Example 9: depth - derivation of depth from pressure

This derived channel implements a simplified equation for water depth in meters, 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 RBRconcerto 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".
• ρ 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 meters.

Example commands:

( Confirm the channel type ) 

( Request confirmation of everything ) 

( Request, then change, the programmed water density )