open

Cireuit mv. output

of Turns| per volt input at
per Coil] 60-cycle a-c

for 0.001 inch core
displacement

Designa-
tion by

Accelerometer Transformer Accelerometer Transformer
Secondary Primary Secondary Primary
ae,-a€,

To Amplifier
6v a-c

Fave =

To Amplifier

Adjust Range 6v a-c

Amplifier
Ground
= To Amplifier - To Amplifier
Amplifier Input Input
Ground
X=S x-3
oO ie)
Range Selector Range Selector
itch witch
Switc 30n Swi
| Adjust Range
pal Be
Secondary Primary Secondary Primary
Balance Transformer Balance Transformer
Channel | Channels 2,3,4,5
Linear Accelerometer Angular Accelerometers

Figure & - Schematic Diagrams of Null Balance Circuits

12

input to the amplifier. In short, the follow-up system is arranged so as to
balance the sum of the transformer voltages to zero.

If greater pen deflections are desired for a given transducer signal,
it is only necessary to tap off a smaller portion of the output of the balance
transformer's secondary since this will require the motor to drive the core of
the balance LVDT through a greater distance in order to null the system; and
of course, the pen motion is directly proportional to the core motion.

The primaries of both transformers are connected in series, likewise
the secondaries. This insures freedom from disturbances due to changes in
line voltage; since line voltage changes will affect each transformer equally,
the net change will be zero.

Figure 4 shows the location of the balance LVDT's and the adjusting
screws for manually moving their cores in order to center the corresponding
pen on the chart. The screws marked "ADJ RANGE" permit adjusting the sensi-
tivity of the several channels. The amplifiers, one for each channel, may be
seen in Figure 5.

Detailed circuit diagrams and operation instructions are given in
Appendix 2.

DISCUSSION AND EVALUATION

In discussing the instrumentation it will be appropriate to discuss
the recorder and the transducers separately since they are, in fact, complete
in themselves.

The recorder and transducers were installed on the Coast Guard
weathership USCGC CASCO, a vessel 310 feet in length, while on a duty tour in
the North Atlantic from 11 March to 12 April 1951, a total of 32 days. The
equipment was operating during this entire trip except for a day's interrup-
tion due to failure of a relay, which has since been replaced by a more rugged
unit. The performance of all units was entirely satisfactory during this
trip—especially when one considers that it was the first time the equipment
had been given a service test. The maximum measured values during this voyage
were: Roll of 37.5 degrees double amplitude, pitch 18 degrees double ampli-
tude, heaving acceleration 0.8 x gravity, pitching acceleration 0.5 radians/ —
sec’, and rolling acceleration 0.20 radians/sec*. All of these are double
amplitude or peak-to-peak values. The voyage may be considered to havé pro-
vided rolling, heaving, and pitching conditions of the maximum order of magni-
tude to be expected.

13

The recorder in its present form did the job well for which it was
designed. It has shown itself to be rugged and reliable with the exception of
two minor items, namely the relay failure mentioned above and a cam follower
which should be made of somewhat heavier steel strip. It would be a great con-
venience to incorporate into the recorder mechanism a device which would auto-
matically stamp the date and time on the record whenever a record is made.
Other desirable refinements would be a provision for a greater chart capacity,
say 200 feet, and two or three additional recording channels in order to per-
mit recording of strain, ship's speed, and heading simultaneously with the
other quantities.

The mechanical design of the recorder is very compact and utilizes
subassembly construction, making for easy servicing. Many parts are standard
items, readily available. The cost of the recorder including the three accel-
erometer units was comparatively reasonable, but if additional channels were
added the cost may increase somewhat disproportionally because a standard
chassis might not be available.

