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CHAPTER 11

PLOTTING EQUIPMENT

Introduction
 

Information about own ship's course (Co) and own ship's speed (So) is used both in navigating (dead reckoning) and in plotting and tracking sonar targets. Own ship's speed is measured by a device called the underwater log. The term "log" originated from the earliest method of measuring ship speed. This method consisted of attaching a line with knots tied in it to a log and then dropping the log into the water. The theory behind this method was that the log would be stationary in the water, and by counting the number of knots paid out in a unit of time, the speed of the ship could be calculated. This early method left a heritage of two names-"knots" and "logs." The speed of the ship is now measured with better accuracy by the underwater log. The speed is indicated on meters in the chart room and bridge and is used in dead reckoning, plotting, and tracking of own ship's course on the plotting table. The speed must be interpreted with information about own ship's heading for dead reckoning, plotting, and tracking. The north-south (N-S) and east-west (E-W) components of own ship's motion are extracted automatically by a device called the dead-reckoning analyzer (DRA).

The DRA combines the speed information from the underwater log and the course information from the ship's gyrocompass and extracts the N-S and E-W components of the ship's travel. The information is presented on three counters calibrated in miles-one counter indicates the distance in miles traveled through the water in the N-S direction, the second indicates the distance in miles traveled through the water in the E-W direction, and the third indicates total miles traveled.

The N-S and E-W outputs of the DRA are transmitted electrically to a large plotting device called the dead-reckoning tracer (DRT). The DRT has a mechanism that positions a pencil or a light

  beam in two coordinates according to the N-S and E-W data from the DRA, and some models have dials that indicate the latitude and longitude of the ship. A complete dead-reckoning system consists of a DRA and DRT, uses information from the underwater log and ship's gyrocompass, and has a pencil plot and dial indication of ship's position and path of motion.

The dead-reckoning system and the underwater log are primarily navigation equipments. Their outputs are combined with the sonar information in the attack plotter, which is an electronic instrument used as an aid in making an antisubmarine attack. The plotter uses information from the DRA, the gyrocompass, and the sonar to make a presentation on a cathode-ray tube indicator. The indicator presents the (1) course of the ship, (2) path of each searching sound beam, (3) position of an underwater target, and (4) firing range and proper bearing for the forward-throwing depth-bomb launcher.

The discussion in this chapter begins with a brief description of log systems for measuring speed and distance. The Bendix and pitometer underwater logs are described. The dead-reckoning system is discussed next. Finally, the attack plotter is described.

PITOMETER LOG

The pitometer log manufactured by the Pitometer Corporation, is an underwater log-that is, it uses a rod projected below the keel to measure speed and distance. The type of pitometer log in present use is the rotary-balance log. An older type, the mercury manometer log is no longer used.

The rotary-balance type underwater log, shown in figure 11-1, consists of (1) the sea valve and rodmeter unit, (2) the rotary distance transmitter, (3) the control unit, and (4) indicators.

 
213

Components of the pitometer log.
Figure 11-1 -Components of the pitometer log.

 

Sea Valve and Rodmeter

The rodmeter is a flat tube, 48 inches long. It has orifices in the leading edge of the tip, and on each side of the tip. The orifice on the leading edge develops a dynamic pressure that depends on the speed of the rodmeter through the water. The other two orifices develop a static pressure that depends only on the depth of immersion. The dynamic pressure is transmitted to the rotary distance transmitter, while the static pressure is transmitted to the control unit. The dynamic pressure, which varies in .relation to the speed of the ship, is compared to the static pressure, and the differential is indicative of the speed of the ship.

The sea valve is a gate valve through which the rodmeter is projected into the water. When the ship is docking, the rodmeter is raised and the sea valve is closed.

Control Unit

The control unit contains two bellows and a balance bar. One bellows is connected hydraulically to the static nipple of the rodmeter. The other bellows is connected hydraulically to the center nipple of the pump on the rotary distance transmitter. The balance bar between the bellows has electrical contacts. The contacts, which are made whenever the pressures in the bellows are unequal, control the operation of a follow-up motor on the rotary distance transmitter.

  Rotary Distance Transmitter

The rotary distance transmitter consists of (1) pump, (2) pump-drive motor, (3) follow-up motor, (4) distance-transmitting unit, and (5) motor-driven transtat (variac). Whenever the two control-unit bellows have unequal pressures in them, a contact switch is closed in the control unit. The closing of this switch causes the follow-up motor in the transmitter to position a movable contact on a transtat assembly, which in turn controls the armature voltage of the pump-drive motor. The drive motor causes the pump to decrease the pressure of its input (the dynamic pressure) so that its output to the control unit bellows just balances the static pressure of the rodmeter. When the bellows have equal pressure, the balance bar in the control unit is in the center position, the follow-up motor is not energized, the transtat arm stops moving, and the drive motor causes the pump to maintain a fairly constant pressure. There is a slight hunting about the proper pressure.

There is no flow of water through the pump other than the very small amount required to expand and contract the bellows. The pump merely balances the pressures in the bellows.

The pump drive-motor speed depends on the dynamic pressure from the rodmeter, which in turn depends on the speed of the ship through the water.

