Velocity calculations
The change in velocity (dv) is given by
dv=-(1500/2)*df/f
df - change in frequency
f - transmitted frequency
the soundspeed is divided by 2 because of transmission both ways in the water.
(1) The accuracy of the Aquadopp Profiler is 1% of measured value +/-0,5cm/s.
The +/- 0,5cm/s part is caused by the transmitting pulse related to drift of the clock.
Using the formula above this leads to an allowance in frequency of
600kHZ : +/- 40 Hz
1MHz : +/- 66.67 Hz
2MHz : +/- 133,33 Hz
(2) Again, using the above formula 1m/s correponds to a frequency of
600kHZ : (600000-800)Hz = 599200 Hz
1MHz : (1000000-133,33)Hz = 999866,67 Hz
2MHz : (2000000-266,67)Hz = 1999733,33Hz
dv=-(1500/2)*df/f
df - change in frequency
f - transmitted frequency
the soundspeed is divided by 2 because of transmission both ways in the water.
| Quote |
| (1) How much is the allowance of transmitting frequency? How many kHz do you allow in transmitting frequency for 1MHz Aqd Profiler ? And for 2MHz instrument, for 600kHz instrument as well ? (2) How do you convert received frequency to current velocity ? (when sound speed is assumed to be 1500m/s) In case of 1MHz Aqd Profiler, to how many frequency change does correspond current speed of 1m/s ? And in case of 2MHz and of 600kHz ? |
(1) The accuracy of the Aquadopp Profiler is 1% of measured value +/-0,5cm/s.
The +/- 0,5cm/s part is caused by the transmitting pulse related to drift of the clock.
Using the formula above this leads to an allowance in frequency of
600kHZ : +/- 40 Hz
1MHz : +/- 66.67 Hz
2MHz : +/- 133,33 Hz
(2) Again, using the above formula 1m/s correponds to a frequency of
600kHZ : (600000-800)Hz = 599200 Hz
1MHz : (1000000-133,33)Hz = 999866,67 Hz
2MHz : (2000000-266,67)Hz = 1999733,33Hz
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