302 
Lecture 16 
TIME (sec) 
\ 2 3 4 5 6 7 8 9 10 7 12 
Transmission 
Fegiage RN Sroa ts Dovates Saba mic 
Receiver ee 
OFF ON 
Echoes s t i 4 f 4 
= ee 
RECORDED 
Fig. 16.1. Coding system of the precision echo-sounder. The diagram is drawn for an echo from ap- 
proximately 1300 fathoms. 
the ship can operate. In the recording system used, the stylus records continu- 
ously, so there is no chance of missing a bottom echo because the stylus is on 
the wrong phase. 
Precision has been obtained by using a precision timed recorder with an 
open scale. Since these recorders are used in many oceanographic instruments, 
including two to be discussed below, they will be described here in some detail. 
They are usually modified facsimile picture receivers; the ones used by N.I.O. 
and described here are part ofthe Mufaxsystem. The stylus consists of a single- 
turn helical blade rotating against a knife edge with chemically impregnated 
paper in between. The point of contact between the helix and the blade starts at 
one edge of the chart, moves across to the other edge, and then immediately 
enters at the first edge again, so that it is always on the chart. Passage of cur- 
rent between the helix and the stylus dissolves some iron from the stylus which 
reacts with the chemicals in the damp paper to form a black mark. The helix is 
driven by a synchronous motor supplied from a tuning fork, so that its rate of 
rotation is precisely controlled. The usual speed is one revolution per second. 
A contact on the helix shaft closes as the writing point moves onto one side 
of the chart and initiates the transmission of the acoustic pulse into the water. 
a ECE, Waters ane echo from eae sea 1 Issel may not return ae after Save 
rear apecryeen rereeeerepeernpsnsennayy erry 
hia ; " ai 
ci nn a I sn nn 
i" H HU a rh A nT 
| A 
m1 I TET Mac Ms aan 
ian or comer | uM 
POE AN ca i 
on i AA: al 
ii A NN GA 
ee 
i at 
i 
AA AAA 
A 
| 
il | 
ic ies 
on | 
i AA Fl | 
Fig. 16.2. A typical nO a taken with the precision echo-sounder. 
