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12
LOG AND SHAFT REVOLUTION SYSTEMS
 
A. ROTARY CONVERTER AND CONSTANT FREQUENCY CONTROL UNIT
 
12A1. Description. The purpose of the constant frequency control unit is to control the speed of rotation of a rotary converter, primary 120-volt d.c., secondary 115-volt, 60-cycle, a.c., and maintain the frequency of the output at exactly 60 cycles for operation of the log and shaft revolution indicator system.

There are two types of constant frequency control units in use, one made by the Pitometer Log Corporation and the other by the Electric Tachometer Corporation. Both units operate on the principle of an electrically driven tuning fork, and are similar in construction. The 60-cycle tuning fork is the prime source of constant frequency.

The rotary converter converts 120-volt direct current to 115-volt, 60-cycle alternating current. This converter, together with the frequency control unit, supplies the constant frequency 60-cycle current necessary for the operation of the synchronous motor in the propeller shaft revolution indicators.

The converter is compound wound with a separate field lead brought out for connection to the rheostat in the constant frequency control unit. The machine is of drip-proof construction arranged for overhead mounting.

The converter has a 4-pole armature designed for rotation at 1800 rpm. The field is of 4-pole cast iron construction. Another winding on the field is connected to an external resistance.

A centrifugal governor is connected in such a manner that with no external field resistance it regulates the speed of the inverted rotary converter to about 1775 rpm. When the speed of the inverted rotary converter is increased to 1800 rpm by means of field resistance, the contacts of the governor remain closed and the speed control rests with the external resistance in the constant frequency control unit.

  12A2. Operation of Electric Tachometer Corporation type unit. The controlled frequency power is obtained from the a.c. output slip rings of a rotary converter and energizes the lower of 2 synchronous motors in the frequency control unit. One side of a mechanical differential is driven in synchronous relation with the converter output frequency by this lower synchronous motor. The other side of the differential is driven in a reverse direction at constant speed by the top synchronous motor. Constant frequency power for this top motor is obtained from a vacuum tube amplifier and its associated tuning fork which is adjusted to vibrate at exactly 60 cycles. Thus, the 60-cycle tuning fork is the prime source of constant frequency which it generates in coils nearest the weighted ends and impresses on the amplifying tube. The fork and amplifier work together; the tuning fork vibrates independently at its own natural frequency and the amplifier keeps the fork vibrating by feeding back some output power. Most of the amplifier power output goes to rotate the top motor at a constant speed corresponding to the frequency of the fork.

A spider arm is operated by the action of the differential and this arm operates a rheostat to control the field current of the inverted rotary converter. The action which takes place is as follows:

When the top and lower motors are running at the same speed, there is no motion of the differential spider arm. This condition exists only when the converter output frequency is the same as, the fork frequency. If the converter falls below synchronous speed, the decreased speed of the lower motor and its half of the differential starts the spider arm revolving. The spider arm turns the arm of the rheostat. The change in position of the rheostat arm changes the converter field current so that the speed and output frequency of the converter are restored to synchronism with the tuning fork. The frequency of the converter output is thus effectively locked

 
160

Figure 12-1. Schematic diagram of constant frequency control unit.
Figure 12-1. Schematic diagram of constant frequency control unit.
in synchronism with the tuning fork frequency. This condition is true in spite of changes in load on the converter, temperature-resistance changes in the windings, or +- 10 percent variation in the d.c. voltage supply to the converter.   A stroboscope disk, driven by the top motor at tuning fork frequency, gives visual indication of a gain or loss in converter speed. Normally the radial lines of the stroboscope disk appear to be stationary because the flashes of light from
 
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Figure 12-2. Frequency control unit, Pitometer Log Corporation type.
Figure 12-2. Frequency control unit, Pitometer Log Corporation type.
 
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the stroboscope lamp connected to the output frequency are in synchronous relation to the constant speed of the disk. If the converter gains or loses, the change in the rate of flashes creates the illusion of turning of the disk. At the same time, the differential spider arm does actually turn, due to the changed speed of the lower motor. If for any reason the apparatus fails to correct the change in speed, an alarm is energized to show that the unit has lost control. The stroboscope disk is intended as a relative check of converter and fork frequency. A clock is provided as a means of checking the absolute or real value of the converter frequency. When the generated output frequency is 60 cycles, the hand of the clock makes 1 revolution per   minute. When the stroboscope disk shows that the converter is in synchronism, the clock serves as a check on the fork. The operation of the Pitometer Log Corporation control unit is identical, except that the tuning fork is started by a magnet and clapper controlled by the line switch. The units are described in detail in the manufacturer's instruction book.

