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CHAPTER 15

ECHO-SOUNDING EQUIPMENT

The Echo-Sounding Problem
 

GENERAL

Determining the depth of water to ensure safe navigation is an old problem. The Bible mentions sounding in Chapter 27 of the Acts of the Apostles. The passage concerns the shipwreck of St. Paul, as follows:

"After midnight the shipmen deemed that they drew near to some country. And sounded, and found twenty fathoms; and when they had gone a little further, they sounded again, and found it fifteen fathoms. Then fearing lest they should have fallen upon rocks, they cast four anchors out of the stern, and wished for the day."

It is interesting that the word "sound," meaning to take depth measurement, derives from a different root than the word "sound," meaning a stimulus to hearing, and originally the two meanings of the word had nothing in common. Now, however, the use of echoes for "sounding" has established a new relation between the old meanings of the word.

Until recently the lead line was the primary means of sounding. Today, the lead line is used chiefly to obtain samples of the ocean bottom, because modern methods of sounding with echoes are more efficient. The latest engine-driven lead-sounding machine, employed in some geodetic survey operations, uses a 36-pound lead and is capable of taking a sounding of 300 fathoms in 3 minutes.

The present method of echo sounding is automatic and rapid. A sound is transmitted vertically downward, and the time that is necessary for the sound to travel to the bottom and return to the surface is recorded. Echo sounding is similar to the echo ranging described in previous chapters.

239276°-53-18

 
DEPTH-FINDER REQUIREMENTS

In general, the depth finder should be capable of the automatic recording of the depth in the shortest possible time interval. It must be independent of the ship's speed and must be effective in any depth of water. Depth finders in present use satisfy these requirements. Some of the smaller types do not have a recording unit, but they are useful for small vessels.

The first sonic depth finders used audible sound, which has several disadvantages. Ship noise, which is a maximum in the audible range, causes interference. Because the energy from the transducer cannot be concentrated into a beam, a great part of the energy is wasted. In the sonic range neither piezoelectric nor magnetostriction transducers can be used effectively, but there are no substitutes for them. Ultrasonic sound overcomes all these disadvantages.

Modern depth finders have the following five units in common (figure 15-1):

1. A transducer for the reciprocal conversion of acoustic and electromagnetic energy.

2. An electronic or electric transmitter-rectifier for driving the transducer.

3. An electronic receiver-amplifier for amplifying the weak echo energy picked up by the transducer.

4. An indicator for accurate and continuous indication of depth.

5. A recorder for making a permanent record of water depths over which the ship is passing.

DEPTH-FINDER COMPONENTS

Transducers used in naval sounding equipment are of three types-two of them are magnetostrictive, and the other is a crystal type.

 
269

Functional block diagram of a typical echo-sounding system.
Figure 15-1. -Functional block diagram of a typical echo-sounding system.

The first type, used in large equipment, is similar to that used in echo-ranging equipment (figure 15-2). It consists of a steel plate with nickel tubes mounted on it.

The second type is constructed of nickel laminations. The unit looks somewhat like a transformer (figure 15-3). A current passing through the coil of the winding sets the core into vibration.

The crystal transducers are constructed similarly to echo-ranging crystal transducers except that they are permanently positioned downward.

Transmitters are of two types. The transmitters for the magnetostriction and crystal transducers are in many respects like those used in echo-ranging equipment. They consist of an oscillator and a power amplifier. Transmitters used with laminated transducers are of the impulse type. A capacitor is discharged through the

Figure 15-2. -Exploded view of the NMC-2 transducer.
Figure 15-2. -Exploded view of the NMC-2 transducer.

  winding of the transducer, and the output is a damped sine wave.

