MPA Logo, San Francisco Maritime National Park Association, USS Pampanito, Historic Ships at Hyde Street Pier, Education Programs Maritime Park Association Home Page Maritime Park Association Home Page Events Maritime Park Association Home Page Maritime Park Association Home Page Maritime Park Association Home Page Volunteer Membership Donate Maritime Park Association Home Page USS Pampanito Submarine Historic Ships at Hyde Street Pier Education Programs About Maritime Park Association Home Page Directions to Maritime Jobs at Maritime Facility Rental at Maritime Trustees of the Association Calendar Press Room Store Maritime Map
CHAPTER 12

SOUND-RANGE AND DEPTH RECORDERS

Tactical Range Recorder
 

The tactical sound-range recorder is a dual-purpose device, designed (1) to print electrically a graphic chart of the impulses that are received from an echo-ranging sonar equipment, and (2) to determine from such a chart the proper time for firing the underwater ordnance. (See figure 12-1.) The echoes are recorded so that the slant range of a submerged object upon which the transducer is trained may be read directly from the chart. To achieve this function, the recorder must key the sonar transmitter.

The recorder has the following basic features:

1. A strip of electrochemically sensitive paper that moves at a constant speed from top to bottom of a rectangular viewing window on the front or top of the recorder.

2. A mechanism that causes a reciprocating carriage to traverse periodically and at constant linear speed across the chart in a left-to-right direction, perpendicular to the motion of the chart.

3. A contact member, fixed to the reciprocating carriage, for closing a circuit so as to cause momentary energizing of the sonar transmitter shortly after the carriage begins its constant-speed traverse.

4. A stylus, attached to the reciprocating carriage, for electrochemically marking the chart when sound is being transmitted or received.

5. A speed-changing device (gear changer) that provides two chart and two stylus speeds and therefore two maximum range scales.

Details of the range recorder vary for different models. In general, however, the basic principles are as explained in this chapter.

 
CHART DRIVE

A supply roll of moist, sensitized paper is contained in a vapor-tight tank to minimize evaporation and is withdrawn from the tank between a sponge-rubber gasket and a stainless-steel roller. The chart is gripped at the rear of the paper drive by two feed rollers, which draw it across the top of the tank unit. The feed rollers are coupled by means of a positive-drive spring clutch through a suitable gear box to a synchronous motor, thus providing constant linear speed of chart motion. A third roller, which collects the used paper record, is geared to the feed rollers through a friction clutch.

Guide bars for the reciprocating carriage are mounted at the supply end of the chart drive. (See figure 12-2.) This carriage is drawn from the left to the right of the instrument by a cord that is wound on a pulley. The pulley is rotated by a magnetic clutch, which is driven by the synchronous motor that actuates the chart drive. During its travel the carriage compresses two light helical springs, which, when the magnetic clutch is de-energized, restore the carriage rapidly to its starting point at the left of the recording paper.

MAGNETIC CLUTCH CONTROL

The current through the magnetic clutch is controlled through a gas tetrode. (See figure 12-3.) A conventional vacuum-tube rectifier supplies a d-c voltage, the positive side of which is connected to one terminal of the clutch. A 2,000-ohm resistor from the cathode of the gas tetrode completes the circuit to the negative side of the line or ground. When the gas tube is conducting, the current

 
228

Photo of tactical range recorder.
Figure 12-1 -Tactical range recorder.
through it also actuates the magnetic clutch. A small capacitor, 0101, connected to the cathode of the tube is grounded through a 1-megohm resistance. The control grid of the tetrode is connected through a 5-megohm resistance to the capacitor side of this grounding resistor. While current is flowing through the tube, the grid assumes the potential of the electric field at the grid, which is approximately 100 volts positive.

Current flows through the high-resistance combination, and a potential of approximately 80

  volts develops across the small capacitor with the polarity indicated. If, by some device the tube is deionized, the cathode drops to ground potential and the high-resistance side of the capacitor is therefore at a potential that is well below ground. The net result is that a large negative bias is applied to the control grid and the tube does not fire when anode voltage is reapplied until the capacitor discharges through the 1-megohm grounding resistor. Figure 12-4 shows the magnet box with cover and pulley removed.
 
229

Top view of the internal mechanism of a tactical range recorder.
Figure 12-2 -Top view of the internal mechanism of a tactical range recorder.
 
FLY-BACK CONTACTS

Attached to the stylus carriage is a contact member that serves a dual purpose-(1) to key the transmitter shortly after the carriage starts its motion from left to right and (2) to arrest the carriage motion by wiping across the fly-back contacts. At the right of the transmitting contact assembly is a fly-back con tact assembly (figure 12-2), the position of which may be varied from left to right by an external control.