Analysis of the records obtained from the CASCO sea trials has been
made in terms of the number of cyclic variations of the magnitudes (roll,
pitch, etc.) that fell within given limits. Such an analysis can be presented
rather conveniently in the form of frequency distribution curves. This analy-
sis, although readily made by inexperienced personnel, is tedious; it could
be performed automatically by means of a counter system similar to the type
that has been under development for the strain cycle gage, see Reference 3.
Both the chart recording and the statistical analysis provided by the cycle-
counter data could be made available at the same time. The development of
this combination of instruments is highly desirable for the study of the
strength of ships at sea that is presently underway at the Taylor Model Basin.

The following comments concerning the transducers are in order.

The individual accelerometers measure accelerations perpendicular to their
bases, and if the ship rolls, the heaving acceleration measured is the com-
ponent in the centerline plane of the ship. The heave accelerometer will also
be affected by the change in the component of gravity along its sensitive axis.
The error due to the latter cause is generally not serious except for the
larger angles of roll; for the largest measured rolling angle this effect
would be about 20 percent of the total signal. However, the heave at this
time was small. The proper correction can easily be made. Furthermore, these
effects are minimized by the fact that, when the heaving is large, the roll is
generally small, and vice versa. In measuring the angular accelerations, the
effects due to the change in the gravity field or due to linear accelerations
are canceled out.

14

A considerable improvement in the compactness of the installation
would be obtained if single angular accelerometers were available; development
along this line appears worthwhile. However, the combination of two linear
accelerometers, as now used, does give satisfactory service although lacking
in compactness. If it is necessary to measure heaving acceleration in the
vertical plane, the accelerometer must be mounted on a stable platform; the
required corrections can, however, be made from a knowledge of the angle of
roll. It is felt on the basis of data obtained so far that the errors actu-
ally introduced are small, of the order of 10 percent, and that refinements
to correct for the effect of roll on heaving acceleration are not worthwhile.

With regard to the measurement of rolling and pitching angles, it
would be desirable to have a small stable element available especially for
this purpose with an accuracy of about 1/4 degree in pitch and 1 degree in
roll. It should also be mentioned here that a diaphragm pressure gage has
been developed at the Taylor Model Basin which will work with this recorder.

| The accelerometer and recorder combination is linear within 5 per-
cent from d-c to 1 cps. Lack of calibrating equipment for these low frequen-
cies has limited the extent of calibrations.

One item which may require some additional consideration is the
power from which the equipment operates. At present, 110-volt 60-cycle alter-
nating current is used. If, in the future, ship's power of 400-cycle a-c be-
comes standard, it may be advisable to build the motion recorder and its trans-
ducers to operate on the higher-frequency power, which can be done without
much difficulty.

To recapitulate the main points covered here: The recorder and
transducers, in their present form, are dependable and sufficiently accurate
for the intended service. Proposed additional developments are:

a. A time and date stamp.
b. An angular accelerometer (single unit).
ce. A small stable element.

d. A counter to count automatically the number of cyclic variations
that have occurred.

CONCLUSIONS

1. The recorder performs well in the frequency range associated with
the rigid-body motions of ships; it provides sufficient attenuation for high-
frequency signals.

15

2. Both the recorder and the accelerometers may be expected to furnish
trouble-free performance over a period of weeks while installed aboard ship.
It is not expected that any appreciable servicing will be required between
trips.

3. The equipment is relatively insensitive to variation in the supply
voltage.

4. The records provide a clear, immediately visible trace and will not
be smudged by ordinary handling.

5. The over-all accuracy of the system is sufficient for the intended
applications. It is believed to be accurate within 6 percent over the frequen-
cy range from d-c to 1 cycle per second. The recorder itself is accurate
within 5 percent over the same frequency range.

6. The combination of two linear accelerometers to furnish an angular
acceleration signal is somewhat inconvenient to install.

{. The recorder is a versatile unit which may be used as an ordinary
recording oscillograph or as a sampling device. It will provide the desired
information at a very low cost both in securing and analyzing the data. The
records obtained are readily analyzed in terms of the number of times that
given magnitudes have occurred. The phase relationship between the several
quantities can also be determined with an accuracy depending on the chart
speed used.