Indicators are usually the source of the timing impulse to the transmitter. The type of indicators most commonly used consists of a circular rotating disk over a flashing neon light. The type used by the Radio Corporation of America has a hole in a steel tape, which continuously runs on pulleys across the face of the indicator. A long neon light lies behind the tape. The transmitter is keyed as the hole starts over the end of the tube, and the echo returning from the bottom causes the tube to flash. During the elapsed time the hole in the tape has traveled a distance proportional to the depth marked on a scale beside the tape. The tape contains several holes along its length, but only

Magnetostriction laminated transmitting projector
of the NJ-7 equipment.
Figure 15-3. -Magnetostriction laminated transmitting projector of the NJ-7 equipment.

one hole appears over the neon lamp at any instant. The tape indicator is usually not so satisfactory as the rotating type. On a small type of depth finder built by Bludworth Marine the depth is indicated on a meter. The most modern type used by Edo Corporation makes use of a circular sweep on a CRT. Depth is indicated by deflections of the sweep.

Depth recorders are all essentially of the same type. They record on a time-depth chart the depth as the time varies. The chart paper is generally of the conducting type with a thin wax insulating coating that is punctured by an electric spark caused by the echo.

 
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NMC-2 Sonar Sounding Equipment
 
GENERAL

The model NMC-2 sonar sounding equipment is typical of that used on large vessels. It provides a powerful oscillator that allows echoes to be received from depths greater than 2,000 fathoms. A pictorial view of the equipment is shown in figure 15-4. The NMC-2 is similar to the early type of echo-ranging equipment.

The NMC-2 equipment measures ocean depths in fathoms by projecting a signal vertically and measuring the elapsed time before the return of the echo from the ocean bottom. The interval between the emission of the signal and the return of the echo is timed (1) by rotating a disk at a known constant speed and (2) by noting the angular rotation of the disk during the interval by reference to a scale graduated to read directly in fathoms. In depths of less than 2,000 fathoms the operation of the apparatus is automatic, and soundings are obtained with a minimum of attention or adjustment of controls by the operator. A semiautomatic method supplements the automatic method in depths or more than 2,000 fathoms and extends the range beyond that obtainable by the automatic method. The semiautomatic method consists of listening for an audible echo signal in the speaker and noting the white-light position on the proper scale. The NMC-2 is equipped with a recorder that automatically records ocean depths down to 2,000 fathoms.

TRANSDUCER

The NMC-2 equipment uses a magnetostriction transducer of the type shown in figure 15-2. It is mounted near the keel of the ship with the diaphragm horizontal and in contact with the sea water. The normal frequency is 18 kc.

TRANSMITTER AND RECTIFIER

The transmitter and rectifier unit contains an electron-tube transmitter for generating the alternating voltage to be applied to the transmitting projector, two rectifiers for the high-voltage supply, and two starting relays and switches. A tuning control allows the transmitter frequency to be varied over a range of from 17 to 19 kc.

  This transmitter is similar to magnetostriction transmitters described in chapter 8. A simplified diagram of the rectifier is shown in figure 15-5. Plate potentials for the transmitter tubes are supplied by the duplex bridge rectifier in figure 15-5. This procedure allows virtually the full output voltage of T406 to be made available to the amplifier. The bridge circuit requires three separate and well-insulated filament windings since they are connected to opposite ends of the load circuit and have the full-load voltage between them.

The plate supply to the oscillators utilizes V407 and V408 with transformer T406 as a fullwave rectifier, and delivers approximately one-half of the total transformer voltage as d-c output.

INDICATOR-RECORDER-AMPLIFIER UNIT

The indicator-recorder-amplifier unit consists of a depth indicator-recorder and a receiver-amplifier with its power supply mounted in the same housing.

Indicator

The indicator portion is the principal control unit mounted on the bridge. An equipment start-stop button allows the equipment to be turned on from the bridge.

The timing disk rotates behind the two scales, and a slot in this disk is exposed in the space between the shoal scale and the deep scale. When the visual or automatic method of sounding is used, a neon lamp flashes behind the slot the instant the echo is received. The position at which the light flashes indicates the depth in fathoms. When the audible or semiautomatic method is used, an incandescent lamp shines continuously behind the slot and the operator listens for the echo. The position of the light at the instant the echo is heard gives the depth in fathoms. The position of the visual-audible switch indicates which method is in use, whereas the shoal-deep switch selects the scale readings.