In the course of its travel, after keying the transmitter, the stylus carriage contact establishes a circuit through the fly-back contacts, which are connected to the cathode of the gas tube and the

  positive d-c supply voltage. The stylus carriage contact, therefore, short-circuits the gas tube and magnetic-clutch combination, thereby de-energizing the clutch and deionizing the gas tube (figure 12-3). This action releases the cord pulley so that the carriage is restored to the left by the return springs. The moment the stylus carriage contact disconnects the cathode from the positive line, the cathode drops to ground potential and the control grid swings negative. The clutch therefore remains de-energized until the potential on the capacitor is reduced to the point at which the tube fires. When the tube fires, the clutch is re-energized, thereby starting the carriage again on its left-to-right excursion. This adjustable contact
 
230

Schematic diagram of the tactical range recorder.
Figure 12-3 -Schematic diagram of the tactical range recorder.
 
structure serves as a means of arresting carriage motion at any desired point in its course across the chart and is therefore called the fly-back contact.

An important result of this method of interrupting carriage motion is that the rate of keying is not strictly synchronous. The duration of time between (1) interruption of the stylus carriage motion, as caused by the fly-back contact, and (2) starting of the new pulse, is a function of the rate of decay of the charge on the grid capacitor and of the system voltage. This time delay is not necessarily a constant. Furthermore, the length of time during which the carriage moves from left to right is rigidly a function of the position of the fly-back contact. The rate of keying may, therefore, be increased by moving the fly-back contact to the left and be decreased by moving it to the right. The maximum range that may be observed on the chart is of course the maximum possible travel of the stylus.

 

STYLUS ACTION

Attached to the top of the carriage is a stylus bearing upon the chart directly above the roller over which the chart issues from the tank. (See figure 12-5.) The driving pulley cord is affixed to the carriage so that the pressure of the stylus on the paper is increased on its left-to-right, or recording, motion. The guide bars on which the stylus carriage slides are insulated from the tank structure and are connected to the output of the signal control circuit, which is actuated ultimately by the receiver. The other side of the signal circuit is connected to ground, so that an audio signal produces a current which passes from the stylus through the paper to the tank cover roller, or ground. When the current passes through the chemical, the chemical becomes a permanent dye at the point directly under the stylus. The record, then, is a series of dark traces on the chart opposite a scale, which indicates the distance to

 
231

Magnet box with cover and pulley removed.
Figure 12-4 -Magnet box with cover and pulley removed.
the object that returned the echo. The chart is calibrated directly in yards. Reverberation and random noise are correspondingly recorded, and echo identification is facilitated by repetition of a trace at a particular range. This visible "memory" of the output of the receiver amplifier is one of the most useful features of the instrument.

SIGNAL AMPLIFIER CIRCUIT

Successful operation of the recorder by very weak signals from the receiver is made possible by a 2-stage signal amplifier (figure 12-3). The input signal from the receiver is applied through a sensitivity control potentiometer, R110, to one

  grid of V103. The associated plate is resistance-coupled to the second grid of V103 which acts as a cathode follower to supply the stylus signal.

An automatic signal biasing feature is incorporated in the cathode-follower stage. This feature suppresses most of the reverberation and background impulses that lack the "solid" character of a true signal. Directly in series with the cathode is a 24-μf electrolytic condenser, C106, shunted by a 30,000-ohm resistor, R112. This combination is in series with the stylus which is shunted to ground by an additional 30,000-ohm resistor, R113. The R112-C106 combination can be shunted out by a bias switch, S103, when the

 
232

Tactical range recorder with cover open.
Figure 12-5 -Tactical range recorder with cover open.
biasing feature is not desired. The consequence of the biasing arrangement is that an amplified signal applied to the second triode causes the potential of the cathode to rise as current flows through the stylus. The charge developed on the capacitor prevents further current flow unless the cathode potential exceeds the charge remaining on the condenser, depending on the time constant of the RC combination.

The sensitivity control must be operated at minimum gain to prevent overloading of the automatic bias circuit and loss of discrimination. Under some operating conditions the biasing feature must be cut out to get the highest sensitivity.

The resistor, R113, provides a sharp cut-off for the marking sensitivity of the paper, which has a nonlinear resistance. The paper has a low resistance for strong currents but a high resistance for weak currents. With R113, the total variation in resistance is less and the signal more uniform.

  Without R113, faint signals would produce a very weak trace.