8. The time required to make certain types of analyses can be reduced
to a minimum by adding a counter device to the recorder which will indicate
the number of times that given variations have occurred.

9. The recorder in its present form has been used to record linear and
angular accelerations as well as angular displacements. In addition, it may
be used to record any quantity that is impressed on it provided a properly
matched input signal is furnished.

RECOMMENDATIONS

1. An automatic date-stamping device should be incorporated in the
recorder.

Bo tNa angular accelerometer should be developed.
3. Small stable elements should be made available for these recorders.

4, Consideration should be given to the addition of channels to the
present 5-channel recorder.

16

5. It is suggested that a number of recorders be built and installed
on many ships in order to provide statistical information on the motions, and
possibly on the strains and pressures, encountered under various operating
conditions. This type of information would be valuable in diverse

applications.

6. It is recommended that a project be set up to develop and build a
statistical counter device, similar to that described in Reference 3, which
would tabulate the variations of rolling and pitching angle, etc., according
to the number of cycles of given magnitudes that have occurred. This device
would be utilized as an attachment to the TMB automatic ship's motion recorder.

ACKNOWLEDGMENT

Most of the success of the development work is due to the persistent
efforts of the Schaevitz Engineering Co. Much of the laboratory and field
work carried out in connection with the evaluation of this equipment was done
by Mr Q.R. Robinson of the TMB Vibrations Division. The project was accom-
plished under the direction of the author.

vif

APPENDIX 1
SPECIFICATIONS FOR AUTOMATIC SHIP'S MOTION RECORDER
1. GENERAL DESCRIPTION OF THE INSTRUMENT

The ship's motion recorder is to record simultaneously, on one chart,
the output of three accelerometers as well as the voltage output of 2 other
transducers whose output may be proportional to angle of roll, pitch, pressure,
strain, etc. All channels shall essentially be alike, but provision shall be
made to obtain different over-all sensitivities.

The operation of the equipment shall be automatic, not requiring
servicing for a period of several weeks. The recorder shall be operated auto-
matically for 2 minutes every hour or other selected time duration at desired
intervals. Transducers are to be energized continuously. A dial-type indi-
cator, graduated from 0 to 2 hours, is to be incorporated in the recorder so
that, at will, continuous recording within this range can be accomplished by
setting a knob on the timer. Another switch, wired in parallel, is to provide
manual "on-off" control of the chart drive. The recorder should incorporate
suitable attenuators on all channels.

2. ACCELEROMETERS

a. Amplitude Range

1 Linear Accelerometer ate ee:

1 Angular Accelerometer +1 radian/sec®

1 Angular Accelerometer +1/2 radian/sec®
b. Frequency Range 0) GO. 5 Cos
ec. Damping About 0.7 of critical damping
d. Linearity +30 percent of actual value at

minimum discernible deflection*

+5 percent of actual value at
1/10 full scale

+1 percent of actual value at
full scale
e. Temperature range over which equipment will be used is 30° to 110° F.

f. The temperature stability of the accelerometers is to be such that,
if a stream of water at a temperature from 32° to 100° F. is passed over the
gage for a period of 10 minutes, there shall be no change in output of the
gage in excess of 2 percent of full-scale output.

*Minimum single amplitude of deflection discernible on the recording chart is 0.005 inch.

18

3. ROLL AND PITCH ANGLE TRANSDUCERS
a. Amplitude Range
Roll +45 degrees
Pitch + 15 degrees
b. Frequency Range 0 to 3 cps

e. Linearity

I+

Roll 1 degree

I+

Pitch 1/4 degree

4. AMPLIFIER AND RECORDER
a. There will be a total of 5 channels.

b. The frequency response of the accelerometer channels should be such
as to give at least 95-percent attenuation at 5 cps and less than 10-percent
attenuation at 1 cps. The frequency response of strain-gage channels shall
be such as to give less than 5-percent attenuation at 5 cps.

