Page 487 echo sounding 5266 



Table 15 will serve as a guide in setting the depth-selector and the starting-and-frequency 

 switches. Any combination of the two switches other than those tabulated must be scrupulously 

 avoided when the instrument is used for hydrographic surveying, because an error will be introduced 

 due to the relatively large time lag of the electromagnetic keying relay used in the sonic system. To 

 illustrate the use of table 15, if the depth of water, in fathoms, is between 3 and 20, 25 and 40, 45 and 

 60, etc., position 1 and 4, respectively, of the depth-selector and starting-frequency switches may be 

 used to the limit of the sounding range of the supersonic system, assuming that the bottom is regular 

 enough to warrant the use of the 20-fathom dial. The intervening ranges, in fathoms, of 20 to 25, 40 

 to 45, 60 to 65, etc., correspond to periods of paralysis of the echo amplifier caused by the transmission 

 of the signal. The paralysis range is not necessarily exactly 5 fathoms but should be considered as 

 such to avoid any possibility of error due to the paralysis. The alternate paralysis ranges, in fathoms, 

 of 20 to 25, 60 to 65, 100 to 105, etc., can be accommodated on positions 2 and 4 of the two switches as 

 indicated in the second line of table 15. The remaining paralysis ranges, in fathoms, of 40 to 45, 80 

 to 85, etc., require positions 3 and 4 of the two switches. 



This latter switch arrangement, depth-selector switch on position 3 and starting-frequency switch 

 on position 4, will accommodate the ranges, in fathoms, of 40 to 100, 110 to 200, 210 to 300, etc., to the 

 limit of the sounding range of the supersonic system. The paralysis ranges, in fathoms, of 100 to 110, 

 300 to 310, etc., are accommodated by placing the two switches on positions 4 and 4, but the range of 

 200 to 210 fathoms requires the use of the 1,000-fathom cutout switch. Best results will be obtained 

 in this range by placing the two switches on positions 3 and 4, and manually deleting two consecutive 

 signals of every four index revolutions by means of this 1,000-fathom cutout. Such a cycle is repre- 

 sented by the next to last column in table 15. From the above discussion the rest of the table will be 

 apparent. 



The ranges in this table represent actual depths of water and consequently values that will be 

 registered on the dials, for an average draft of the transceiver has already been taken into consideration 

 in all numbers in the first 10 columns. When the shoal-normal switch is placed on the shoal position 

 the instrument will dependably measure depths of 2 fathoms. 



Table 16 is given to illustrate the functioning of the Dorsey Fathometer No. 3. For example, 

 the fourth and fifth lines in this table convey the information that if supersonic operation with regis- 

 tration on the 20-fathom dial is desired, the depth-selector and starting-frequency switches should be 

 placed on positions 1 and 4 or on 2 and 4, the choice being made according to table 15. Furthermore, 

 from table 16 the elements and parts connected and used in the various circuits may be determined for 

 different switch settings, and the number of signals transmitted per second is given. The reference 

 numbers appearing in this table under the heading "Circuits used" refer to the corresponding elements 

 or parts listed and described in table 14. These reference numbers in tables 16 and 17 do not refer to 

 terminal posts and should not be confused with the numbers used to designate them. 