12A3. Maintenance. It is necessary that the brushes and commutator of the converter be kept clean and the brushes set for minimum sparking under normal load. Detailed maintenance instructions for bearings, gears, and tubes may be found in the manufacturer's instruction book.

 
B. UNDERWATER LOG SYSTEM
 
12B1. Description. The underwater log system consists of the equipment required for indicating the speed of the submarine and the distance traveled through the water. Each of the various types of underwater log systems in service requires a rodmeter which projects out through the pressure hull of the submarine, and mechanisms for converting into a speed indication the differences between the dynamic pressure of the water caused by the forward motion of the ship, and the surrounding static pressure. Each of the systems also has a mechanism for integrating speed with respect to time to indicate the total distance traveled. The system requires 115-volt, 60-cycle, single-phase, alternating current for operation and is designated as circuit Y.

The mechanical and electrical units of the underwater log system are actuated by water pressure obtained through the rodmeter. The rodmeter has 2 passages and extends into the water a distance of about 3 feet. Being located at the forward part of the ship, it is in relatively smooth-flowing water, since the water at this point is least affected by the movement of the ship or by the turbulence created by action of the propellers. When the ship is at rest, the water pressure is equal in both passages of the rodmeter and is due only to the weight of the water above the system. This pressure is known as static pressure. As the ship moves forward, the movement creates additional pressure in the

  forward passage of the rodmeter. This added pressure is known as dynamic pressure. The difference between these pressures is the actuating force that operates the system.

The method used to convert the dynamic pressure into indications of speed and distance differs as follows in the three underwater log systems used in service.

1. Rotary balance type underwater log system. An underwater log system of the rotary balance type employs a rotary balance unit consisting of an automatically controlled motor-driven centrifugal pump that develops a pressure to oppose the dynamic pressure from the rodmeter. The pump is connected to the dynamic passage of the rodmeter and to the inner part of a sensitive bellows assembly. The outside of the bellows assembly is connected to the static passage of the rodmeter. Pressure differences between the passages in the bellows cause it to expand or contract, thereby moving a rod which in turn actuates a motor driving a rheostat. This rheostat controls the speed of the pump motor and is known as the transtat assembly. Any increase or decrease in dynamic pressure caused by variation of the ship's speed causes a movement of the transtat arm, resulting in a change in speed of rotation of the pump drive motor. The speed of rotation of the pump motor therefore, is always proportional to the speed of the ship through the water.

 
163

Figure 12-3. Schematic diagram of underwater log system.
Figure 12-3. Schematic diagram of underwater log system.
 
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Figure 12-4. Elementary diagram showing fundamental principle of operation of underwater log system.
Figure 12-4. Elementary diagram showing fundamental principle of operation of underwater log system.
The pump motor shaft is geared to a selsyn transmitter by means of which rotary motion proportional to the speed of the ship is conveyed to 2 selsyn indicators. One of these indicators is geared to a mechanical counter in the master speed indicator which registers the total distance traveled in miles. This same selsyn indicator, through suitable gearing and in conjunction with a time element derived from the constant frequency a.c. supply, operates a pointer that shows the speed of the ship in knots. The other selsyn indicator driven by the pump motor transmitter operates a mechanical counter in the remote speed and distance instruments. Remote indications of the ship's speed are transmitted by a selsyn transmitter in the master speed indicator driven by the miles per hour pointer shaft. Speed input to fire control and navigational equipment is obtained from this same transmitter.

2. Mercury manometer type underwater log system. The mercury manometer type of underwater log system installed in some older submarines uses a mercury manometer instead

  of bellows as the means of actuating the mechanism for indicating the speed and distance traveled.

The mercury manometer consists of 2 tubes containing mercury. They are connected at the top to the dynamic side of the rodmeter. A pipe line connects the 2 manometer tubes at the bottom ends and has an opening in the center to allow mercury to enter a chamber containing a float. The static pressure is admitted into the top of this float chamber. Any change in dynamic pressure causes a change in the level of the mercury in the float chamber, thus causing the float to position itself accordingly. A rack attached to the top of the float drives a gear coupled in turn to the main shaft of the transmitter mechanism.