The motor is geared also to two self-synchronous transmitters. These synchros are located in the rotary distance transmitter. One synchro is geared so that its rotor rotates at 60 revolutions per nautical mile, the other at 360 revolutions per nautical mile. The electrical output (stator windings) of the 60-revolution synchro is connected to a master speed indicator, usually located in the chart room. The output of the 360-revolution synchro is used in the DRA, which receives the distance information and combines it with heading information to extract its N-S and E-W components.

BENDIX LOG

The Bendix log, like the pitometer log, is an underwater log-that is, it uses a rodmeter extending below the keel of the ship for measuring ship

 
214

Bendix underwater log components.
Figure 11-2 -Bendix underwater log.
speed and distance traveled. The Bendix log, shown in figure 11-2, consists of a rodmeter-valve assembly and a master transmitter-indicator. Remote indicators for speed and distance can be connected to the master transmitter-indicator.

The rodmeter and sea valve are similar to those of the pitometer log. The rodmeter is raised or lowered through the sea valve, which can be closed when the rodmeter is raised. When the rodmeter is lowered and the ship is in motion, the

  dynamic orifice, or pitot orifice, facing the front of the rodmeter develops a pressure higher than that in the static orifice on the sides and bottom of the rodmeter.

The dynamic and static pressures are transmitted to the transmitter-indicator where they act on a diaphragm between two bellows.

When the static and dynamic pressures differ the diaphragm moves and closes a contact. This action causes an actuator motor to move a cam.

 
215

This cam is attached to a speed indicator. It repositions the diaphragm toward its neutral position, and moves gears which position a friction wheel on the surface of a disk. Because the disk is rotated by a constant-speed motor, the speed of rotation of the friction wheel depends on its distance from the center of the disk.

The speed of the ship is indicated by a pointer attached to the cam. As the cam turns it exerts

  a balancing force to return the diaphragm between the bellows to its center position, and thus stop the actuator motor. A mileage odometer (Veeder counter) is attached to the output of the friction disk to register total nautical miles traveled.

Speed and distance indications are transmitted by synchros to remote indicators and to the dead-reckoning system.

 
Dead-Reckoning Systems
 

FUNCTIONS

The purpose of the dead-reckoning system is to indicate on dials the ship's position in latitude and longitude, and to provide a record of own ship's position relative to a fixed starting point on a graph or dials. When properly set at the starting point, the dials indicate continuously and automatically the ship's present latitude and longitude, computed by dead reckoning. The total distance traveled by the ship, regardless of course, is indicated on a counter. In addition to total miles, the system has counters that indicate the N-S and E-W mileage. The system uses information from the underwater log and the gyrocompass to accomplish its functions.

COMPONENTS

The dead-reckoning system (figure 11-3) consists of two major units-the analyzer (DRA) and the tracer (DRT). The DRA is shown on the left in figure 11-4 and the DRT on the right.

In the DRA, the distance input, obtained from the underwater log, is combined with the course input from the gyrocompass to determine and indicate on appropriate counters the total distance traveled, as well as the components in the N-S and in the E-W directions. These distance components are then transmitted to the tracer by means of the step transmitter.

In the tracer, the signals from the step transmitter actuate motors, which in turn operate a mechanism for driving (1) the pencil carrier, to record a geographical plot of the ship's travel, and (2) the dials, to indicate the latitude and longitude. On some models, a clock mechanism is electrically connected to the pencil carrier to record elapsed time on the graphic plot.

  Analyzer

The DRA has three parts-the distance converter, the roller carriages, and the ship's course crank-arm mechanism.

The distance converter consists of the synchro receiver, G, which drives disks M1 and M2. The synchro receiver is connected to the transmitter in the underwater log, which rotates at 360 turns per nautical mile of travel. Therefore, disks M1 and M2 rotate at a speed proportional to own ship's speed. The total miles of own ship's travel is indicated directly on the Veeder-Root counter, J.

The roller carriages, P1 and P2, are movable carriages that are positioned on guide rods R1 and R2 by a crank-arm mechanism controlled by the gyro-compass. The position of the carriage on the guide rod determines the spot at which the roller, L1, bears against the drive disk, M1. Because L1 is rotated by friction drive from M1, the speed of L1, depends on its position on M1. A position at the top of M1 (figure 11-3) corresponds to due south. A position at the center corresponds to due east or due west (zero N-S component). Thus the N-S component of the ship's travel is extracted by the position of L1 on M1 and is indicated on Veeder-Root counter N1. Similarly, the E-W component of travel is extracted by disk L2,, which bears against M2, and is indicated on Veeder counter N2. The motions of L1 and L2 are transmitted to the tracer by step transmitters.

The ship's course crank-arm mechanism positions the roller carriages in accordance with information received from the gyrocompass. The synchro receiver, V, receives the gyrocompass information and moves the brush contact on the front of own-course dial X. When the brush contact touches one of the split-ring contacts, it energizes the course follow-up motor, U. The follow-up

 
216

FOLDOUT-Figure 11-3 -Dead-reckoning system.

motor moves the crank-arm mechanism to position the roller carriages. When the split rings on X are in a position such that they do not touch the brush contact the follow-up motor stops. The ship's heading is indicated directly by the own-course dial.

