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RESEARCH AND DEVELOPMENT REPORT 
REPORT 784 
6 MAY 1957 


A TEMPERATURE-CONTROLLED TANK FOR CALIBRATING 
REVERSING THERMOMETERS 


J. S. BLACK 


U.S. NAVY ELECTRONICS LABORATORY, SAN DIEGO, CALIFORNIA 
A BUREAU OF SHIPS LABORATORY 


v8Z Hoday /143N 


ON A 


0 0301 0042375 2 


THE PROBLEM 
Develop a controlled-temperature tank for calibrating deep-sea reversing thermometers 
and other precise temperaiure-measuring instruments. 


RESULTS 


A 70-gallon controlled-temperature tank has been constructed and tested. The tempera- 
ture can be reproduced and held to +0.002°C over the range —3°C to 40°C. The tank’s 
large size and remote operation permit calibration of 24 reversing thermometers at 
one time. It eliminates tedious calibration data reduction, since both main and auxiliary 
thermometer stems are read at temperature of reversal. 


RECOMMENDATIONS 
1. Continue development to include installation of electronic time-proportioning switches 


in metering of heat transfer. 


2. Study the possibility of an instrument to record temperatures at two points in the 
tank, throughout any operation. 


ADMINISTRATIVE INFORMATION 

The work was done under IO 15401, NE 120221-13 (NEL L4-1, part 1). This report 
covers work from January 1952 to November 1956 and was approved for publication 
6 May 1957. 

The author wishes to acknowledge the valuable help of J. C. Roque and B. E. Holtsmark 


in functional design of the equipment. Thanks are also extended to A. A. Arnold, Ronald 
Jones, S.L. Polansky, and S. Houseknecht for assistance in the technical design and 


construction. 


CONTENTS 


page 
7) INTRODUCTION 
3 DESCRIPTION OF EQUIPMENT 
10 TEMPERATURE CONTROL UNIT 
11 CALIBRATION OF REVERSING THERMOMETERS 
12 CONCLUSIONS 
13 RECOMMENDATIONS 
ILLUSTRATIONS 
page figure 
3 1 Controlled-temperature calibration facility 
4 2 Circulating system 
5 3 Thermal system 
6-7 4 Calibration tank, shown (A) before reversal of rack, (B) during reversal of rack, and 
(C) with rack removed 
8 5 Tank lid 
9 6 Tank window, reading telescope, and control panel 
11 7 Thermostat and resistance bridge 
INTRODUCTION Ten thermometers can be calibrated at a time against 


The NEL Controlled-Temperature Calibration Tank 
was designed to fill the Laboratory's need for a 
reliable and accurate temperature calibration facility 
for use primarily with deep-sea reversing thermom- 
eters. These thermometers are customarily read to 
0.01°C and, consequently, must be calibrated to at 
least that order of accuracy. A secondary use of the 
tank is the calibration of other temperature-measur- 
ing instruments such as thermistor beads and thermo- 
couples, which may require calibration accuracies 
approaching 0.001°C. 

Accurate calibration tanks have been produced 
in the past. The Dahl-Mosby tank’ which has been 
in operation at the Chr. Michelsen Institutt, Bergen, 
Norway, since 1945, consists essentially of an insu- 
lated cylinder which can be reversed end for end. 


10. Dahl and H. Mosby Calibration Tank for Reversing 
Thermometers (Christian Michelsen Institutt for Videnskap og 
Andsfrihet, Beretninger XI, 3) Griegs, 1945. 


the readings obtained on four standard thermometers. 
Woods Hole Oceanographic Institution produced a 
more elaborate twelve-thermometer tank in 1947 
which has heating and cooling elements controlled 
by Bourdon tube activated contacts.” A glass window 
and a movable telescope arrangement permit the 
thermometers to be read while submerged and com- 
pared against standard thermometers calibrated in 
0.01°C steps. Other tanks similar to the WHOI design 
are in use at the Pacific Oceanic Fisheries Investiga- 
tion, Honolulu, T. H.,2 and at the U.S. Bureau of 
Standards, Washington, D. C. 


2D. F. Bumpus and E.T. Penrose Equipment for Calibrating 
Deep Sea Reversing Thermometers (Woods Hole Oceanographic 
Institution, Ccmpletion Report No. 7) 1947. 