The transmitter mechanism is the master speed and distance indicator as well as the transmitter for remote indications. The main shaft of the transmitter mechanism is directly connected to the master speed dial. Thus, the master speed dial is positioned directly by the movement of the mercury in the float chamber

 
165

Figure 12-5. Schematic diagram of rotary balance type underwater log system.
Figure 12-5. Schematic diagram of rotary balance type underwater log system.
 
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Figure 12-6. Arrangement of units of rotary balance type underwater log system.
Figure 12-6. Arrangement of units of rotary balance type underwater log system.
 
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Figure 12-7. Pitometer log mercury manometer type units.
Figure 12-7. Pitometer log mercury manometer type units.
 
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and indicates the correct speed without any electrical connection. The speed indication is transmitted to speed repeaters in the control room and conning tower by means of selsyn units.

Distance indication is obtained from the speed element by means of a mechanical integrator using constant frequency input as a time element. It is transmitted to the control room and conning tower through selsyn units.

3. Bendix type underwater log system. The Bendix type underwater log system is actuated by the expansion and contraction of a bellows similar to the assembly used in the rotary balance type system. When a change in dynamic pressure occurs, the bellows move a diaphragm to which is attached a bellows rod. Movement of the bellows rod actuates a main balance arm that carries a contact maker. Any movement of the main balance arm and its associated contact maker closes the circuit to an actuator motor. This actuator motor in turn drives a combination cam and gear in the center of which is mounted the speed pointer.

The main balance arm is attached by a coil spring to another arm, known as the main force arm. Approximately at the midpoint of the main force arm is an extension with a cam roller on its extreme end. This cam roller at all times rides on the cam part of the cam and gear combination driven by the actuator motor. The resulting pressure of the cam on the cam roller causes the main force arm to swing in a direction opposite to the original movement of the main balance arm. This motion tends to return the main balance arm to the neutral position due to the spring tension between the two arms. At this point the actuator motor contact is broken, the motor stops, and the combination cam and gear with its attached speed pointer remains in its assumed position.

The auxiliary balance arm is connected to the main balance arm by means of a spring and swings independently of it. It is positioned by the setting of the adjustment on the guide slot and by means of the lead screw driven by the actuator motor. Tension on the auxiliary

  balance arm spring tends to aid the main force arm in returning to the NEUTRAL position. The function of this auxiliary balance arm and connecting spring is to permit setting of a calibration correction that is dependent upon the speed and to affect the neutral point at which the main balance arm settles for each speed.

The driving gear for the speed transmitter is in mesh with the gear of the cam and gear combination driven by the actuator motor. The transmitter is a conventional selsyn unit connected to speed indicators in the conning tower and control room.

Distance indication is obtained from the master speed indicator by means of a mechanical integrator using constant frequency input as a time element and is transmitted to the control room and conning tower through selsyn units.

12B2. Operation. After the rodmeter is lowered, the complete system is placed in operation by turning switches marked 1Y, 2Y, and 3Y, located on the I.C. switchboard, to the ON position. When switch lY is closed, speed indications are transmitted to the conning tower and control room. This switch also completes the circuit for the speed input to the torpedo data computer, gyrocompass, and dead reckoning indicator. Switch 2Y completes the circuit from the 115-volt a.c. bus to the selsyn transmitter for distance indications in the conning tower and control room.

Switch 3Y completes the circuit from the controlled frequency a.c. bus to the synchronous motor (time element) in the master instrument in the forward torpedo room or control room.

12B3. Maintenance. Adjustment or repairs should not be attempted without reference to the manufacturer's instruction book for specific instructions.

NOTE. Complete and detailed information on all phases of the theory, operation, and maintenance of the log may be found in Submarine Underwater Log Systems, NavPers 16168.

 
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Figure 12-8. Schematic arrangement of Bendix bellows type log.
Figure 12-8. Schematic arrangement of Bendix bellows type log.
 
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Figure 12-9. Schematic diagram of Bendix underwater log master transmitter Indicator.
Figure 12-9. Schematic diagram of Bendix underwater log master transmitter Indicator.
 