Tracer

The scale to which the ship's course is plotted is adjustable from 1 to 4 and from 4 to 16 miles per inch by means of handles on Z1 and Z2. Vernier dials show the scale selected. The scale can be changed to 200 yards per inch-the scale usually used in sonar-by a gear changer (not shown in figure 11-3).

Motors X1 and X2 are 6-pole step motors that receive signals from the step transmitters O1 and O2 in the analyzer. The transmitter consists of three contacts and one eccentric that closes the contacts. As the eccentric rotates it closes the contacts in

  succession and causes the step motor to follow the motion of the eccentric. The motion of the step motors is translated into motion of the tracing pencil by mechanical gearing that positions the pencil in two coordinates. Motor V1 is called the latitude motor because it positions the pencil in accordance with N-S motion. Motor V2 is called the longitude motor because it positions the pencil in accordance with E-W motion. Because 1° of latitude equals approximately 60 miles anywhere on the surface of the earth, the latitude motor, V1 is geared directly to latitude dials F1, which indicate the latitude of the ship's position. Because the number of miles corresponding to 1° of longitude varies with latitude, however, a variable-speed roller mechanism connected to the latitude motor is inserted between the longitude motor, V2 and the longitude dials, F2.
 
Attack Plotter
 
PRINCIPLES

The attack plotter (AP), shown in figure 11-4, is an electronic instrument used as an aid in making antisubmarine attacks. The instrument uses information from the DRA, the underwater-sound echo-ranging equipment, and the gyro-compass. This information is used by the attack plotter to develop on the screen of a cathode-ray tube, a plot which contains (1) the course of the ship on which the instrument is installed, (2) the path of each searching sound beam from the ship, (3) the position of the underwater target when each sound contact is made, (4) the course of the target as successive target positions appear, and (5) the firing range and proper bearing for the forward thrower so that correct train and firing time may be determined.

The attack plotter Mk 1 Mod 2 (figure 11-4), has a cathode-ray indicator and a predictor-line bearing dial on the top face. Positioning and other operating controls are on the front surface. The master control is a large 6-position rotary switch, called a type-JB switch, mounted adjacent to the attack plotter.

Figure 11-5, A, shows a ship echo ranging on a submarine. The appearance of the plot on the AP is shown in figure 11-5, B. Own ship's

  position is shown as a bright spot which appears on the screen each time the underwater-sound transmitter is keyed. Own ship's course is depicted by a succession of these bright spots. The cathode-ray screen has long persistence so that each spot fades slowly and remains visible for about 2 minutes in a reasonably dark location.

The path of each underwater-sound transmission is traced by the sound-sweep, which moves out across the screen from own ship's last position in a direction determined by the heading of the transducer. The spot leaves a faint trace marking the direction of the transmission. Each time the sound equipment is keyed the spot returns automatically to a new own ship's position. Thus, the operator must keep the attack plotter in step with the sound equipment even though the keying interval is changed.

The trace brightens and leaves a persistent spot when an echo from a target is received. The position of this echo spot shows the range and bearing of the target. A series of echo spots discloses the course and speed of the target.

The range of the target is desired-not the total distance the sound travels. The sound impulses which register an echo from a submarine at 800 yards, for example, travel 1,600 yards from the ship to the target and back. The scale

 
217

Photo of attack plotter, Mk 1 Mod 2.
Figure 11-4 -Attack plotter, Mk 1 Mod 2.
of the indicator is 250 yards to the inch. Because the speed of sound in water is approximately 4,800 feet per second, the rate of sound-spot travel on the screen is 3.2 inches per second. The plot shown in figure 11-6 can be used to advantage in (1) helping to identify the nature of the target, (2) helping the sound operator regain a lost contact and (3) conning the ship, when the plot has developed enough to indicate the target's course.

Figure 11-6 shows the plot of the attack at the time the ship is approaching firing range. The bright line pointing ahead of own ship's position is the predictor line. Its length is adjustable and can be set to equal the forward throwing range. Its bearing may be varied through 360° to determine the proper bearing for the forward thrower. The front end of this line predicts where the center of the forward-thrower pattern may be placed so that firing time and forward-thrower train can be determined. The predictor line can be varied in length from 190 to 280 yards. It can be made also 1,000 yards in length. Thus, it can be used for checking the calibration of the plot.

  A major advantage of the attack plotter is the immediate appearance on the screen of any last-minute maneuver of the submarine. The train of the forward thrower can be corrected quickly to nullify the evasive tactic.

A dial called the predictor-bearing dial is adjacent to the screen (figure 11-4) and gives the true bearing of the predictor line, which can be set to indicate the proper train for the forward thrower. A synchro repeater, type 1-F, can be used to indicate this bearing at a remote point.

The attack plotter brings together information from the DRA, the gyrocompass, and the sound gear. The plot develops immediately with each ping and echo, and the accuracy of the information may be evaluated continually. Skill is required on the part of the operator to interpret the plot to best advantage.

OPERATION

Figure 11-7 is a simplified block diagram of the attack plotter.