In the 400- or 2,000-fathom position of the signal interval switch an echo indication is obtained at each revolution of the disk, whereas the 800- or 4,000-fathom position doubles the depth

 
271

Pictorial diagram of the NMC-2 equipment.
Figure 15-4. -Pictorial diagram of the NMC-2 equipment.
 
272

range obtainable on either scale. The middle position cuts out the automatic keying and permits the use of a manual test key in the transmitter. The speaker may be used during visual operation by setting the visual-audible switch in the middle position. The middle position also is used for recorder operation.   stylus makes a horizontal mark along the bottom of the chart. This mark shows that the deep scale is in use and that the indicated depth must be multiplied by five. Cut-out contacts ground the styluses when they are not over the chart paper. The chart warning lamp indicates the need for replacing the chart roll.
Simplified schematic diagram of the NMC-2 rectifier power supply.
Figure 15-5. -Simplified schematic diagram of the NMC-2 rectifier power supply.
Recorder

The recorder chart is of the dry type, impregnated with conductive material and coated with lead thiosulfate, which turns black upon the passage of an electric current. The stylus produces a mark at the zero line of the chart the instant of signal emission, and the returning echo causes the stylus to produce a second mark at a position corresponding to the depth of water. When the shoal-deep switch is in the deep position, a fixed

  Receiver-Amplifier

The receiver-amplifier unit amplifies the echo to a voltage that is sufficient to operate the red light, speaker, and recorder. It is mounted in the indicator unit and may be adjusted from the indicator panel. Controls include the tuning control, which permits the receiver to be adjusted over its calibrated range of from 17 to 19 kc. In addition, there are volume, bias, beat note, and sensitivity controls, and a phones jack for headset reception.

 
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Rectifier Power Unit

The power supply consists of a vacuum-tube rectifier with a filter circuit to supply the required d-c voltages and a-c filament for the receiver.

 
TRANSDUCER JUNCTION BOX

The leads from the transmitter to the transducer pass through a junction box. This junction box contains a capacity network for power-factor correction.

 
NJ-9 Sonar Sounding Equipment
 
GENERAL

The NJ-9 is an echo-sounding system for use on small craft. This equipment is more compact and is lighter than the NMC-2 equipment, which was designed primarily for ships larger than those of the PC type. All echo-sounding equipment has a transmitter, a transducer, a receiver, and an indicator. The NJ-9 includes (1) a visual indicator of the same type used by the NMC-2 and (2) a recorder for giving a permanent record. This recorder is identical to that used in the NMC-2. The primary difference between the two equipments is in the transducer. The echo-sounding transducer used in the NMC-2 equipment shown in figure 15-2 uses nickel tubes as the magnetostrictive element. The NJ-9 uses the laminated type of magnetostriction transmitting projector (figure 15-3), which is shock-excited by the transmitter and which oscillates at its own natural resonant frequency, thus giving a damped sine-wave output. This type of projector requires a special transmitter to produce a very high current pulse through its winding. The shape of the pulse is not critical and is obtained by discharging a capacitor through the transmitting projector at regular intervals determined by the keying interval.

Figure 15-6 shows the complete schematic diagram of the NJ-9 equipment. The illustration shows that the NJ-9 uses a separate projector and hydrophone.

There are three units and a motor-generator set in the NJ-9 system. Because the indicator-recorder used in the NJ-9 system is the same as that used in the NMC-2, it is not discussed further at this time. The other two units are the transmitter-rectifier and the receiver-amplifier.

TRANSMITTER-RECTIFIER UNIT

The transmitter-rectifier unit may be divided into three major electric circuits-(1) rectifier, (2) keying, and (3) discharge.