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C. PROPELLER SHAFT REVOLUTION INDICATOR
AND COUNTER SYSTEM
 
12C1. Description. a. General. The purpose of the propeller shaft revolution indicator and counter system is to transmit indications of propeller rpm and total revolutions from the propeller shafts to the control station in the maneuvering room. The system is designated as circuit K and consists essentially of the following parts:

1. Transmitters located in the motor room and geared to the propeller shafts.

2. Indicators in the maneuvering room at the control station. These indicators have a pointer to indicate rpm, a counter to indicate total shaft revolutions, and a backing signal. The system operates on a constant frequency power supply of 115-volt, 60-cycle, single-phase, alternating current obtained from the constant frequency control unit through fused switches on the I.C. switchboard.

b. Transmitters. Each of the transmitters in the motor room consists of a conventional selsyn transmitter geared to its respective propeller shaft, which transmits rpm indications to its allied indicator in the maneuvering room. In the watertight cases containing the transmitter units is a simple mechanical counter. It is chain driven by the transmitter shaft and indicates total shaft revolutions. The transmitters are designed to operate in only one direction and carry a unidirectional device that maintains a constant direction of rotation regardless of the direction of rotation of the propeller shafts.

The visual backing signal in the maneuvering room indicator is actuated by a pair of contacts located at the top of the unidirectional device. Normally, these contacts are open and no signal is indicated. When the propellers rotate in the reverse direction, the arm carrying the reversing gears in the unidirectional device closes the contacts, thereby actuating a magnet which pulls into view a white letter B in a red field signifying back rotation of the propeller shaft.

Essentially, the transmitter units of the two

  types of shaft revolution indicator and counter systems in service are the same. The indicator units, however, while employing the same principle of operation, differ considerably in construction and detail.

c. Indicator units. 1. Electric Tachometer Corporation type. The selsyn indicator (motor) (Figure 12-12) actuated by the transmitter in the motor room carries spiral gears on its shaft. These gears drive a screw shaft in a constant direction and at a speed proportional to the speed of the propeller shaft. Threaded on the screw shaft is a nut to which is attached a friction wheel. The rim of this friction wheel is always in contact with a friction disk below it. The friction disk, driven at a constant speed of 96 rpm by a synchronous motor, is pressed against the edge of the friction wheel by a spring. Thus, when the friction wheel is in the center of the friction disk, it is held stationary, but, as it is moved outward by the rotation of the screw shaft in the nut, it begins to rotate. The speed at which it rotates is dependent upon its position on the face of the friction disk. As long as this speed is less than the speed of the screw shaft, the wheel and nut continue to move outward until the wheel reaches a spot on the friction disk where its speed is equal to the speed of the screw shaft. At this point there is no longer any tendency for the nut and friction wheel to move along the screw shaft, and the wheel rides on a circle of radius exactly proportional to the propeller shaft speed.

The rotating nut carries with it, on ball bearings, a rack sleeve that is restrained from turning. Along the side of this sleeve is a rack gear meshing with a small pinion on the shaft carrying the pointer. The pointer comes to rest at a position determined by the finally balanced position of the friction wheel, and thus indicates on a properly divided scale, the rpm of the propeller shaft.

The indicator unit also contains a mechanical revolution counter. The counter is gear-driven off the end of the screw shaft and indicates total shaft revolutions.

 
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Figure 12-10. Schematic diagram of propeller shaft revolution Indicator and counter system.
Figure 12-10. Schematic diagram of propeller shaft revolution Indicator and counter system.
 
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Figure 12-11. Pitometer log type of shaft revolution transmitter.
Figure 12-11. Pitometer log type of shaft revolution transmitter.
 
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Figure 12-12. Schematic arrangement of Electric Tachometer Corporation type indicator and counter system.
Figure 12-12. Schematic arrangement of Electric Tachometer Corporation type indicator and counter system.
Figure 12-13. Top view of propeller shaft revolution
transmitter, Electric Tachometer Corporation type
with cover removed.
Figure 12-13. Top view of propeller shaft revolution transmitter, Electric Tachometer Corporation type with cover removed.
  2. Pitometer log type. The Pitometer log type indicator (Figure 12-15) operates on the same principle as the Electric Tachometer type. The essential difference in construction is that the indicator shaft drives one half of a differential gear assembly and the friction disk drives the other half. The screw shaft is rotated by a separate reversible motor and moves the friction wheel across the face of the friction disk in a manner similar to that of the Electric Tachometer instrument. The friction disk is driven by a constant speed synchronous motor at a speed of 100 rpm. The screw shaft driving motor is started, stopped, or reversed by a set of contacts mounted on the shaft that carries the pinion gear of the differential assembly. When the indicator motor begins to rotate its half of the differential, a movement of the pinion gear results because the other half of the differential is stopped, or is rotating very slowly. Movement of the pinion gear closes the contacts for the screw shaft driving motor, causing the friction wheel assembly driving the other half of the
 