3H. Mann Plans and Specificaticns for a Constant Tempera- 
ture Tank for the Calibration of Deep Sea Reversing Thermom- 
eters (U.S. Fish and Wildlife Service, Pacific Ocean Fishing In- 
vestigations) (Unpublished manuscript) 23 May 1950. 


DESCRIPTION OF EQUIPMENT 


The new NEL calibration tank (fig. 1) represents 
an improvement over the earlier designs in that it 
provides automatic temperature control, very high 
accuracy, rapid operation, and a simplified method 
of taking readings. The NEL tank will also calibrate 
twenty-four thermometers at a time, or twice as many 
as possible in previous models. These thermometers 
may be moved into position after their temperature 


has equalized with that of the tank and read in situ 
by means of a reading telescope. The tank is well 
insulated from ambient temperatures so that little 
addition or subtraction of heat is necessary to main- 
tain temperatures within the desired limits of ac- 
curacy. The rate of heating and cooling is controlled 
precisely, permitting rapid large changes of tempera- 
ture, accurate microchanges of temperature, and 
maintenance of temperature within very small limits. 


Figure 1. Controlled-temperature calibration facility. 


Thermal System 


The calibration tank uses external hot and cold 
tanks, the former maintained well above and the 
latter well below operating temperature. The transfer 
of heat is accomplished by pumping liquid from either 
tank to the calibration tank, with a return path 
furnished to provide a closed circulating system 
(fig. 2). The choice of hot or cold is made by the 
thermostat, which controls electrically operated sole- 
noid valves on the two systems and the pumping 
motors. In addition, there is a metering valve in each 
system to control the rate of flow of hot or cold 
liquid so as to maintain constant tank temperature 
despite unavoidable transfers of heat to the sur- 
roundings. When a macrochange of temperature is 
desired, the metering valves are opened fully to 
permit rapid transfer of a considerable volume of 
liquid from either the hot or cold external tanks. The 
use of external tanks avoids the thermal lags which 
would occur if the heating and cooling systems were 
installed in the actual body of the calibrating tank 


STIRRING MOTORS 


HOT WATER 


METERING 
VALVES 
CALIBRATION TANK 


itself. In the initial installation one pump was used 
for both hot and cold tanks, but on the first trial run 
it was found that because of the residual hot or cold 
liquid in the pump itself and despite the very short 
piping system from it to the tank, there was too much 
overshooting. A pump and metering valve have now 
been installed on each tank so that when the thermo- 
stat demands hot or cold it is provided instantly at 
the requisite rate of flow to allow full mixing, with 
minimum of overshoot. 


Hot Tank 


The hot tank measures 8 by 10 by 20 inches and 
is made of brass sheet Ye-inch thick, brazed at all 
edges (fig. 3). It is thermally insulated with 1-inch 
cork board held in place and surfaced by 3-inch 
Permacel industrial tape which is painted to form 
a strong continuous surface. Water is piped into the 
whole system through the rear end of this tank. Two 
1500-watt, 110-volt heating elements are mounted 
in it through the front, together with a thermometer 


COLD WATER 
TANK 


SOLENOID CONTROL 
VALVES 


Figure 2. Circulating system. 


and a Bourdon tube thermostat to hold the tank 
temperature to within 2° of any desired value. The 
water is drawn from the center of the bottom of this 
tank to the circulating pump and returns from the 
calibration tank to the top, thereby maintaining a 
constant circulation as long as the solenoid value 
between the tank and the pump is open. The meter- 
ing valve is mounted in the pipeline between the 
pump and the calibration tank, as near the latter as 
feasible. The two heating elements are connected in 
series to enable the use of 220 volts for this 3000- 
watt heating system. 


Cold Tank 


The cold tank is also of brazed sheet brass con- 
struction, measuring 282 by 9'2 by 22 inches (fig. 3). 
The dimensions were dictated by the size requirements 
of a bank of three refrigerating coils known as 


THERMOMETER 
RETURN FLOW 


HOT TANK 


HEATING 
ELEMENTS 


HOT INFLOW 


COLD INFLOW 
THERMOSTAT 


METERING 
VALVE 


DRAIN VALVE 


Figure 3. 


needle coils, mounted in parallel to the expansion 
valves for speed of heat transfer. This tank is in- 
sulated in the same manner as the hot tank and 
mounted a few inches to the right of it, sharing the 
common circulation return with the hot tank. The 
cold liquid is drawn off the bottom of the tank, which 
is in the shape of a shallow pyramid. Circulation is 
controlled by the thermostat-operated solenoid valve 
and the manually controlled metering valve, both 
arranged as for the hot tank. 

