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LeveLine
®
Instruction Manual
10401-01026 Rev D
6.17. Depth Calculation for Third Party Devices
This section details the method by which sensor depth can be derived from the depth
pressure output from any model of LeveLine
®
probe.
These calculations are automatically carried out in the Aquaread
®
LeveLine
®
Meter and
LeveLink
™
PC Software. If the LeveLine
®
probe is connected to a third party logging or
telemetry device, depth must be calculated by that device or its controlling software.
Depth is calculated using the depth pressure being output from the LeveLine
®
probe, the
local barometric pressure and water density, which is derived from water temperature and
salinity.
Depth_Pressure is output by the LeveLine
®
probes in mB. Temp is output by the LeveLine
®
probes in degrees Centigrade. If the LeveLine
®
probe being used is an ABS type, local
barometric pressure (in mB) must be taken into account.
If the LeveLine
®
probe being used is a GAUGE type, local barometric pressure should be
ignored because it has already been automatically subtracted from the depth pressure in
the probe.
SAL (salinity in PSU) is output by the LeveLine
®
-CTD model probes only. If you are not
using a -CTD probe and do not have access to live salinity data, SAL values of around 0.4
PSU should be used for clean surface water and around 33.0 PSU for sea water.
6.17.1. Water Density Calculation
Constants:
Den_R0 = 3.9863
Den_K03 = -0.00000082467
Den_R1 = 288.9414
Den_K04 = 0.0000000053675
Den_R2 = 68.12963
Den_K10 = -0.005724
Den_R3 = 508.9292
Den_K11 = 0.00010227
Den_K00 = 0.824493
Den_K12 = -0.0000016546
Den_K01 = -0.0040899
Den_K20 = 0.00048314
Den_K02 = 0.000076438
Formulae for calculating water density. First calculate A0, A1 and A2:
A0
= D Den_K01 x Temp + Den_K02 x Temp
2
+ Den_K03 x Temp
3
+ Den_K04 x Temp
4
A1
= D Den_K11 x Temp + Den_K12 x Temp
2
A2
= 1000.0 - (Temp - Den_R0)
2
x (Temp + Den_R1) / (Temp + Den_R2) / Den_R3
Density
= A2 + (A0 x SAL + A1 x SAL
1.5
+ Den_K20 x SAL
2
)
6.17.2. Depth Calculation
Formula for calculating depth in meters using an ABS type probe:
Depth (m)
= (ABS_Depth_Pressure - Baro_Pressure) / (0.0981 * density)
Formula for calculating depth in meters using a GAUGE type probe:
Depth (m)
= GAUGE_Depth_Pressure / (0.0981 * density)
© 2019 Aquaread
®
Ltd.
www.aquaread.com
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