c. Paper speed of recorder is to be 1/2 inch and 1 inch per minute. A
record is to be obtained by scribing on pressure-sensitized paper or the equiv-
alent thereof. Provision is to be made for a chart rewind mechanism.

d. Power supply to the recorder will be 110-v a-c 60-cycle at normal
regulation (+10 percent).

e. Accelerometer channels - Sensitivity
The amplifiers are to have the same sensitivity as for all other
channels, but attenuators shall be provided to give over-all sensitivities of:

1 inch and 3 inches per g for linear accelerometer
1 inch and 3 inches per radian/sec* for angular accelerometers

The tolerances for the over-all sensitivities shall be the same as specified
for the linearity of the accelerometers (Item 2d).

5. ADDITIONAL REQUIREMENTS

a. The equipment should be rugged and not require attention for sev-
eral weeks.

b. The equipment is to withstand salty, humid atmospheres.

V9

e. An "on-off" switch is to be provided to energize or de-energize the
complete unit. A locking device should be provided to prevent tampering with
this switch.

d. The chart drive should have the following controls (listed here in
the order in which they take precedence):

i. Manual "on-off" switen

ii. Manually set timer for continuous operation up to
an interval of 2 hours. (This would bypass Switch i.)

iii. Automatic control which will actuate the chart drive
for a predetermined period of time every hour, or
other preselected interval, unless bypassed by the
preceding switches.

6. The contractor is to furnish plans and an instruction book with the
equipment.

20

APPENDIX 2
INSTRUCTIONS
A. RECORDER SYSTEM
1. CAUTION

AC-DC amplifiers are used in this system. Therefore, when the ampli-
fier is mounted, one side of the power line is automatically connected to the
case. It is necessary to be absolutely sure that the case is at ground poten-
tial before making the external ground comnection.

2. Power Supply

Power input connection is at rear of case; use 110-volt 60-cycle

alternating current.
3. Circuit Diagrams
See Figures 8 through 10.
4. Operation

Install the recorder and connect it properly to the power source and
to the transducers (Note the CAUTION, paragraph 1 preceding). Turn the instru-
ment power on, switch all amplifiers on, and permit the units to warm up for
about 15 minutes. The chart drive motor should be in the off position.

To adjust the zero position of the pens proceed as follows. Operate
the amplifier "CAL-OFF" switch to the "CAL" position; this shorts out the sec-
ondary of the transducer LVDT and changes the circuit from a null-balance to
a null-seeking system. Adjust the zeros of the several pens by means of the
zero adjustment screws, see Figure 4. Throw the amplifier switch to "off."
Now adjust the sensitivities to the required values by means of the "Range
Adjustment" screw. The amplifier gain control may be utilized to reduce hunt-
ing; the gain setting does not affect the over-all sensitivity of the recorder.

To record automatically (cycling operation), the "CONTIN-TIMED"
switch must be in the "TIMED" position and the "CHART DRIVE, ON-OFF, switch in
the "ON" position. If it is desired to record for a definite interval of time
between 5 and 113 minutes, switches are left in the same positions as before,
and the "MANUAL SET TIMER" is rotated clockwise to the desired number of min-
utes; at the end of this recording interval the recorder will automatically go
back to the cycling operation. If continuous recording is required, the
"CONTIN-TIMED" switch is thrown to the "CONTIN" portion.

21

Input Receptacle

| Ground
HOY,AC. Inout

Amplifier
Input 14)

