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PART 3

MERCURY DIFFERENTIAL MANOMETER
AND ELECTRONIC LOGS

 


18
DESCRIPTION
 
A. GENERAL DESCRIPTION
 
18A1. General. The mercury differential manometer underwater log (Figure 18-1) is made by the Pitometer Log Corporation, New York, New York. This type of underwater log derives its name from the fact that hydraulic pressures actuate a column of mercury in a mercury manometer. The movement of the column of mercury, caused by dynamic pressure from the rodmeter, is the actuating force that operates the system. This system consists of the following components: rodmeter, sea valve, manometer, transmitter, master speed repeater, speed and distance repeater, and a mileage indicator.

18A2. Rodmeter. (See Figure 18-1.) The rodmeter, commonly called the sword, is located in the forward torpedo room or in the pump room below the light draft water line. This rodmeter is identical with the rodmeter used with the Pitometer rotary balance type log. It projects through the hull of the ship into the water and is the unit in which static and dynamic pressures are produced and transmitted to the mercury differential manometer. When in use, the rodmeter extends outside the hull for a distance of approximately 2 feet. Being located in the forward part of the ship, the rodmeter contacts water least disturbed by the movement of the ship.

18A3. Sea valve. (See Figure 18-1.) The sea valve provides a means of closing the opening through which the rodmeter passes when it is withdrawn or raised to its fully secured position. The sea valve is located in the forward torpedo room beneath the deck. In some of the earlier ships, it is located in the forward part of the pump room. A tube connects the spigot and flange on the underside of the sea valve assembly with the outer hull, where it is welded to, a flange and guide bushing. The guide bushing forms the lower support for the rodmeter. A valve extension is mounted on top of the sea valve and forms an upper support for the rodmeter. A packing

  gland is mounted on the valve extension to provide a leakproof seal between the rodmeter and the sea valve.

18A4. Mercury differential manometer. (See Figure 18-1.) The mercury differential manometer is a U-tube of special design, containing mercury. It is mounted in gimbals so that the assembly will tend to remain in a vertical position regardless of the roll and pitch of the ship. The two larger outer tubes of the manometer are connected at their base. A small central tube connects this base with a float chamber in which the mercury rises and falls with changes in the ship's speed. The top of the float chamber opens into a gear chamber which is connected to, the upper or static line from the rodmeter. Dynamic pressure from the rodmeter is hydraulically transmitted to the lower nipple of the manometer which is connected through piping to both side tubes. A hard rubber float filled with mercury supports a bronze gear rack which is meshed with a gear on the shaft in the gear chamber. The shaft extension extends out of the gear chamber cover through a grease seal gland. Hose nipples, vent cocks, a bypass valve, and shutoff cocks are mounted in the hydraulic lines connecting the rodmeter with the mercury columns.

18A5. Transmitter. (See Figure 18-1.) The transmitter is mounted in an aluminum case which is secured to the manometer gear chamber. A distance integrator cam and the speed dial are mounted as a unit on the mainshaft, which is coupled to the shaft extension of the manometer. The speed dial is positioned directly by the mercury in the float chamber, and will indicate the ship's speed in knots without electrical connections. This speed indication is transmitted to the master speed repeater, or in some cases to speed repeaters only, by a self-synchronous transmitter. Distance is obtained from the speed element by means of a time-controlled mechanical

 
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Figure 18-1. Components of mercury differential manometer underwater log system.
Rodometer and sea valve located in forward torpedo room or pump room.
Mercury manometer and transmitter located in forward torpedo room or pump room.
Mileage indicator located in control room.
Speed and distance repeater located in conning tower.
Master speed repeater located in control room.
Figure 18-1. Components of mercury differential manometer underwater log system.
 
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integrator. The time element for the integrator is introduced by a constant speed synchronous motor, or by a direct current motor which is controlled by an accurate clock movement. The motor is mounted on the back of the motor base plate. The integrator mechanism operates the distance counter which registers nautical miles and tenths of a mile. The turning of the countershaft operates contact points which make and break the electrical circuit to the distance repeaters (magnetic counters) located in the speed and distance repeater, and in the mileage indicator.

18A6. Master speed repeater. (See Figure 18-1.) The master speed repeater is located in the control room. Its functions are: (1) to receive speed indications from the self-synchronous transmitter in the transmitter; (2) to convert these indications from the irregularly spaced speed dial of the transmitter (Figure 18-4) to a uniformly spaced dial (Figure 18-9); (3) to transmit these speed indications to the speed and distance repeater, the gyro speed corrector, and the torpedo data computer. The interior mechanism is mounted on a plate which is removable from the case so that the complete unit may be removed for purposes of inspection and tests. The self-synchronous repeater in this unit receives speed indications from the self-synchronous transmitter in the transmitter case. The self-synchronous repeater in the master speed repeater actuates a follow-up motor which

  drives a cam, thereby positioning a speed pointer. The speed pointer shaft actuates a self-synchronous transmitter which transmits speed indications to the speed and distance repeater in the conning tower, the gyro speed corrector, and the torpedo data computer.