It is desired to have the indicator spot represent own ship's position. This representation is

 
218

Appearance of plot compared with actual conditions.
Figure 11-5 -Appearance of plot compared with actual conditions.
accomplished by using the N-S component of own ship's motion to energize the vertical-deflection coil of the indicator, thus positioning the spot vertically on the indicator. Similarly, the E-W

Later stage of typical attack as firing range is
approached.
Figure 11-6 -Later stage of typical attack as firing range is approached.

  component of own ship's motion is used to energize the horizontal-deflection coil of the indicator and thus position the spot laterally on the indicator.

The sound sweep is developed by adding sweep signals in series with own ship's position signals. For example, if the transducer is pointed due north, a sweep signal is applied only to the vertical-deflection coil. This signal is applied in series with the N-S component of own ship's signal, which is continually applied to the vertical-deflection coil. Thus the spot is swept vertically on the indicator, and begins its sweep at own ship's position.

The plot is developed by having the vertical sweep of the indicator represent the N-S components of both the sound-beam motion and own ship's motion. Similarly, the horizontal sweep represents the E-W components of the sound-beam and own ship's motion. Own ship's motion must be added to the sound-beam sweep because the speed of sound in water is slow and there is motion of the ship between successive pings.

The simplified block diagram in figure 11-7, illustrates the principles of operation of the attack plotter. It shows that the N-S and E-W components of the sound sweep are obtained from a

 
219

Simplified block diagram of the attack plotter.
Figure 11-7 -Simplified block diagram of the attack plotter.
 
separator and then applied to the vertical- and horizontal-deflection amplifiers. It shows also that the N-S and E-W components of own ship's motion are received from the DRA and are applied to the deflection coils.

The spot is deflected on the indicator by three signals-(1) own ship's position, (2) the sound sweep, and (3) the predictor line. The three signals appear on the indicator, as shown in figure 11-6. Note that own ship's-spot signals are impressed on the deflection amplifiers at all times, and that the sound-sweep and predictor signals are impressed (with own ship's-spot signals) alternately by the switch.

As in conventional PPI indicators, targets are indicated by modulating the intensity of the sweeping spot. The spot is brightened also by (1) a signal from the circuit of own ship's spot, to intensify the spot that indicates own ship's position, and (2) a signal from the predictor circuit, to intensify the predictor line. The intensified own ship's spots, predictor line, and target returns are shown in figure 11-6.

  Own Ship's Spot

Own ship's spot is an intensified spot that indicates own ship's position. Each sound sweep starts at own ship's spot. The position of the spot is determined by the N-S and E-W components of ship's motion as received from the step transmitters in the DRA. These two signals are applied to the vertical- and horizontal-deflection coils to move own ship's spot on the face of the indicator. The operator can locate own ship's spot anywhere on the face of the indicator by rotating the E-W and N-S positioning controls.

The complete block diagram and the circuit schematic are shown in figures 11-8 and 11-9 respectively.

The E-W and N-S components of own ship's travel are received from the step transmitters in the DRA (figure 11-3). These signals cause the step motors in the attack plotter to follow the motion of the eccentric in the step transmitters. Step transmitters and motors were described briefly in the explanation of the DRA and DRT.

 
220

FOLDOUT-Figure 11-8 -Complete block diagram of the attack plotter.

The position of the spot on the indicator is determined by the grid bias on the deflection amplifiers V503 and V504 in figure 11-9. The bias is controlled by the ring-potentiometers R142 and R143, which determine the charge on capacitor s C503 and C509. The ring potentiometers are simply voltage dividers that determine the charge on the capacitors and thus the bias of the deflection amplifiers. The position of the movable contact of the ring potentiometers is controlled by hand or by step motors through a slip clutch. The hand controls are used to position the spot on the face of the indicator. The step motors cause the spot to follow own ship's motion.

Sound Sweep

The sound sweep is the trace that indicates the path of the searching sound beam. The sweep starts at own ship's spot each time the transducer is energized. It is shown in true bearing by taking the output of a synchro transmitter (used as a control transformer) geared to the transducer and energized by the gyrocompass. The N-S and E-W components of the true sound bearing are extracted in T501 and T502.

The input to these transformers comes from the three rotor leads of the control transformer. The rotor of the control transformer is connected mechanically to the sound head, and the three stator leads are connected electrically to the ship's gyrocompass.

The purpose of transformers T501 and T502 is to split the angular input voltages into two rectangular components of direction-one to the N-S sweep unit, and one to the E-W sweep unit, as shown in figure 11-7.

The voltage fed to the N-S sweep unit no longer contains complete sound bearing sense. It contains a voltage which is proportional only to the N-S bearing. Similarly, the voltage fed to the E-W block contains a voltage proportional only to the E-W bearing.

In the case of the N-S branch, the voltage is highest when the sound projector is directed exactly north or exactly south, and zero when it is directed exactly east or exactly west. Between these limits the variation is sinusoidal.

In the case of the E-W branch, the voltage is highest when the sound projector is directed

239276°-53-15

  exactly east or exactly west and zero when it is exactly north or exactly south.