on

750 1500
An an

Aiea

Ghonnel 2

Same as Channel 2

Ghannel 4

Same as Channel 3

Channel 5

Balance

Motor
Balance Transformer
Yellow

Same as
Channel |

} Primary
Yellow

Jock } Secondary
Red

Same as Channel |

1200n

Same os
Channel |

Same as Channel |

2200 n

Control Panel

Same as Channel |

Same aos
Channel

2

Ungrounded Side
. of Phase 2

Same as Channel |

Same as
Channel 3

Figure 9 - Schematic Diagram of Amplifier and Accelerometer Circuits

To Control Panel

Linear Accelerometer
Type DA-2

Primary Secondary

Linear Accelerometer
Type DA-|

Linear Accelerometer
Type DA-2

Primary Secondary Primary Secondary

To Recorder
Channel |

<5= Shield
e = Pin
@ = Pin Receptacie

All Connectors Oriented
Same Way

—— 200 feet ———

To Recorder
Channel 2,3,4, or 5

22

5. Chart Speeds

Chart speed is changed from 1 inch per minute to 1/2 inch per minute
by means of a locking lever arm located at the lower left front end of the
recorder frame. The "down" position corresponds to a 1 inch per minute speed
and the "up" position corresponds to a 1/2 inch per minute speed.

6. Sensitivity Adjustment

The maximum travel of the recorder transformer cores is +£0.010 inch.

This corresponds to full-scale deflection of the pen. For full-scale deflec-
tion, it is necessary therefore to make the output of the recorder transformer
equal to that of the transducer transformer at the desired full-scale trans-
ducer output. This can be accomplished by limiting the output of either the
transducer transformer or the balance transformer by placing a shunt resist-
ance across the secondaries or by tapping off a portion of the voltage with a
resistance divider network.

To InlsGg Ot Comacrols

The various controls are listed below for convenience.

Name Labeled Located
Instrument power "Inst. Power On-Off" Control panel, front
Chart drive "Chart Drive On-Off" Control panel, front
Timing selector "Chart Drive Contin-Timed"” Control panel, front
2-hr timer "Manual Set Timer" Control panel, front
Start 2-hr cycle "Automatic 2 Hr. Cycle-Push" Control panel, front
Range selectors "Sensitivity X3-x1" Control panel, front
1-hr timer "One Hr. Timer" Control panel, rear
Channel 1 range adjustment "Chan 1 Adj. Range” Rear of case
Channel 2, 3, 4, 5 range "Chan 2, 3, 4, 5 Adj. Panel (top rear of re-

adjustment Range" corder frame)
Zero adjustment None Control panel, rear
Amplifier power "Power On-Off" Amplifier panel
Amplifier gain "Gain" Amplifier panel
Calibration "Cal-off" Amplifier panel

B. SCHAEVITZ BALANCE AMPLIFIER TYPE 60 AD
1. Description

The balance amplifier is a specialized amplifier designed for use
with linear variable differential transformers and two-winding, two-phase

Incoming Line Connector

—~=
Main Line to Control Panel

ReiumoiEing 3 Ampere Fuses

—To Amplifiers Terminal 2
Ch.| Gh2 Ch3 Chart Ch.4 Ch5
Drive

<=

To Gontrol Panel
—.

— To Amplifiers Terminal |

Ground Side

Figure 10 - Schematic Diagram of 110-Volt a-c Power Distribution

induction motors. The voltage amplifier portion consists of 4 resistance-
coupled stages, using twin triode 12AX/'s. Cathode degeneration is used to
achieve stability. The power amplifier, a pentode 6AQ5, is resistively
coupled to the voltage amplifier section. No load is provided within the
amplifier for the power tube. The plate circuit is completed through the load,
which consists of one phase of a 2-phase induction motor, shunted by a 1-ypf
capacitor.

Primary power for LVDT's is supplied by the amplifier. The phase
shift through the amplifier is adjusted so that the output of an LVDT is ampli-
fied and applied across the load, 90 degrees in phase from the power-line
phase. Since the second phase of the motor is connected across the power line,
conditions for maximum torque are thereby established. Sensitivity is rated
in terms of the minimum change in input to amplifier which will cause reversal
in direction of motor with full torque. In terms of LVDT output this is equiv-
alent to the minimum change in core position about null which will cause the
Same change in motor operation.

The rectifier power supply is transformerless. It is a grounded
negative-voltage doubler using selenium rectifiers. A low hum level is ob-
tained by attention to details such as grounding, isolation filters, and ar-
rangement of components. With this type of supply, one side of the power line
is connected to the amplifier ground. This is Terminal 1 on the front panel.
It is necessary that this polarity be observed in connecting a power line to
the amplifier.