  The transmitter functions through the charging and discharging of capacitors. The discharge from one of these capacitors produces ionization within the discharge tube, which then becomes conductive and discharges the power capacitor through the transducer.

When power transformer T401 (figure 15-6) is energized with 115 volts of alternating current the rectifier circuit closes after a 30-second delay introduced by relay K401. This delay permits the cathode of rectifier V402 to come up to operating temperature. The a-c power is converted into high-voltage direct current, which immediately charges capacitor C403. The power-output capacitor, C404, also is charged by this high voltage through resistor R402, which introduces a time constant of 0.02 second. Simultaneously, capacitor C401 is charged through resistor R401 and is discharged through the primary of transformer T402 when the keying contacts of the indicator close. The discharge of current through the primary of transformer T402 is stepped up on the secondary of the transformer to a high voltage, which causes the argon discharge tube, V403, to ionize.

When ionization takes place, the gas in tube V403 offers a low-resistance path for discharging capacitor C404. Capacitor C404 is connected in series with the transmitting projector, and its discharge current must pass through the winding on this projector. Because the resistance of the total discharge path is small, a heavy current flows. This current causes the tube to flash a brilliant bluish-white light.

Immediately after discharging, capacitor C404 acts as a short circuit on the discharge tube, which deionizes because there is insufficient potential across the tube to maintain ionization. Capacitor C404 then is charged from the high-voltage supply and is discharged when the indicator-keying contacts close. This cycle of charging and discharging capacitor C404 is repeated approximately 120

 
274

FOLDOUT - Figure 15-6. -Schematic wiring diagram of the NJ-9 sounding equipment.

times per minute when the fathoms-keying contacts are operating and 720 times per minute when the feet-keying contacts are operating.

RECEIVER-AMPLIFIER

The receiver-amplifier consists of (1) two stages of amplification (V101 and V102) tuned to the frequency of the projector, (2) a detector (V103), and (3) an output stage (V104). A milliammeter, M101, at the front of the unit indicates the anode current of the output tube and thus provides a check on the operation of the unit. A bias adjustment, R109, operated by means of a screw driver, controls the detector bias and thus the minimum signal level. A power supply, including rectifier

  tube V105 and its filter system, provides d-c voltages for the anodes and a low a-c voltage for the tube heaters.

PROJECTOR AND HYDROPHONE

The projector and hydrophone are of the magnetostriction type, and each of them consists of an assembly of nickel laminations with an electric winding. The transmitting projector has a low impedance with only a few turns in the winding, whereas the receiving hydrophone is of much higher impedance and has a correspondingly greater number of turns. The frequency of the projector is controlled by its natural period, which is approximately 21.6 kc.

 
NK-7 Sonar Sounding Equipment
 
GENERAL

The NK-7 sonar sounding equipment is portable and is designed to operate from a 6-volt battery in boats in which no permanent echo-sounding installation can be made and where the depth to be recorded does not exceed 200 fathoms. The general arrangement of this equipment is shown in figure 15-7.

The NK-7 system is essentially the same as the NJ-9 system, but the NK-7 transmitter power

Pictorial diagram of the NK-7 sounding
equipment.
Figure 15-7. -Pictorial diagram of the NK-7 sounding equipment.

  output is not so great. The NK-7 has no visual depth indicator, only a recorder. The projector and hydrophone are of the same type as those used in the NJ-9 equipment. A schematic diagram of the complete NK-7 unit is shown in figure 15-8.

RECORDER

S101 is the main power switch. Because of the mechanical arrangement of the main switch, successive turnings alternately close and open the circuit. This switch also reverses the polarity for motor B101 but retains a fixed polarity for the chart lights, vibrapacks, and tube filaments. A specially designed cam attached to the chart feed roll operates switch S105, which keeps reversing the polarity of the input leads to the motor. This action prevents deterioration of the governor contacts caused by electrodeposition of metal from one contact to another. As a result the contacts wear evenly.