Although the voltage is highest in both the north and south positions of the projector (in the N-S circuits), the two conditions are different. In one direction the voltage is in-phase with the reference voltage whereas in the other direction it is shifted 180° out-of-phase.

Both the reference voltage and N-S bearing voltage are fed into the N-S block, where the N-S sweep voltage is developed. This block represents a rectifier and filter circuits connected to give a "discriminator" circuit. The only purpose of this circuit is to combine the reference and bearing voltages, both of which are a-c, and to deliver a d-c voltage which bears the essential characteristics.

The output of the discriminator circuit varies in much the same way as the a-c input to it; that is, when maximum in-phase a-c voltage is fed in, maximum d-c positive voltage is developed. When zero a-c voltage is fed in; zero d-c voltage is developed. When maximum out-of-phase a-c voltage is fed in, maximum d-c negative voltage is developed. Between the maxima, the variation in the d-c output voltage is sinusoidal because the a-c input is sinusoidal between these points. Note that the change of phase of the a-c input results in change in polarity of the d-c output.

In the case of the N-S circuit, positive d-c voltage is developed if the sound projector is north of east or west. Negative d-c voltage is developed if the projector is south of east or west.

Thus, the N-S and E-W block may be considered to be nothing more than power supplies, the output voltage and polarity of which are governed by the true bearing of the sound projector. The vector sum of the two output voltages (N-S and E-W) is always a constant quantity because the input to both, before splitting, is derived from the same control transformer.

The two channels may not be perfectly balanced in practice because of nonuniformity of the component parts. For this reason a separate adjustment is provided for each channel. These adjustments are accomplished by sweep length adjusters and are identified by the numbers "6" and "7" in the block diagram, figure 11-8 and by resistors R504 and R514 in figure 11-9.

The rectified signal from the discriminator charges capacitors C511 and C505 through various

 
221

resistors to develop the E-W and N-S deflection signals. The sweep rate is determined primarily by the rate of charge of capacitors C511 (for E-W deflection) and C505 (for N-S deflection). The constants are fixed to produce a sound sweep of 3.2 inches per second, corresponding to a scale of 250 yards of range per inch deflection.

The sweep outputs of the phase-sensitive discriminator are negative or positive voltages that are added to the potentials of capacitors C509 and C503-the own ship's spot capacitors. As was shown previously, the potential across C509 and C503 determines the position of own ship's spot. By adding the sweep signals to the own ship's signals, the sound sweep is made to start at the own ship's spot each time the transducer is energized. Note that the return side of sweep capacitors C505 and C511 is connected to own ship's spot capacitors C509 and C503. Thus, the deflection amplifiers receive sweep and own ship's spot signals simultaneously.

The transformer, T503, connected to the cathode s of phase rectifiers V501 and V502 has an output signal which is used to intensify the predictor line, as will be described later.

Predictor

The predictor line is a virtual "yardstick" which may be placed on the viewing screen in the form of a streak of light. This line may be directed toward any point of the compass, may be adjusted to any one of a number of standard lengths, and may be turned on and off at will.

Unlike the sound sweep, and course plot, the predictor is independent of associated equipments or operations aboard own ship. It is, however, a measuring device which enables the operator to recommend a course or some definite bearing for training forward-thrown weapons.

The predictor positioning voltages are developed in a manner similar to that of the sound sweep, previously described, except that the predictor voltages are a-c instead of d-c such as those used in the sound sweep circuits. The use of a-c voltages in the predictor permits the use of simple RC circuits instead of the more complex rectifiers and discriminators used in the d-c circuits.

A differential type of synchro unit (35 in figure 11-8) is supplied with true-bearing voltage from the gyrocompass and delivers true-bearing voltage to the N-S and E-W separator.

  The differential synchro is at the panel of the attack plotter itself and is rotated by means of a control knob. The predictor unit is constructed with a detent at relative bearing 000°, and may be turned smoothly through an angle of 20° each side of this bearing, or ship's heading. This arc represents the possible training of the forward-thrown weapons. Beyond this 20° point, the control chatters with a characteristic ratchet action as it is turned, but operates normally otherwise. The chatter is an indication that the predictor line is trained beyond the limits of the weapons.

The three voltages developed by the predictor control synchro (35 in figure 11-8) are coupled directly into the separator. Here, the N-S and E-W components are separated by a resistance network. The output of the separator consists of two separate a-c voltages the magnitudes and phasing of which depend on predictor bearing.

The voltages directed into the N-S and E-W blocks vary with predictor true bearing. At due north the N-S block receives maximum in-phase voltage while the E-W block has zero input. At due south the N-S block receives maximum out-of-phase voltage while the E-W block still has zero input.

At true bearings due east and due west, the N-S block has zero input and the E-W block has maximum input-in phase in one case and out of phase in the other.

The terms "in phase" and "out of phase" are used to express a relation of the a-c predictor deflection voltage to the synchro power line. Because the signals to the scope are a-c the sweep starts at the position of own ship's spot, and, in the case of a due-north signal, is swept in a N-S direction at a rate dependent on the line frequency. The phase of the incoming signal determines which half of sweep is brightened by the voltage from the synchro powerline. In the case of a due-north signal, only the, northern half of the signal is brightened.