24

2. Installation and Operation

Three operating controls are provided. The power switch disconnects
the amplifier proper from Terminals 1 and 2. The calibrate switch is used
when two LVDT's are connected in a null-balance system. It shorts out the sec-
ondary of the actuating LVDT and changes the circuit from a null-balance sys-
tem to a null-seeking system. The gain control, available through an access
hole in the front panel, is used to limit the sensitivity to prevent hunting.

No adjustments are required to place the Type 60AD-1 in operation
other than to make connections as shown in Figure 11. However, in the 60AD-2
the internal hum balance control must be adjusted. This is done as follows:
With the normal output load connected across Terminals 3 and 4, connect a
250-v a-c meter across these terminals. Connect a jumper from Terminal 13 to
14. Adjust the control until a minimum voltage is observed on the meter.

3. Maintenance

Since subassembly construction is used, replacement of parts in
maintenance is simplified. The amplifier chassis or the condenser support
bracket may be removed from the amplifier panel by unsoldering a few easily
located connections. The component board in the amplifier chassis can be
freed from the chassis by loosening four screws. Slack in the leads will per-
mit partial withdrawal of this board to allow access to the components.

The first voltage amplifier stage is somewhat sensitive -to heater
induced hum. It would be difficult to select a replacement 12AX/ for this lo-
cation unless an oscilloscope were available. A supply of replacement 12AX/'s
is maintained by the manufacturer. In ordering a 12AX/ it is necessary to
state the type of amplifier and whether used for Stages 1 and 2 or 3 and 4.

An oscilloscope is used to select the first stage tube by ccnnecting
the scope across Terminals 3 and 4 and connecting a jumper from Terminal 13
to 14. The wave shape observed must be free from sharp points (caused by over-
loading due to hum input). The a-c voltage measured at Terminals 13 and 14
should be less than 50 volts. The hum control in Type 60AD-2 must be rotated
to minimize the output.

4. Specifications

Line voltage - 117-v 60 cycles

Power consumption - 40 va (not including line powered phase
of motor)

Sensitivity - 60AD-1 - Complete reversal for 0.00015-inch
core motion of Type 100S Schaevitz
LVDT

60AD-2 - Complete reversal for less than 0.0001-
inch core motion of Type 100S Schaevitz
LVDT

Sze
Figure lla - Schaevitz Balance Amplifier, Type 60 AD-1, Type 60 AD-2

Secondary Primary PH-2

LVDT-1 1.Owvf ©) Motor
: PH-I

8 G 6 5 4 3 2 1 Grounded Side

14 13 12 ul 10 9
(2) fe}
LvDT-2
Secondary Primary

Figure 11b - Null Balance System

PH-2
LOwf @ Motor
500) PH-I
To Line
5 . s S 4 3 2 1 Grounded Side j
14 13 12 tl 10 9
zy =
LVDT
99
Primary

Secondary
Figure llc - Self-Positioning System

Figure 11 - Schaevitz Balance Amplifier and Interconnection Diagrams

Ve

2

26

Power output - Full power 2-phase induction motors to 25 watts
Tube complement - 2 - 12AX/

1 - 6AQ5
Size - 6 5/8 inches by 5 3/16 inches by 4 inches

Mounting centers - 5 inches by 3 5/8 inches
Weight - 4 1/2 pounds

REFERENCES
BuShips ltr S29-8(442-440-330) to TMB dated 21 June 1948.

N.H. Jasper, "A Statistical Approach to the Longitudinal Strength

Design of Ships,” Jour. of the Am. Soc. of Naval Engrs., August 1950.

Do

N.H. Jasper, "A’ Statistical Approach to the Measurement and Analysis

of Experimental Data on Structures," Jour. of the Am. Soc. of Naval ners.,
August 1951.

SSIs