SPEED-CHANGING MECHANISM

The gear box between the synchronous motor and the feed rollers and magnetic clutch is provided with a gear shift that changes the speed of the chart in the same ratio as the speed of the stylus. (See figure 12-6.) The maximum range of the recorder is either 3,750 yards at the slow rate of stylus travel or 1,500 yards at the fast rate. This gear shift is actuated by a lever on the outside of the case of the instrument and is provided with a neutral position in which the drive is disengaged. This neutral position is of great importance in providing a standby position for keeping the recorder available for immediate use without wasting paper. If the instrument is turned off it is necessary to wait approximately 15 seconds before the rectifier circuit becomes operative.

 
233

Orientation of motor gearing.
Figure 12-6 -Orientation of motor gearing.
 
ANALYZER MECHANISM

The analyzer mechanism, which provides the second of the two functions of the recorder, is mounted as a unit on the cover casting. Its essential component is a transparent plotter bar pivoted on a casting which may be moved horizontally by a knurled knob. This casting is mounted on another casting which may be moved vertically by a crank. (See figure 12-7.) In addition, the assembly of the plotter bar and the

  horizontal casting may be moved horizontally by the firing gear knob in five steps. Affixed to this horizontal casting is a pointer, which is shifted by the cranks with respect to data scales mounted on the cover of the recorder. The position of the pointer with respect to the horizontal slide, and hence to the plotter bar, may be varied by moving the pointer in accordance with (1) the transducer-to-stern distance and (2) a selected value of firing lag, or dead time. These latter
 
234

Front view of the tactical range recorder.
Figure 12-7 -Front view of the tactical range recorder.
adjustments are semipermanent and are not altered in the course of an attack.

Another important feature of this plotter is the two data scales on the cover of the recorder. (See figure 12-8.) One, which is labeled stern introduces the proper correction for sinking time and ship's own speed for a stern barrage if the pointer is positioned with respect to the applicable data on this scale. A similar scale, labeled bow, is employed in an identical manner for introducing the proper corrections in an attack with forward-thrown weapons.

RANGE-RATE PLOT

The horizontal motion of the stylus is uniform and is scaled at one-half the velocity of sound so that its excursion rate across the chart represents 800 yards per second. As the vertical motion of

  the chart paper is geared at a fixed ratio with respect to the stylus motion, the echoes that appear on the chart form a range-rate plot. When the range rate is zero the echoes form a vertical line on the chart. When, however, the range is closing, each successive echo is on the left of the preceding one so that the leading edge of the echoes form a sloping line. The slope of this line can be translated directly into range rate in knots. This translation is accomplished by a. plotter bar, which is mounted on the analyzer mechanism and pivoted at the zero point of the range scale. When the plotter bar is pivoted so that its slope is parallel to the slope of the echoes, the range rate can be read from a semicircular scale graduated in knots. This scale is located at the top of the plotter bar (figure 12-9).
 
235

Detail of correction scales.
Figure 12-8. -Detail of correction scales.
 
BARRAGE TIMING

The combination of the analyzer and plotter bar is designed to give the correct time to release the ordnance. After the necessary adjustments for ship's speed and setting of the depth charges is made with the horizontal slide in the center, or No. 3 firing position, the slide is translated to the No. 1 firing position on the right by means of the firing knob. When the line of echo traces is observed-by the motion of the chart-to reach the center of the plotter bar, the order is given to fire the first charge. The knob is immediately turned to the No. 2 firing position, and when the traces again reach the center of the plotter bar the second charge is fired. This procedure is repeated until all the charges of the barrage are released.

  In an attack with forward-thrown weapons the procedure is almost identical, the basic difference being that the firing knob is not involved because there is no spacing to the barrage. In short, the analyzer is left with the safety on and with the firing knob in the No. 3 position. When the echo traces reach the center of the plotter bar the order is given to fire.

Because the sound information available to the recorder is always several seconds behind the actual tactical situation, a shift in doppler may indicate the recorder solution is inaccurate for firing. Thus, the conning officer may fire sooner or later than the recorder indicates. For this reason the recorder's solution of time to fire is called will to fire. The correct solution of the problem of will to fire, as provided by this analyzer, may be ascertained by a proper consideration of

 
236

Plotter-bar index at infinity on the range-rate scale.
Figure 12-9 -Plotter-bar index at infinity on the range-rate scale.
the following facts: Displacement along the direction of the chart motion may be represented as time; displacement across the chart may be represented as range. Therefore the slope of any lines with respect to these axes may be represented as rate of change of speed. This correct solution   is obtained only if the mechanism is set up with the firing knob in the No. 3 position and with the recorder running at high speed (1,500-yard scale). A safety lever normally keeps the instruments in the No. 3 position and reduces to a minimum the the chance for operator error.
 