18A7. Speed and distance repeater. (See Figure 18-1.) The speed and distance repeater is located in the conning tower. The function of this unit is to indicate speed received from the self-synchronous transmitter of the master speed repeater. Distance indications are received by an alternating current electromagnet from the impulses of the contacts in the transmitter case. This electromagnet operates a distance counter which records distance indications in units of 1/10 mile. In earlier ships the electromagnet is direct-current operated.

18A8. Mileage indicator. (See Figure 18-1.) The mileage indicator is located in the control room. The function of this unit is to receive and record distance indications from the transmitter mechanism.

18A9. Constant frequency supply. Some installations of the mercury differential manometer underwater log system include another unit known as the constant frequency supply unit. The function of this unit is to supply a constant 60-cycle 115-volt current to the synchronous motor in the transmitter, and to the synchronous motors in the shaft revolution indicators.

 
B. DESCRIPTION OF OPERATION
 
18B1. Hydraulic pressures. While the ship is stationary, the water pressures in the rodmeter tubes are equal (static pressure only), and the mercury columns in the manometer are at equal heights. As soon as the ship gets underway or increases speed, the forward motion creates additional pressure through the dynamic (forward) orifice in the rodmeter, while the pressure through the static orifices remains the same. This causes the center mercury column in the manometer to rise, thereby operating the system.

18B2. Mercury differential manometer. (See Figures 18-2 and 18-3.) The lower nipple of

  the mercury manometer piping is hydraulically connected to the dynamic line from the rodmeter, while the upper central section of the manometer is connected to the static line from the rodmeter. The static pressure on top of the center mercury column remains the same. As the dynamic pressure increases, due to the forward movement of the ship, it is transmitted to the side mercury columns. This extra pressure (dynamic) causes the mercury column to rise in the float chamber. The hard rubber float supporting a gear rack in the gear chamber rises with the mercury and actuates the transmitter mechanism. A few ships have
 
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Figure 18-2. Front view of manometer and transmitter.
1. STATIC LINE
2. DYNAMIC SHUT-OFF VALVE
3. DYNAMIC VENT COCK
4. STATIC VENT COCK
5. STATIC SHUT-OFF VALVE
6. DYNAMIC LINE
7. BY-PASS VALVE
8. TRANSMITTER CASE
9. GEAR CHAMBER
10. SPEED DIAL
11. DISTANCE COUNTER
12. FLOAT CHAMBER
13. MANOMETER CENTER TUBE
14. MANOMETER SIDE TUBES
Figure 18-2. Front view of manometer and transmitter.
  Figure 18-3. Installation of float and gear rack.
1. STATIC LINE
2. DRIVEN GEAR
3. ROLLER ARM SPRING
4. GEAR CHAMBER
5. GEAR RACK
6. DYNAMIC LINE
7. GIMBAL RING
8. FLOAT CHAMBER
9. FLOAT
10. MANOMETER SIDE TUBES
11. MANOMETER CENTER TUBE
Figure 18-3. Installation of float and gear rack.
 
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Figure 18-4. Transmitter, cover removed.
1. DISTANCE COUNTER
2. POINTER
3. SQUARE FUNCTION SPEED DIAL
4. OPERATING ARM FOR TIMING COUNTER
5. ESCAPEMENT
6. TIMING COUNTER
7. INTEGRATOR WHEEL BRAKE
8. INTEGRATOR WHEEL
9. INTEGRATOR DRIVING PAWL
10. INTEGRATOR ARM
11. INTEGRATOR CAM
12. SELF-SYNCHRONOUS SPEED TRANSMITTER
13. STAR WHEEL
14. REPEATER CONTACTS

Figure 18-4. Transmitter, cover removed.
 
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a spiral gear assembly instead of the conventional circular gear. The spiral gear is designed to spread the dial graduations at the low-speed end of the dial.

Figure 18-5. Sixty-cycle alternating current integrator
timing assembly, cover removed.
Figure 18-5. Sixty-cycle alternating current integrator timing assembly, cover removed.