All external piping, pumps, and valves are insu- 
lated with Prestite insulation which can be molded 
to fit any irregularities of form. A thermometer is 
mounted at the base of this tank and the compressor 
is controlled by a thermostat that can be set to hold 
the temperature of the liquid to within 2° from that 
of the room to —3°C. The compressor used is rated 
at 1.2 tons, and is mounted outside the building to 
provide sufficient air circulation for cooling. 


THERMOSTAT 
HOT TANK 
CONTROL 


COLD TANK 


THERMOMETER 


PUMP 


Thermal system. 


Calibration Tank 


The calibration tank is made with an inner lining 
of ¥-inch lucite, measuring 28 by 232 by 30 inches, 
backed by an aluminum foil for radiation insulation 
(fig. 4). Further heat insulation is provided by a 42- 
inch layer of tar-coated cork-board surrounding the 
inner lucite shell on all sides and at the top and 
bottom. This inner tank of lucite is supported evenly 
along its bottom on a grid of 2 x 4’s to prevent 
deformation and possible rupture by the weight of 


ste areeee, i - 
chip a | 


A. RACK BEFORE REVERSAL 


water (approximately 600 Ib) it contains when in 
operation. The outer shell is of Y2-inch plywood re- 
inforced at all angles by strength members. 


The whole tank is supported at the corners by 
tubular aluminum uprights, 3 inches in diameter with 
Y inch wall thickness. These are equipped with screw- 
adjustable feet for levelling purposes and extend 
to a height of 8 feet above the floor. Mounted on 
the top of each upright is a pulley assembly for the 
wire that raises and lowers the lid. 


Figure 4. Calibration tank, shown (A) before reversal of rack, (B) during reversal 


of rack, and (C) with rack removed. 


B. RACK BEING REVERSED 


TANK LID 


INDEXING 
DRIVE 


REVERSING DRIVE 
FOR RACK 


STIRRER 


THERMOSTAT 
SENSING ELEMENT 


CONSTANT-TENSION 
SPRINGS 

FOR TELESCOPE 
MOUNT 


CALIBRATION 
TANK 


C. TANK WITH RACK REMOVED 


Figure 4. (continued) 


Tank Lid 


The lid is built separately from the tank proper, 
though of similar construction as to insulation (fig. 
5). On it are two shock-mounted 1/20-hp motors 
connected by V-belt drive to two shafts, each passing 
into the tank through Micarta insulating inserts 12 
inches in diameter. A stainless steel four-bladed pro- 
peller is mounted on each shaft at diagonal corners 
of the tank to provide thorough cross-stirring of the 
tank liquid. Apertures in the lid are provided for 
a standard platinum resistance thermometer and for 
the thermostat sensing element. Two apertures are 
also provided for inserting leads for any other ele- 
ment that may be undergoing calibration. 

A motor and its accessory drive are mounted on 
the tank lid to permit reversing the thermometer rack 
with the lid closed. A motor is also provided for in- 
dexing the rack so that the thermometers may be 
read successively at the telescope. This latter drive 
includes a solenoid-controlled disengaging lock to 
enable the rack to be reversed. 


STIRRING 
MOTOR 


STIRRING 
SHAFT 


LEAD FOR 
RESISTANCE 
THERMOMETER 


LEAD FOR 
THERMOSTAT 
APERTURE FOR 
NSERTING LEADS 
RAISING AND 
LOWERING CABLE 


The under edge of the lid is fitted with a round 
soft rubber strip to form a seal between it and the 
upper lip of the tank proper, which is of '%2-inch 
Micarta. As can be seen, all controls are mounted 
on the lid of the tank, so that the only apertures 
beneath the surface of the liquid are those necessary 
for liquid transfer. 

The lid is raised and lowered by four 5/32-inch 
stainless-steel cables, one attached to each corner, 
passing over a pulley mounted on top of each up- 
right and down through its center. The cable is led 
by another pulley to two doubly grooved spiral 
drums mounted on the bottom of the tank, each of 
the two drums handling two of the cables. One drum 
is mounted on each end of the shaft of a reduction 
gear driven through a friction-slip clutch by a 1/6- 
hp motor. The direction of rotation of the motor is 
reversed for raising or lowering the lid. Limit switches 
are mounted at the top and bottom of the lid’s 
travel to prevent overrunning. Sets of rollers at each 
corner guide the lid and maintain it in strict align- 
ment with the four supporting uprights. 


