Example 9: depth - derivation of depth from pressure

This derived channel implements a simplified equation for water depth in metres, in which no account is taken of either geographical variations in the Earth's gravitational field, or the variation of water density with depth: both these quantities are treated as constants, although the water density can be changed using the "settings density" command.

In the form used by the logger, using an RBRconcerto³ C.T.D as an example, this becomes:

where

• n0 is the index of the pressure channel, 3 in this case,

• n1 is the index of the atmospheric pressure channel; not present in this example, so set to "value".

• p is the value set for the density of water using the "settings density" command, g is a fixed constant 0.980665, representing the standard value of acceleration due to gravity, in units which correctly account for pressures being measured in decibars,

• Dm is the calculated depth in metres.

Examples

>> calibration 4 type
<< calibration 4 type = dpth01

Confirm the channel type.

>> calibration 4
<< calibration 4 type = dpth01, datetime = 20171201000000, n0 = 3, n1 = value

Request confirmation of all calibration coefficients.

>> settings density
<< settings density = 1.026021
>> settings density = 1.0197
<< settings density = 1.0197

Request, then change, the programmed water density.