Sound-Range Recorder
 
A range recorder that has as its only function the determination of range is commonly called a sound-range recorder instead of a tactical-range recorder. Such an instrument is incorporated in the OKA-1 sonar resolving equipment, previously described. The keying and recording actions and maximum range scales are the same as those of the tactical recorder just discussed. The sound-range recorder is housed in the top of the OKA-1 console as shown in figure 12-10. The differences between this recorder and the conventional tactical recorder are shown by the following features of the sound-range recorder:

1. Determination of sound range is

239276°-53-16

  accomplished by positioning an image of an optical cursor that is projected on the recorder chart. This optical cursor is actually driven by a synchro system, positioned externally by the operator. In addition to controlling the cursor, this synchro system transmits sound range, Rq, to the various computing circuits of the OKA-1.

2. Another control is provided to adjust the cursor's angular rotation so that the slope of the cursor image can be set parallel to the slope of the incoming signal, which is by definition, range rate, dRq. The angular position of the cursor is used to drive a rate servo system which furnishes an a-c voltage proportional to range rate, dRq.

 
237

Top view of the OKA-1 slant-range recorder with cover open.
Figure 12-10 -Top view of the OKA-1 slant-range recorder with cover open.
This range rate is transmitted to the depression-angle aided-tracking circuits.

3. The stylus drive motor of this recorder is

  provided with a variable-speed motor to allow adjustments to be made for the variation of the speed of sound at different water temperatures.
 
Depth-Determining Recorder
 
The QDA depth-determining equipment present s its solution on a chemical recorder that is similar in principle-and to some extent in construction-to the tactical-range recorder. In the depth recorder, however, the stylus travels at a speed proportional to the sine of the target depression angle-the vertical velocity of sound, Vz. The stylus can be said to move at a rate corresponding to the slope of the sound beam.

If the beam is steeply inclined the stylus moves rapidly from left to right; if the beam is nearly horizontal the stylus moves slowly. The ping is

  transmitted just as the stylus moves away from its zero position, and, at the instant the echo returns, the stylus marks the recorder paper. For a distant target the angle is small and, correspondingly, the stylus travels slowly but for a relatively long period before the echo mark is recorded. For a nearby target at the same depth, the angle is relatively large and the stylus moves rapidly for a short period before the echo mark is made.

Therefore, in both cases, the mark is recorded at the same distance from the starting position of the stylus. A linear depth scale, calibrated in

 
238

Recorder and control console.
Figure 12-11 -Recorder and control console.
feet, extends across the recorder chart. The stylus speed is controlled by the OKA-1 resolver, but the basis of this speed is determined by the QDA beam depression angle and the velocity of sound in water. A movable layer depth contact in the recorder makes possible a change in stylus speed when a thermocline is reached.   A vertical cursor light can be moved across the depth scale and aligned with the echo trace. Geared to the cursor-light lead-screw is a synchro generator which transmits the target depth information.

Figure 12-11 shows the recorder and control console.

 
239

 
Echo-Sounding Recorder
 
The recorders used with echo-sounding equipment differ from those just discussed. Because echo sounding is used in survey operations its record should be permanent. Therefore, the paper used for the record chart is of the dry type. It is impregnated with conductive materials and is coated with lead thiosulfate, which turns black upon the passage of electricity. The paper is calibrated in fathoms.

Instead of one stylus on a reciprocating carriage there are two styluses, diametrically opposite each other, on an arm that is center-driven in continuous rotation. (See figure 12-12.) When the stylus moves onto the chart the transmitter is keyed and the stylus marks the chart at the zero position.

Later, when an echo is returned from the bottom, the chart is similarly marked at the scalar position corresponding to the water depth. When the second arm rotates onto the chart another transmission-echo cycle occurs. As the chart is in constant motion and the transmissions are close together the picture on the chart is an elevation plan of the ocean floor.

Echo-sounding equipments have two ranges- shoal and deep. As it is essential to know later which scale was being used, a third stylus prints a

  line on the edge of the chart when the equipment is operated in the deep position.

Stylus arm and chart plate.
Figure 12-12 -Stylus arm and chart plate.

 
240

Previous Chapter
Previous Chapter
Sonar Home Page
Sonar Home Page
Next Chapter
Next Chapter

 

Copyright © 2013, Maritime Park Association.
All Rights Reserved.
Legal Notices and Privacy Policy
Version 3.00