My explanation is valid only for 2D sonar, NOT SI/DI....
Technically, the ping rate for the transducer is hard-coded in the firmware.
And is coded to offer the best possible number of returns for a given depth.
From my non-scientific test, the ping rate is about 30 pings par second (for single beam) from 0-30 feet.
Divide that by two if you are using Dual Beam sonar. (Since HB use the same crystal for 200 and 83, the unit must wait for the 200 kHz return before pinging the 83 kHz. They should use different crystals to double the speed of data to the unit)
And slow down to around 5 pings/second at 200 feet. (always Single Beam)
Here's a little table:
Feet - Pings
10 - 29.4
20 - 29.4
30 - 29.4
40 - 25
50 - 20
60 - 16.9
70 - 14.9
80 - 12.8
100 - 10.3