This polarity-reversing operation does not affect, the direction of stylus rotation, because the field and armature currents of B101 are both reversed simultaneously. The speed of motor B101 is closely controlled by the centrifugal motor governor. Contacts B101A of this governor are closed normally when the motor is stopped or is running slowly. As the motor speed increases beyond the correct value determined by the adjustment of the speed control, the contacts open because of centrifugal force. This action places resistor R101 in series with both the field and the armature of

 
275

Units of AN/UQN-1B sonar sounding set.
Figure 15-9. -Units of AN/UQN-1B sonar sounding set.
 
276

FOLDOUT - Figure 15-8. -Schematic wiring diagram of the NK-7 portable depth recorder.

the motor, thus limiting the flow of current and slowing down the motor.

As the motor continues to slow down, the contacts close; resistor R101 becomes shunted; current increases through the armature and field; and the motor speeds up. Thus, by action of these contacts, the motor attains the correct speed of 4,026 revolutions per minute. The speed-control knob permits adjustment of the motor speed by changing the spacing and tension of the governor contact mechanism. Capacitor C103 limits sparking of the governor contacts, which prevents interference with radio reception. Switch S106 is connected mechanically to the feet-fathoms lever. This switch is opened only when the lever is in the middle position. This operation cuts down the current to the motor by shunting the supply through resistor R102, and the motor slows down. This slowing action allows easy meshing of the gears when shifting from feet to fathoms.

When closed, the direct signal switch, S102, permits direct coupling between the transmitting element and the amplifier through capacitor C101. This coupling allows the emitted signal to be recorded immediately on the chart. This recorded transmitter signal is the zero mark. Motor B102 operates the blower, which provides forced ventilation for the recorder case.

Transmission of Signal

The electric power for energizing the magnetostriction transmitter is obtained from the 300-volt d-c output of vibrapack D101, which charges capacitor C104 through resistor R103 while the keying contacts, E103 and E102, are open. R103 is a current-limiting resistor inserted to prevent overloading the vibrapack. At the instant contacts E102 and E103 close, capacitor C104 discharges through the windings of the transmitter causing it to vibrate at its natural frequency of about 21 kc. This emitted signal occurs once each revolution of the stylus arm, at the point of zero marking on the chart.

Reception of Signal

In normal sounding, the echo is picked up by the receiver element and, after passing through the amplifier, is led to the stylus assembly in the form of high-frequency alternating current at about 300 volts. This voltage discharges through

  the chart and ground and thus produces the depth record. Resistor R104 limits the current through the stylus needle.

VIBRAPACKS

Power from the 6-volt storage battery is applied to vibrapacks D101 and D102, which in turn provide approximately 300 volts d-c. The output of the vibrapacks supply both the screen and plate circuits for the amplifier tubes. As mentioned previously, D101 also supplies electric power for energizing the magnetostrictive transmitting element.

These power units are complete assemblies. In vibrapack D102 a rapidly vibrating reed interrupts the 6-volt circuit through the primary of power transformer D102H and produces a pulsating direct current. A high-voltage alternating current is thus produced in the secondary. This current is rectified by a mechanical synchronous rectifier arrangement in the vibrator. Choke D102A and capacitor D102D provide a filter for the high voltage inside the vibrapack. Choke D102B and capacitor D102C prevent the ripple voltage from feeding back to the 6-volt line, thus preventing interference.

The operation of D101 is the same as that of D102. The output from both vibrapacks is filtered still further by capacitors C137 and C138.

Typical presentation on CRT indicator.
Figure 15-10. -Typical presentation on CRT indicator.

 
277

Block diagram of AN/UQN-1B.
Figure 15-11. -Block diagram of AN/UQN-1B.
The vibrating elements are enclosed in a metal tube having an internal sponge-rubber support, which reduces vibrator noise and insulates the elements from the metal case. Because the metal   tube is spun on to a special multiprong plug-in connector, the contacts are not accessible for cleaning or adjustment. If defective, the vibrapack must be replaced with a spare.
 
