Precision Measurement Engineering, Inc.
Precision Measurement Engineering, Inc.
The SCAMP computes depth from measurements of ambient pressure made using the SCAMP's pressure sensor. Depth is computed from pressure by knowing the density of the surrounding water. The SCAMP is supplied with calibration coefficients for fresh water. These are computed for the pressure - depth relation:
depth (Meters) = 0.7030696 * pressure (PSI)
If depth is desired for different density, seawater for example, then an equation such as the one above must be determined. Each of the C's (C0, C1, C2, C3) in the SCAMP Control Dialog Channel Tab the depth channel must be multiplied by the ratio of the coefficient in the new depth-pressure relation divided by 0.7030696.
For example, if the SCAMP is used in sea water of 35 ppt at 15 deg C, then density is shown in sigma-T tables:
| density (d) = | 1.02599 gm/cm**3 |
| acceleration of gravity (g) = | 980.621 cm/sec**2 (sea level) |
| conversion constant = | 1.45034E-5 PSI per dyne/cm**2 |
| pressure = | density * acceleration of gravity * depth |
| C0' = | C0 / (d * g * 100 * 1.45034E-5 * 0.7030696) |
| C1' = | C1 / (d * g * 100 * 1.45034E-5 * 0.7030696) |
| C2' = | C2 / (d * g * 100 * 1.45034E-5 * 0.7030696) |
| C3' = | C3 / (d * g * 100 * 1.45034E-5 * 0.7030696) |
Note that the pressure sensor makes errors of a few tenths of a percent. Very slight
density corrections such as the change in density of fresh water with temperature will not
make significant contributions to the overall depth channel error.