MOTOR FOR 
INDEXING RACK 


MOTOR FOR 
REVERSING RACK 


STIRRING 
SHAFT 


STIRRING MOTOR 


RAISING AND 
LOWERING CABLE 


NEGATOR 
CONSTANT-TENSION 


SPRINGS 


Figure 5. Tank lid. 


Thermometer Rack 

The thermometer rack is circular. It is designed 
to hold 24 deep-sea reversing thermometers about 
its perimeter, each secured by a screw-adjustable 
rubber-faced cup at one end and a similar, spring- 
loaded cup at the other end (fig. 4). This is for 
speed and ease of mounting thermometers of various 
lengths. Provision is also made for mounting 24 sur- 
face thermometers between the deep-sea mounts. 
These fittings are attached to two Micarta disks, 
supported by a central shaft which can be rotated 
to bring each thermometer in front of the reading 
telescope by means of two vertical fingers projecting 
from circular plates mounted one on either end of 
the shaft. These are designed to engage a plate 
on the end of a drive shaft coming through the lid, 
which can be retracted by a solenoid to permit re- 
versal of the rack. Rack reversal is accomplished by 
mounting the rotating shaft in a framework sup- 


VERTICAL 
ADJUSTMENT 


CONTROL 
PANEL 


ported at the outer of its two vertical sides by ball 
and socket shafts, and by using bevel gears to drive 
the right-hand shaft. Power is supplied through the 
lid by a 1/20-hp reduction-gear motor on the top 
of the lid. The rack is supported by two vertical arms 
attached to the underside of the lid, the right one 
fitted with bearings for the reversing drive shaft 
and the left one with a limit switch to cut the drive 
motor when the rack is in a vertical position for 
locking onto the indexing drive. As can be seen, all 
gear in the tank is raised and lowered with the lid, 
making the rack easily accessible for loading or 
changing thermometers or for removal of the rack 
entirely when other apparatus is to be used in the 
tank. All fittings in the tank are of stainless steel. 


Tank Window 


The thermometers are read through a window 
mounted in the front side of the tank (fig. 6). This 


TANK WINDOW 


READING 
TELESCOPE 


HORIZONTAL 
ADJUSTMENT 


THERMOMETERS 
IMMERSED 
IN TANK 


Figure 6. Tank window, reading telescope, and control panel. 


window, which measures 9 by 19 inches, is a ther- 
mopane unit made to order by the Libby Owens 
Ford Glass Company and consists of four panes of 
Y4-inch, optically plane glass, opaque to infrared, 
mounted parallel in a metal-sealed frame. The three 
dead-air spaces between the panes give undistorted 
visibility with extremely low heat transfer. Twelve 
rubber-faced pressure screws hold the unit in place 
against an O-ring seated around a suitable aperture 
cut in the inner lucite shell of the tank. These screws 
are spaced evenly along its sides and upper and 
lower edges, and are mounted in aluminum brackets 
screwed to the frame of the tank. The frame for this 
window, which extends through the tank insulation, is 
made of wood with a removable rubber-lined inner 
frame, to give a snug positive fit for the thermopane. 


Reading Telescope 


To read the thermometers accurately, a reading 
telescope is provided. This is a 20X erecting instru- 
ment with horizontal hair at the principal focus of 
its eyepiece systems. It can focus to a minimum dis- 
tance of 10 inches, and at the 13-inch distance to 
the mounted thermometers its field is about 1 inch, 
which makes it possible to read the main and aux- 
iliary thermometers without moving it laterally. To 
assure accuracy, this telescope is held by a heavy 
frame, which moves laterally on ball bearings on 
two horizontal steel tubes pinned rigidly at either 
end to aluminum travelers. The telescope thus has 
a 4¥2-inch lateral traverse. The supporting travelers 
are in turn mounted on vertical steel rods on which 
they can be moved 18 inches vertically by means of 
rack and pinion gears. The mount may be locked 
in position in either of these movements by set screws 
actuated by means of knurled knobs. The supporting 
vertical rods are seated top and bottom in steel 
frames bolted to the front of the tank. This whole 
assembly is very carefully aligned so that the tele- 
scope is exactly perpendicular to the axis of the 
thermometers in all positions, thus eliminating error 
due to parallax, which is ordinarily the greatest 
single cause of error in reading thermometers from 
a distance. The thermometers themselves are held 
rigidly vertical when their rack is locked in reading 
position. The 7-pound weight of the telescope as- 
sembly is counterbalanced by two constant-tension 
negator springs so that it will remain in any desired 
position. 