If the predictor bearing is changed to the due-south position, the phase relationships of the predictor voltage and the brightening voltage are reversed by 180°, resulting in the brightening of the opposite, or southern, half of the sweep.

In short, the relative amplitudes of the input signals determine which direction the sweep travels from own ship's spot; the phase relation of these

 
222

FOLDOUT-Figure 11-9 -Circuit schematic of the attack plotter.

input signals and the brightening voltage determine which half of the sweep is presented on the screen.

Echo Channel

The brilliance of the sound sweep is kept low so that it is just perceptible. The echo from the underwater sound gear is amplified in the echo amplifier and applied to the control grid of the cathode-ray tube to brighten the sweep at the instant an echo is received.

The first amplifier stage, V301 (figure 11-9), is disabled for a short interval after each ping is transmitted so that reverberation noise is not received. The length of time that the echo amplifier is disabled is made equal to the time required for relays A and B to operate. When both relays are operating, as when the predictor is in use, 0.15 second is required. When only the A relay is operating 0.075 second is required.

The lock-out voltage is taken from a plate of the gas tube in the relay-control circuit. When gas-tube V304 fires, to initiate the relay action, its plate voltage is lowered by resistor R356-7. because the plate voltage for each amplifier is taken from the plate of the gas tube, the echo amplifier, V301, is disabled until capacitor C351 charges.

The echo amplifier is a variable-mu (remote cut-off) type-6SK7 pentode. When the signal input exceeds +2 ½ volts, grid current flows, the grid bias increases and reduces the gain of the stage. The result is avc action for all signals exceeding a minimum value.

The coupling capacitor C305 and shunt capacitor C304 are proportioned so that the amplifier response falls off rapidly on either side of 800 cycles per second. This narrowing of the response reduces the output noise.

Tube V302 is a cathode follower. Because the cathode potential is held at about +20 volts by bleeder current from B+, the tube is normally cut off. Thus the plate current of the cathode follower follows only the positive portions of the signal, and the tube V302 passes only the positive half-cycle of the a-c signal.

When echo-switch S111 is in the full position, the output of V302 is coupled unchanged through C308 to the grid of the cathode-ray tube. When the switch is in the short position, the signal must pass through one section of twin diode V303. The

  cathode of this section is returned to ground through a 0.05-μf capacitor. As the diode conducts, it charges the capacitor positive and biases the diode to cut-off. Thus the first part of the signal from V302 passes through the diode and then the signal falls off. This action causes the echo to be shortened, making it more distinguishable from noise and reverberation.

Blanking and Brightening

In the following time sequence, the cathode-ray spot is (1) blanked out during retrace, (2) made bright momentarily to develop own ship's spot, (3) brightened and blanked alternately to form a bright predictor line, (4) brightened slightly to form the sound sweep, and (5) brightened considerably to form the echo return. Figures 11-7, 11-8, and 11-9 show the blanking and brightening circuits.

When the trigger key fires the type-884 gas tube, V304, the voltage at the plate of V304 is depressed. This drop in potential is applied to the grid of the cathode-ray tube through R321 to blank out the spot during retrace. Retrace occurs when relay A discharges the sweep capacitors.

The own ship's spot is formed when the A relay snaps into the sweep position. When this action occurs, capacitor C360, in the cathode circuit of the cathode-ray tube, discharges through R533 and part of R383. This discharging produces a negative pulse at the cathode of the cathode-ray tube, which brightens the spot momentarily.

The voltage for brightening the predictor line is the a-c voltage obtained from a winding of T503 in the discriminator circuit. This a-c voltage is coupled to the cathode of the cathode-ray tube whenever switch S502-3 is operated by relay B. The negative peaks of the a-c voltage brighten the beam and make the predictor line visible.

When the sound sweep occurs, the sweep intensity is adjusted by hand control R140 so that the sweep is barely discernible. The echo is positive in polarity and brightens the beam when it reaches the grid of the cathode-ray tube.

Relays A and B

The separate functioning of individual circuits in the attack plotter is included in the foregoing discussion. The description which follows shows how the circuits are coordinated-that is, how the

 
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relays are timed with respect to each other and with the external equipment.

The circuits associated with timing are shown on both the complete block diagram (figure 11-8) and, more clearly, on the smaller block diagram (figure 11-10). In the following discussion all numbers of units refer to figures 11-8 and 11-10.

In the smaller block diagram, the entire echo amplifier circuit is represented by a single block into which the echo and lock-out voltages are fed. The output consists of the echo signal which is turned off periodically by the lock-out voltage.

The starting point of the cycle of operation is the closing of the sound key which delivers an electric impulse to trigger generator 38. The generator converts this impulse into a suitable, sharp, trigger which is then used to "trip" the A relay timer, 40.

The trigger generator, 38, is employed to ensure a uniform trigger for tripping timer 40-not to amplify the keying impulse as might be expected.

The timer consists of a vacuum-tube circuit and relay, so arranged that the relay is de-energized (up, on the diagram) when the circuit is in its quiescent, or at-rest state. A negative impulse fed into this circuit upsets the at-rest state and causes the relay to be pulled down (energized) immediately. The relay remains down for about 0.075 second, when the timer finally returns to its

  at-rest state. It opens then, and remains open until the next trigger appears.