175

Figure 12-14 Schematic arrangement of shaft revolution transmitter.
Figure 12-14 Schematic arrangement of shaft revolution transmitter.
 
176

differential to move outward across the friction disk. This movement of the friction wheel away from the center of the friction disk causes the wheel and its associated differential gear to rotate at a constantly increasing speed. This speed continues to increase until it is equal to the speed of the other half of the differential. When the point is reached at which there is no more turning effect imparted to the pinion gear, the contacts operated by the pinion gear shaft open and the screw shaft driving motor stops. The friction wheel assembly is then positioned on the friction disk and remains there until a change in propeller shaft speed again causes a mechanical unbalance of the differential.

The pointer shaft is directly geared to the screw shaft and gives a steady indication of propeller rpm on a properly divided scale.

The indicator motor also drives, through gearing, a mechanical counter which indicates total shaft revolutions.

  12C2. Operation. The system is placed in operation by turning switches marked 1K and 2K on the I.C. switchboard to the ON position. These switches energize the circuits to the starboard and port transmitters. Switches 8K1 and 8K2, also on the I.C. switchboard, must be turned to the ON position in order to energize the circuits from the constant frequency bus to the starboard and port synchronous motors which drive the friction disks.

NOTE. If the synchronous motor circuits are not energized, there will be no force to prevent the friction wheel from traveling to the extreme outer edge of the friction disk, thus causing the instrument to indicate maximum rpm regardless of the speed of the propeller shaft.

12C3. Maintenance. When the propeller shafts are stopped, the friction wheel should not

Figure 12-15. Schematic arrangement of Pitometer
log type propeller shaft revolution
indicator and counter system.
Figure 12-15. Schematic arrangement of Pitometer log type propeller shaft revolution indicator and counter system.
 
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Figure 12-16. Details and wiring diagram of Pitometer
log type master indicator.
Figure 12-16. Details and wiring diagram of Pitometer log type master indicator.
be in such a position as to indicate zero rpm. It should indicate between 2 and 4 rpm. In order to indicate zero, the friction wheel would have to come to rest at the exact center of the friction disk, and the revolution of the disk would impart a twisting motion to the rim of the friction wheel. The resulting friction would grind a flat spot on the rim of the wheel and a depression in the center of the disk.

No adjustments, lubrication, or repair should be attempted without reference to the detailed instructions contained in the manufacturer's instruction book.

12C4. Propeller revolution indicator system, magneto type. Late design submarines employ a very simple revolution indicator system based on the magneto voltmeter principle (see Figures 12-18 and 12-19). Geared to each propeller shaft is a small, enclosed, permanent magnet magneto of the 2-wire d.c. type which transmits a direct current proportional to the

  Figure 12-17. Shaft revolution indicator, Electric
Tachometer Corporation type, with face removed.
Figure 12-17. Shaft revolution indicator, Electric Tachometer Corporation type, with face removed.
 
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Figure 12-18. Shaft revolution indicator, magneto type, maneuvering room indicator.
Figure 12-18. Shaft revolution indicator, magneto type, maneuvering room indicator.
Figure 12-19. Shaft revolution indicator, magneto type,
shaft transmitter, with cover removed.
Figure 12-19. Shaft revolution indicator, magneto type, shaft transmitter, with cover removed.
  rotational speed of the shaft. A mechanical counter indicating only total ahead turns is built into the same housing as the magneto. The indicator for each shaft consists of 2 voltmeters mounted in a simple housing on each side of the control cubicle, one being calibrated for and reading ahead speed, and the other reading astern speed for that shaft. The system resembles the engine tachometer system. It requires no external source of energy, and connecting it to any source of power will damage the instrument.
 
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