AN/UQN-1B Sonar Sounding Set
 
The AN/UQN-1B is one of the most modern types of sounding equipment being installed on ships today. In contrast with the old types of equipment, the AN/UQN-1B comprises only one small unit with its associated transducer. A photograph of the entire equipment is shown in figure 15-9. In spite of its small size, it gives very accurate readings, at a very wide range of depths, from about 5 feet to 6,000 fathoms.

The equipment is designed for installation on either submarines or surface vessels for the purpose of measuring and either indicating or recording water depths. Three recorder ranges are

  provided-0 to 600 feet, 0 to 600 fathoms, and 0 to 6,000 fathoms. Two indicator ranges are provided-0 to 100 feet and 0 to 100 fathoms. Means are provided for transmitting a single ping or for automatically keyed operation. The equipment operates by emitting a pulse of ultrasonic energy into the water and measuring the time required for the pulse to travel to the bottom and return.

When recording, a stylus starts across the recorder chart simultaneously with the emission of the pulse. The stylus moves at a constant velocity and marks the paper twice-once at the top of the chart when the pulse is transmitted and again

 
278

Typical AN/UQN-1B depth recording.
Figure 15-12. -Typical AN/UQN-1B depth recording.
when an echo returns. This procedure provides two points spaced in proportion to the depth of water beneath the transducer. Visual indication is provided by a circular sweep on the face of a cathode-ray tube (figure 15-10). The transmitted pulse and the returning echo radially modulate the trace. An engraved translucent shield in front of the CRT furnishes a scale. The transmitted pulse, which always occurs at zero on the scale, and the echo appear as small radial bars across a luminous circle. The uniform angular velocity of the trace provides the desired time-depth relationship.

The mode of operation is selected by use of the appropriate controls on the front panel of the equipment.

The transducer comprises an array of ammonium dihydrogen phosphate (ADP) crystals in a pressure-tight, flanged housing. It is designed for flush mounting in a standard hull ring of the bottom plating of a surface vessel or outside the pressure hull of a submarine. A tuning inductor

  is mounted inside the housing. This inductor, with the capacity of the crystals, forms a series-resonant circuit at 12 kc.

The dimensions and arrangement of the crystals and a monel backing plate produce maximum energy transfer at 12 kc.

There are no tuning controls on the equipment because all of the oscillators are crystal-controlled, and all frequencies are fixed. There are three oscillators that provide basic frequencies of 114, 130, and 142 kc. A fourth oscillator provides either a 4- or a 24-cps frequency to supply the circular sweep generator. These oscillators are shown in the block diagram in figure 15-11. From the three basic frequencies, the following resultant frequencies are obtained:

1. 12 kc (142-130 kc) for transmitter operation.
2. 118 kc (130-12 kc) for receiver i-f operation.
3. 4,000 cps (118-114 kc) for chart marking,

CRT modulation, and listening.

 
279

The transmitter delivers 800 watts of pulsed 12-kc power through a transmission line to the transducer. The transmitter is a series of transformer-coupled amplifier stages consisting of a single-ended input amplifier (V203), a push-pull driver stage (V204 and V205), and a class B, push-pull, power-output stage (V206 and V207). Transmitter input voltage is constant; keying is accomplished mechanically for recording and with a triggered gas tube for indicating by completing the cathode circuit of the drive tubes, input amplifier, and 130-kc cathode follower.   The receiver takes its input from the 12-kc transmitter pulse, and mixes it with a signal from the 130-kc oscillator, V201A, and the resulting difference signal of 118 kc is used as the i-f frequency. This 118-kc signal is amplified and mixed with a 114-kc signal to produce the 4,000-cps audio frequency.

The recorder is conventional and has three ranges. An actual recording sheet of this equipment is shown in figure 15-12. This equipment will perform well at any depths encountered.

 
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