When the A relay is pulled down, the sound sweep is retraced; when it opens, the sweep capacitor proceeds to charge again. These operations were described with the discussion of the sound sweep circuit. The A relay operates three contact arms two of which are used in the sound sweep circuits. Only the third contact arm, S3A, is shown in figure 11-10.

The third contact arm is used to develop a trigger for tripping the B relay timer, 42, and for impressing own ship's spot-brightening on the cathode-ray tube. A source of positive d-c voltage, 41, is connected to the lower contact point, while the arm is connected to both the B relay timer, 42, and the cathode-ray tube, through a control, 44. The control is used to adjust the brightness of own ship's spot.

Each time the A relay is pulled down, the B relay timer and the cathode-ray tube are connected to the d-c voltage source, 41. When the A relay opens, both are disconnected from this source. In order to investigate the effects produced by the opening and closing of the circuit, the nature of the voltage delivered to the two load circuits must be considered.

Both the cathode-ray tube and the B timer circuits utilize capacitive input coupling. This

Block diagram of relay and timing circuits.
Figure 11-10. -Block diagram of relay and timing circuits.
 
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fact is important because it allows the "make" and "break" of S3A to produce entirely different effects.

Because the d-c voltage source, block 41, represent s positive voltage, voltage of this polarity is applied to the load circuits when the relay contacts close. The voltage is applied to the cathode of the cathode-ray tube and, being positive, does not brighten the spot. It does act like a blanking voltage but, because the tube is already blanked by a voltage on the control grid, no net effect results.

Similarly, the voltage applied to the B relay timer when the A relay closes, is also positive. The timer can be tripped only by a negative voltage; a positive voltage produces no effect on it.

Thus, upon closing, the A relay S3A produces no visible results. Only the upper two contact arms of the A relay are in service; they discharge the sweep capacitors and cause the retrace of the spot to own ship's position. The contacts, S3A, never-the-less do perform an operation-they charge the coupling capacitors in the cathode-ray and timer circuits. These capacitors become fully charged in much less than 0.075 second so that, when the relay is ready to open, the capacitors are in the completely charged condition.

Opening S3A leaves the coupling capacitors with a full charge and they proceed to discharge immediately through return circuits of their own. This effect produces the same result as if a negative voltage were suddenly applied to the timer and to the cathode-ray tube.

The negative voltage which appears at the cathode of the cathode-ray tube produces a momentary brightening effect. This brightening causes own ship's spot to appear, because the sweep circuits have been discharged and only own ship's position voltage is applied to the deflection amplifier.

The negative voltage which appears at the B relay timer "trips" the circuit so that the B relay is energized. The timer, which is similar to the A relay timer, holds the B relay in the down position for about 0.075 second and than allows it to return to the up position.

When B relay is pulled down, predictor voltage is applied to the cathode-ray tube by means of the upper two contact arms (not shown in figure 11-10). The lower contact arm, S3B, applies

  predictor brightening voltage to the cathode of the cathode-ray tube.

During the time that the A and B relays are performing their operations, it is important that the control grid of the cathode-ray tube not be allowed to affect the brightness of the spot. Any sounds which might be picked up by the receiver during this time would interfere with the presentation of own ship's spot and the predictor line.

In order to keep the picture "clean" only own ship's spot and the predictor brightening should be allowed to affect the brightness. This requirement is fulfilled in two ways-(1) by disabling the echo amplifier, and (2) by applying a blanking voltage to the control grid of the cathode-ray tube. Own ship's spot and predictor brightening voltages are made great enough to overcome the blanking voltage at the grid.

A lock-out timer, 39, is incorporated to develop the grid-blanking and amplifier-disabling voltages. This timer, like the A relay timer, is tripped by the trigger generated in block 38 and remains in action for a definite period of time. This time is about 0.15 second when the predictor is in use-that is, when A and B relays are both in operation. The output of the timer is called lock-out voltage and is applied both to the echo amplifier and to the control grid of the cathode-ray tube.

The lock-out voltage is negative and effectively cuts off beam current in the cathode-ray tube.

The lock-out timer, 39, also supplies lock-out voltage back to the trigger generator, 38. The result is a self-locking effect on the generator. Thus the generator is prevented from responding to any further impulses from the sound key until the relay cycle is completed. The need for this feature is obvious; once the cycle is started it should be allowed to be carried out to completion before another is started.

The preceding information is based on the assumption that the predictor is in use, because as explained earlier, the B relay operates only under these conditions. When the predictor is turned off, the B relay is disabled by the predictor switch, 47.

With the predictor off, the relay cycle is reduced to about 0.075 second. To compensate for this shorter relay cycle, the predictor switch makes connection with the lock-out timer, in the off

 
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position, shortening its time constant from about 0.15 to about 0.075 second. The shortening is effected by using the B relay plate voltage to speed the recovery time of the lock-out circuit after it has been fired by the trigger.

Although the predictor switch in figure 11-10 includes a total of three sections, only one section, 47, is shown. The other two sections are used for range selection and are shown in the complete block diagram, figure 11-8.