18B3. Transmitter. The movement of the float in the float chamber is transmitted to the mainshaft of the transmitter mechanism. This mainshaft carries the distance integrator cam and the master speed dial assembly. The speed dial (Figure 18-4) is positioned directly by the movement of the mercury in the float chamber and indicates the ship's speed in knots without electrical connections. Through gearing, the mainshaft operates a self-synchronous transmitter which transmits speed indications to a self-synchronous repeater in the master speed repeater. On ships not having a master speed repeater, the speed indications are transmitted directly to the speed indicator in the speed and distance repeater. Distance is obtained from the speed element by a mechanical integrator in the following manner: A synchronous motor operating on controlled 60-cycle, 115-volt alternating current, turns a shaft at a speed of 60 revolutions per minute. This shaft is geared, in a ratio of 15 to 1, to a spur gear under the clock plate cover. The spur gear (Figure 18-5) has a cam groove cut in its face, and a roller in this groove swings

  an operating cam through an arc of approximately 20 degrees every 15 seconds, or 240 strokes per hour. A timing counter (Figure 18-6) registers the number of strokes of the operating arm, and provides a means of checking the operation of the integrator unit. The operating arm is mechanically connected to the integrator arm by a spring-loaded integrator link. The lower end of the integrator arm carries a knife-edge which strikes the distance integrator cam when the arm is pulled over by the action of the operating arm and link. The distance integrator cam is so designed that the angle through which the integrator arm moves to strike the cam every 15 seconds is directly proportional to the speed of the ship. For example, the faster the speed of the ship, the longer the sweep of the integrator arm will be every 15 seconds, while at zero knots the knife-edge just clears the tip of the cam, and cannot swing at all (see inset, Figure 18-6). A tension spring inside the integrator link allows the operating arm to move when the integrator arm is restrained by the cam. A pawl mounted on the integrator arm drives the integrator wheel in a clockwise direction (Figure 18-7). A stop pawl mounted at the upper left side of the integrator wheel prevents the wheel from turning in a counterclockwise direction. A brake engages the upper right side of the integrator wheel to keep it from jumping ahead when the knife-edge strikes the cam. The integrator wheel drives a shaft which operates the master distance counter (Figure 18-8). This counter registers nautical miles and tenths; one complete revolution of the shaft of the counter being equivalent to one mile. A ten-tooth star wheel, mounted on the end of the shaft of the counter, operates electrical contacts. One contact is made and broken each tenth of a mile, and the resulting electrical impulse is transmitted to the electromagnet-operated counters in the speed and distance repeaters, and in the mileage indicator.

18B4. Master speed repeater. (See Figure 18-9.) The shaft of the self-synchronous repeater in the master speed repeater is

 
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Figure 18-6. Integrator cam at 15-knot and zero-knot positions.
1. DISTANCE COUNTER
2. INTEGRATOR CAM
3. OPERATING ARM
4. TIMING COUNTER
5. INTEGRATOR WHEEL
6. INTEGRATOR ARM
7. STOP BRACKET
8. INTEGRATOR ARM KNIFE-EDGE
9. SELF-SYNCHRONOUS SPEED TRANSMITTER
10. STAR WHEEL
11. REPEATER CONTACTS

Figure 18-6. Integrator cam at 15-knot and zero-knot positions.
 
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Figure 18-7. Integrator wheel control mechanism.
1. STOP PAWL
2. INTEGRATOR LINK ASSEMBLY
3. WHEEL BRAKE
4. INTEGRATOR WHEEL
5. INTEGRATOR ARM
6. WHEEL DRIVING PAWL
7. COUNTERSHAFT
Figure 18-7. Integrator wheel control mechanism.

Figure 18-8. Distance repeater contacts installed.
1. DISTANCE COUNTER
2. DRIVEN SPIRAL GEAR
3. STAR WHEEL
4. CONTACT POINTS
5. UPPER CONTACT SPRING
6. LOWER CONTACT SPRING
Figure 18-8. Distance repeater contacts installed.

  electrically positioned by the self-synchronous transmitter in the transmitter mechanism. A heart-shaped cam assembly (Figure 18-10) is mounted on the repeater shaft extension, and actuates a pivoted arm which in turn operates electrical contacts. A roller which normally rides in the lowest part of this cam (Figure 18-11) is mounted on one end of a pivoted arm which has the center contact assembly mounted on the other end of the arm. A spring holds the roller in contact with the heart cam at all times. For normal changes in speed, the roller will maintain its position in the low spot of the cam as shown at the top center of Figure 18-11. For sudden abnormal changes in speed, the roller may be momentarily forced out of its normal position as shown at the left in Figure 18-11, but the spring will return the roller to the low point when the follow-up motor drives the follow-up contact assembly, and with it, the center contact assembly, to the proper position.

The follow-up contact assembly is driven through the same number of degrees as the heart cam without imposing any appreciable load on the self-synchronous repeater. Likewise, the use of the heart cam prevents the excessive load on the self-synchronous repeater which would result if the repeater armature were restrained from following the speed transmitter during abnormal speed changes.