10 


TEMPERATURE CONTROL UNIT 


Thermostat 


Temperature control is attained by means of a 
thermostat using two thermistor beads, one on each 
side of a resistance bridge (fig. 7). The other two 
sides of the bridge consist of a fixed resistor and a 
Helipot. The thermistor beads are mounted 3 inches 
to the left and at the same level as the thermometers 
to be calibrated. As temperature change occurs the 
resistance of the thermistors varies, throwing the 
bridge out of balance. This imbalance is fed to a 
dc amplifier. The amplified voltage drives a servo 
motor either clockwise or counterclockwise, depend- 
ing on the sign of imbalance. The servo, in turn, 
drives a cam mounted on a slip clutch that closes 
either of two microswitches. However, when exact 
balance is attained neither of the two switches (one 
controlling the hot and the other the cold transfer 
pumping system) is actuated. 

At full gain, this temperature-control system re- 
sponds more rapidly than can be measured with 
either the platinum or mercury thermometers. 


Control Panel 


The control panel is mounted on the left front 
supporting member of the tank. It can be swung into 
position for operation either by the thermometer 
reader at the telescope or by the operator at the 
temperature controls on the left (fig. 6). The panel 
contains the main power switch and controls for 
tank illumination, thermostat, pump, lid raise and 
lower, front and back stirrers, indexing and revers- 
ing. The temperature controls are necessarily on the 
panel of the thermostat, accessible to the operator 
of the temperature-measuring bridge. Illumination 
of the tank through the lucite inner wall is supplied 
by two fluorescent tubes mounted in recesses, one 
on each side of the thermopane. 

The final standard of temperature is obtained by 
means of a Leeds and Northrup platinum resistance 
thermometer and associated Muller Bridge, Type 
G-2, calibrated by the U.S. Bureau of Standards. 
This bridge measures resistance to 0.0001 ohm, the 
maximum correction given by the U.S. Bureau of 
Standards, thus enabling temperatures to be read 
to 0.001°C absolute. The manufacturer of the bridge 
claims an over-all accuracy only within several thou- 
sandths of a degree centigrade. However, in the 


THERMOSTAT 


GALVANOMETER 


RESISTANCE 
BRIDGE 


Figure 7. Thermostat and resistance bridge. 


uses for which the tank was designed the bridge 
will be used only between 25 and 30 ohms and it 
is safe to assume that temperatures can be measured 
to an accuracy of +0.002. The bridge is periodi- 
cally checked against a standard 10.0100-ohm re- 
sistor, certified by the Bureau of Standards, and over 
a period of three years there has been no measur- 
able divergence from this standard. 

In addition the standard thermometer is checked 
periodically against the ice point provided by dis- 
tilled water ice. 


CALIBRATION OF REVERSING 
THERMOMETERS 


Although the tank can be used to calibrate any 
instrument capable of being inserted into it, it is 
largely used for reversing thermometers. The step- 
by-step procedure used in reversing-thermometer 
calibration is presented here. 


Step 1: Fill Tanks 


The system is first filled with water to which is 
added 15 gallons of alcohol. This amount of alcohol 
permits temperatures to be lowered to —3°C with- 
out ice forming on the refrigerating coils. The solu- 
tion is checked periodically with an alcohol hydrom- 
eter and more is added as needed to replace that 
lost by evaporation. Alcohol was chosen as being 
the simplest and cleanest antifreeze to use, as well 
as the least expensive. 


Step 2: Set Temperature 

Ordinarily the desired temperature is dialed on 
the thermostat the night before calibration work is 
to start. The whole system is then put on a time 
switch, so that it will be at working temperature in 
the morning. 

For the highest speed of operation, the calibrating 
run is usually started at the lowest temperature de- 
sired and then increased through the necessary range. 


11 


The change is very rapid for calibration steps of 1 
to 5 degrees because of the large reserves of hot 
and cold water available instantly on demand. The 
hot tank contains 7 gallons maintained at 80°C, 
and the cold tank 25 gallons maintained at —3°C. 


Step 3: Insert Thermometers 


Twenty-four thermometers are mounted in the cir- 
cular rack and the whole lid is lowered, so that the 
thermometers are wholly immersed and the aperture 
sealed. The stirrers are then placed in operation to 
give very rapid mixing of the water mass and as 
nearly homogeneous a temperature structure as is 
possible. 

