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2.1.5 Signal Transmission (CONT-A, CONT-B Boards)
Refer to the block diagram on page 2-2.
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Echo, Depth and Temperature Data Reading by CPU
The eight bit echo data (256 step slices) from the TRS. A board are once applied to the
dual-port RAM and finally transferred to the CPU. When writing the echo data into CPU, the
sampling interval is controlled depending on the distance from the transmitter unit as
shown in Table 2.1. In shorter ranges the data are picked up at shorter intervals to improve
resolution. For example, in case of 320m range, the total sampling data are;
l
0----------5----------10----------20----------40---------------------------320 m range
512 + 256 + 256
Table 2.1
Range
0 - 5 m
5 - 10 m
10 - 20 m
20 - 40 m
40 - 640 m
The echo data read by CPU is compressed logarithmically from 8 bits to 4 bits and stored
in scratch pad RAM U2 until they are read out for signal transmission. This logarithmic
conversion enhances the low-level signals so that they may be less affected by noise
during transmission toward the paravane receiver. If, for example, the noise level in the
propagation path is as in Fig. 2.12, the signals within "b" are affected by noise in the linear
conversion while those only within "a" are affected in the logarithmic conversion.
Fig. 2.11 Temperature Data (TP8)
+ 256
3840 x 280/600 = 3072
Sampling Interval
1 cm
2 cm
4 cm
8 cm
16 cm
2-7
l
Total Echo Data
512
256
256
256
3840
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