The center contact assembly normally stands with both spring contacts touching the contact screws of the follow-up contact assembly (Figure 18-12). As the center contact moves, it opens one of the two contacts that control the shading coil circuits of the follow-up motor through slip ring and brush assembly. This motor will run in either direction, depending on which contact is opened by the action of the heart cam. When the heart cam is stationary, both shading coils are energized, holding the motor stationary.

The follow-up motor drives a worm gear (Figure 18-11) which carries the follow-up contact assembly. The worm gear is mounted on a shaft, the other end of which carries a pointer cam which raises and lowers a carriage

 
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Figure 18-9. Master speed repeater, cover removed.
Figure 18-9. Master speed repeater, cover removed.
slide. This carriage slide has a gear rack on one side which engages the pointer shaft gear (Figure 18-10).

The pointer shaft gear is mounted on the pointer shaft extension of the self-synchronous transmitter. The pointer cam will always turn through the same number of degrees as the heart cam (and hence the same number of degrees as the square low-speed dial of the transmitter mechanism) for a given speed change. However, the pointer cam is so designed that the carriage slide will move

  with a linear function as the cam rotates with its square low function. As the pointer cam moves the carriage slide upward or downward, the pointer shaft extension of the self-synchronous transmitter is turned, the pointer is positioned to indicate speed in knots on the linear dial and the linear speed indications are electrically transmitted to the speed and distance repeater.

18B5. Speed and distance repeater. (See Figure 18-13.) The self-synchronous repeater in the speed and distance repeater is electrically

 
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Figure 18-10. Master speed repeater, pointer and dial removed.
1. SELF-SYNCHRONOUS SPEED TRANSMITTER
2. GEAR RACK
3. CARRIAGE GUIDE ROD BRACKET
4. CARRIAGE GUIDE RODS
5. POINTER SHAFT GEAR
6. CAM ROLLER CARRIAGE
7. CAM ROLLER
8. POINTER CAM
9. ROLLER ARM ASSEMBLY
10. BRUSH ASSEMBLY
11. FOLLOW-UP CONTACT ASSEMBLY
12. HEART CAM
13. SELF-SYNCHRONOUS SPEED REPEATER
14. FOLLOW-UP MOTOR
15. CONDENSERS 0.5-MICROFARAD
16. RESISTOR, 100-OHM

Figure 18-10. Master speed repeater, pointer and dial removed.
connected to the speed transmitter in the master speed repeater, and repeats speed indications of this transmitter. The distance counter is electrically operated by an a.c. electromagnet which receives its electrical impulses from the contact assembly in the transmitter case. Some ships have d.c. electromagnets operating the distance counter. In some ships the speed repeater has a square function (unevenly spaced) dial (Figure 18-4), and is controlled by the self-synchronous transmitter in the transmitter case. Some of these ships have a master speed repeater which was later installed in order to provide   a uniformly spaced dial for use with the torpedo data computer.

18B6. Mileage indicator. The mileage indicator electrically repeats the distance indications of the transmitter mechanism. A six-figure, reset-type counter indicates units of 1/10 nautical mile. The counter is operated by an a.c. electromagnet which receives an impulse every 1/10-mile from the contact assembly in the transmitter case in the same manner as distance is registered on the speed and distance repeater.

 
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Figure 18-11. Heart cam, with roller in normal and abnormal positions.
1. HEART CAM
2. CENTER CONTACT ASSEMBLY
3. PIVOTED ARM
4. ROLLER SPRING
5. ROLLER
6. HEART CAM NOTCH
7. WORM SHAFT GEAR
8. WORM SHAFT
9. CAM DRIVING WORM
10. FOLLOW-UP CONTACT ASSEMBLY
11. SIDE CONTACTS
12. CAM SUPPORT BRACKET
13. BRUSH ASSEMBLY
14. WORM GEAR

Figure 18-11. Heart cam, with roller in normal and abnormal positions.
 
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Figure 18-12. Follow-up contact assembly operating positions.
NORMAL POSITION (NO SPEED CHANGES)
BOTH SIDE CONTACTS ARE BARELY CLOSED, WITH APPROX. 0.010 inch CLEARANCE BETWEEN CONTACT SPRING AND CENTER ARM INSULATION. A MOTION OF 0.003inch-0.004inch OF THE CENTER ARM SHOULD DISCONNECT ONE OF THE SIDE CONTACTS

ACTUATED POSITION (SPEED CHANGING)
ONE SIDE CONTACT OPEN. CLOSED CONTACT ENERGIZES PROPER SHADING COIL CIRCUIT OF THE FOLLOW-UP MOTOR UNTIL SPEED CHANGE IS COMPLETED
Figure 18-12. Follow-up contact assembly operating positions.
 
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Figure 18-13. Speed and distance repeater removed from case.
Figure 18-13. Speed and distance repeater removed from case.
 
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