When the desired temperature has been attained, 
the metering valves are adjusted to make the flow 
of water from the hot or cold tanks exactly compen- 
sate for unavoidable transfer of heat from the tank 
because of ambient differences of temperature. An 
extremely small aperture is needed to avoid over- 
shooting because of the slight lag in the thorough 
mixing of the incoming water with the whole water 
mass. Metering is made possible by the use of cen- 
trifugal pumps which act as their own bypasses when 
the flow is shut down. This system was found to be 
simpler and more readily controlled than that of 
varying the speed of the motors driving the pumps, 
which was tried at one stage of construction. 


Step 4: Reverse Thermometers 

Ordinarily the thermometers are left for 10 minutes 
at a given temperature to assure full equalization. 
During this period the bridge operator constantly 
watches the galyanometer spot. If the spot varies 
more than 1 mm (i. e., 0.001°C) from its null, the 
operator makes the necessary adjustments of the 
metering valyes. Several minutes of stabilization are 
required after each temperature change. 

After the temperature has remained constant for 
the required period, the operator at the controls 
reverses the rack so that it locks in the reading posi- 
tion. If the mercury columns in any of the thermom- 
eters are found not to have broken, the lid may be 
raised a few inches and the rack tapped sharply 
without changing the temperature appreciably. 


Step 5: Read Thermometers 


The operator at the telescope can now read the 
main thermometer of each unit successively by oper- 


12 


ating the indexing mechanism which rotates the rack 
to move successive thermometers into reading posi- 
tion, either clockwise or counterclockwise. There is 
a 7-second pause between moves, which is usually 
sufficient for reading. 

There ordinarily is no need to read the auxiliary 
thermometer because the surrounding bath is main- 
tained at constant temperature by the operator at 
the temperature controls. Of course, if required, 
calibration can be established for auxiliary ther- 
mometers at the same time. This is done by having 
both operators read the thermometers. Then the 
whole process is repeated twice at the same tem- 
perature, resulting in three double checks at each 
temperature check. This is not only a check on accu- 
racy, but also gives a very good evaluation of the 
dependability of the individual thermometers. 

Since the thermometers are read at the same tem- 
perature at which they were reversed there is no 
need to go through the tedious temperature correc- 
tion required when they have to be removed from 
the bath and allowed to reach a steady room tem- 
perature, which in itself usually takes at least 30 
minutes. 

No time is lost waiting for thermometers to equal- 
ize after they have been reversed. And, of course, 
there is no correction for thermal expansion of the 
mercury. The index correction is read directly, thus 
saving time and possible errors. 

It is estimated that with two experienced oper- 
ators it is possible to calibrate a set of twenty-four 
thermometers in two days, depending upon the range 
of the thermometers and the number of points (usu- 
ally every 2°C) to be read. Thus, the tank enables 
thermometers to be calibrated accurately and surely 
against a known standard in about one-fifth the 
time previously required and with about one-fifth 
of the labor. 


CONCLUSIONS 


Preliminary use and evaluation of the temperature- 
controlled tank indicate that if gives an accuracy 
of +0.002°C over a range of temperatures from 
—3°C to 40°C and provides great savings of time 
and effort in calibration of reversing thermometers. 

The accuracy is dependent upon the reliability of 
the Leeds and Northrup platinum resistance thermom- 
eter, the Muller bridge, and the thermostat. The 
system is checked periodically for ice point and the 


bridge is checked against a standard 10-ohm re- 
sistance. 

The main time consumed is in allowing the ther- 
mometers to come to equilibrium at each new tem- 
perature at which a calibration is required. In making 
macrotemperature changes, a constant increase of 
12°C/hr with 3000 watts in the heating element 
and a decrease of 8°C to 12°C/hr are possible. This 
latter change becomes slower as the tank tempera- 
ture approaches that of the external tank. 

Thermometers may be aligned and read rapidly. 


RECOMMENDATIONS 


1. Continue development to include installation of 
electronic time-proportioning switches in metering of 
heat transfer. 