After the A and B relays have completed their complete cycle of operation, which requires about 0.2 second, they reach a quiescent state, and remain in that state until the next trigger pulse.

  In this quiescent state the electron beam is swept outward from the position of own ship's spot on the scope, in a direction corresponding to the bearing of the azimuth sonar equipment. The audio voltages from the receiver of the associated sonar are amplified in the AP and applied to the grid of the CR tube to brighten the sweep at a position proportional to the range of the target.

Thus, the AP provides the ASW officer with a running summary of the target movements. In the future, improved models of this equipment may be placed aboard ships of the Navy, but the basic principles of operation which have been described will probably be unchanged.

 
Mk 5 Plotting System
 
With the recent development of the underwater fire control systems, the Mk 5 plotting system has been designed.

This plotter automatically plots the position of own ship, two radar targets, two sonar targets, a time marker every 60 seconds in place of own ship, and the generated position of a target that is set up on the position keeper. These targets are plotted on an illuminated sheet of paper by imprinting a distinctive symbol in a position corresponding to the location of each of the objects to be plotted. The sequence of plotting, interval of plotting, and scale to be used are all variable. The symbols used are:

Own ship black dot
Sonar 1 black dot
Sonar 2 black dot
Radar 1 triangle
Radar 2 empty square
60-sec own-ship marker circle with dot in center
Generated plot empty circle

In addition to the automatic plotting, the system analyzes any one of the targets plotted, and indicates the course and speed of that target on suitable dials.

The system consists of (1) Mk 5 plotter, mounted on the bulkhead of underwater battery plotting room, (2) a Mk 63 control panel mounted at the side of the plotter, and (3) a Mk 55 or Mk 75 computer located underneath the plotter. The Mk 55 and Mk 75 computers are identical except that the Mk 75 uses miniature components,

  and is much smaller in size. They function in exactly the same manner.

The operation of the Mk 5 plotter is controlled by the Mk 63 control panel. Besides the various controlling switches for the system, the control panel provides remote indications of target courses and speeds computed by the computer which works in conjunction with the Mk 5 plotter. The computer automatically computes rectangular coordinates of the objects to be plotted from the bearing and range information that is fed to it. These rectangular coordinates, transmitted electrically to the plotter, are used to position the plotting arms of the Mk 5 on the plotting paper, corresponding to the position of the input bearing and range. The computer also transmits course and speed of the target selected.

When a correct analyzed solution is being transmitted from the computer, a correct solution light mounted adjacent to the indicator dial is lighted. The indication of the dial should be used only when this light is on.

A problem clock is provided on the control panel to indicate the elapsed time on the problem or contact and serves to correlate the various fire control stations and observers to the same time.

A counter indicates the elapsed time of the present analysis period.

A time-base selector permits selection of the period of duration of the analysis and also determines whether the analysis is automatically repeated or manually started and stopped. When the switch is set in either the 4-minute or the 12-

 
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minute position, a button marked "Analysis start and reset" must be depressed to initiate an analysis. Depressing the button illuminates the analyzing light adjacent to the speed dial of the course-and-speed indicator, showing that the machine is prepared for an analysis.

After illumination of the analyzing light, the next bearing and range of the station under analysis are stored by the analyzing elements and serve as a reference point for computing the course and speed on each subsequent observation by that station for the duration of the analysis.

When the time of the analysis period has been exceeded, the analyzing light and the solution light are extinguished, but the limit warning light remains illuminated. The analysis start-reset must then be depressed to clear the mechanisms for analyzing a new target. This equipment may be set automatically to initiate and terminate the analysis of the various speeds and courses.

In the plotter itself the sequence of plotting may be set so that any of the four targets and own ship may be plotted in the order desired. If the information from the targets is continuous, the unit may be set so that it plots each of them in a selected time interval. If the information is not being transmitted continuously, the unit may be operated so that it plots in a fixed sequence, but plots one target, then waits for information to be transmitted to determine the position of the next plot. If the position of the target is not transmitted within a preselected time interval the equipment automatically goes on to the next target.

  The equipment is provided also with a mode of operation in which the target information may be telemetered from an assisting ship. The mode can be initiated by turning the telemeter cycle switch to the input of the assisting ship. The enemy range and bearing from the assist ship (telemetered synchro information) is fed into the plotter computer as though it were a range and bearing from own ship.

When this information is used, two offset-measuring potentiometers are coupled mechanically to the positioning arms. Next the assist ship is plotted and the N-S and E-W components of the distance between own ship and assist ship are measured and stored in the potentiometers. The telemetered information from the assist ship is then presented to the plotter computer. This information is then altered by the stored information in the offset potentiometers, and the target is plotted in its true geographic position. After the enemy position has been plotted the potentiometers return to zero and are ready to repeat the cycle.

Enemy course and speed can be analyzed from the telemetered information and presented just as though the observations were made from own ship.

Another feature of the equipment is that the scale of the area around any of the targets or own ship can be expanded in any desired ratio to provide more accurate information.

The Mk 5 plotter provides the ASW officer with a complete running summary of the situation, permitting him to make accurate decisions quickly in conning his ship.

 
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