2. Study the possibility of an instrument to record 
temperatures at two points in the tank, throughout 
any operation. 


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Chief, Bureau of Ships (Code 312) (12 copies) 

Chief, Bureau of Ordnance (Re6) (Ad3) (2) 

Chief, Bureau of Aeronautics (TD-414) 

Chief of Naval Operations (Op-37) (2) 

Chief of Naval Research 
(Code 416) (Code 466) 

Commander in Chief, U.S. Pacific Fleet 

Commander in Chief, U.S. Atlantic Fleet 

Commander Operational Development Force, U.S. 
Atlantic Fleet 

Commander, U.S. Naval Air Development Center 
(Library) 

Commander, U.S. Naval Air Missile Test Center 
(Technical Library) 

Commander, U.S. Naval Air Test Center (NANEP) (2) 

Commander, U.S. Naval Ordnance Laboratory 
(Library) (2) 

Commander, U.S. Naval Ordnance Test Station 
(Pasadena Annex Library) 

Commanding Officer and Director, David Taylor 
Model Basin (Library) (2) 

Commanding Officer and Director, U.S. Navy 
Underwater Sound Laboratory (Code 1450) (3) 

Director, U.S. Naval Engineering Experiment 
Station (Library) 

Director, U.S. Naval Research Laboratory (Code 
2021) (2) 

Director, U.S. Navy Underwater Sound Reference 
Laboratory (Library) 

Commanding Officer, Office of Naval Research, 
Pasadena Branch 

Hydrographer, U.S. Navy Hydrographic Office (1) 
(Air Weather Service Liaison Office) (1) 
(Division of Oceanography) (1) 

Senior Navy Liaison Officer, U.S. Navy Electronics 
Liaison Office 

Superintendent, U.S. Naval Postgraduate School 
(Library) (2) 

Assistant Secretary of Defense (Research and 
Development) (Technical Library Branch) 


NAVY — NEL San Diego, Calif. 


INITIAL DISTRIBUTION LIST 


(One copy to each addressee unless otherwise specified) 


Assistant Chief of Staff, G-2, U.S. Army (Document 
Library Branch) (3) 

Chief of Engineers, U.S. Army (Engineer Research 
and Development Division, Field Engineering 
Branch) 

The Quartermaster General, U.S. Army (Research 
and Development Division, CBR Liaison Officer) 

Commanding General, Redstone Arsenal 
(Technical Library) 

Commanding Officer, Transportation Research and 
Development Command (TCRAD-TO-1) 

Chief, Army Field Forces (ATDEV-8) 

Resident Member, Beach Erosion Board, Corps of 
Engineers, U.S. Army 

Commander, Air Defense Command 
(Office of Operations Analysis, John J. Crowley) 

Commander, Air University (Air University Library, 
CR-5028) 

Commander, Strategic Air Command 
(Operations Analysis) 

Commander, Air Force Armament Center (ACGL) 

Commander, Air Force Cambridge Research Center 
(CRQST-2) 

Executive Secretary (John S. Coleman), Committee 
on Undersea Warfare, National Research Council 

Commandant, U.S. Coast Guard (Aerology and 
Oceanography Section) 

Commander, International Ice Patrol, 

U.S. Coast Guard 
Director, U.S. Coast and Geodetic Survey 
U.S. Fish and Wildlife Service, Pacific Oceanic 

Fishery Investigations (Library), Honolulu 
U.S. Fish and Wildlife Service, La Jolla, California 

(Dr. E. H. Ahlstrom) 

(South Pacific Fishery Investigations, John C. Marr) 
Brown University, Director, Research Analysis Group 
University of California, Director, Marine Physical 

Laboratory, San Diego, California 


University of California, Director, Scripps Institution 
of Oceanography (Library), LaJolla, California 
The Johns Hopkins University, Director, Chesapeake 

Bay Institute (Library), Annapolis, Maryland 
Massachusetts Institute of Technolog 
Director, Acoustics Laboratory eka A. Kessler) 
University of Miami, Director, Marine Laboratory 
University of Southern California, Department of 
Geology (K. O. Emery) 
Agricultural and Mechanical College of Texas, Head, 
Department of Oceanography (Dr. D.F. Leipper) 
The University of Texas ; 
Director, Defense Research Laboratory j 
University of Washington, Department of Oceanog- 
raphy (Dr. R.H. Fleming, Executive Officer) 
(Fisheries-Oceanography Library) 
Yale University 
Director, Bingham Oceanographic Laboratory 
Director, Lamont Geological Observatory (M. Ewing) 
The Director, Woods Hole Oceanographic Institution 
Vitro Corporation of America, Silver Spring 
Laboratory (Library)