User`s manual

Section 5: Configure Menu, Part III - Calibration Coefficients
59
Transmissometer Calibration Coefficients
• Sea Tech, Chelsea (Alphatracka), and WET Labs Cstar
Enter M, B, and path length (in meters)
Path length (distance between lenses) is based on sensor size
(for example, 25 cm transmissometer = 0.25m path length, etc.).
light transmission (%) = M * volts + B
where
M = ( Tw / [W0 – Y0] ) ( A0 – Y0 ) / ( A1 – Y1 )
B = - M * Y1
and
A0 = factory voltage output in air (factory calibration from transmissometer
manufacturer)
A1 = current (most recent) voltage output in air
Y0 = factory dark or zero (blocked path) voltage (factory calibration from
transmissometer manufacturer)
Y1 = current (most recent) dark or zero (blocked path) voltage
W0 = factory voltage output in pure water (factory calibration from
transmissometer manufacturer)
Tw = % transmission in pure water
(for transmission relative to water, Tw = 100%; or
for transmission relative to air, Tw is defined by table below.
Tw = % Transmission in Pure Water
(relative to AIR)
Wavelength 10 cm Path Length 25 cm Path Length
488 nm (blue) 99.8% 99.6%
532 nm (green) 99.5% 98.8%
660 nm (red) 96.0 - 96.4% 90.2 - 91.3%
Transmissometer Example
(from calibration sheet) A0 = 4.743 volts, Y0 = 0.002 volts,
W0 = 4.565 volts
Tw = 100% (for transmission relative to water)
(from current calibration) A1 = 4.719 volts and Y1 = 0.006 volts
M = 22.046
B = - 0.132
Note: SEASAVE can process data for an instrument interfacing
with up to two transmissometers in any combination of Sea Tech,
Chelsea Alphatracka, and WET Labs Cstar, when using the New
Style configuration.
• WET Labs AC3
This sensor requires two channels - one for fluorometer voltage (listed
under fluorometers in the dialog box) and the other for transmissometer
voltage (listed under transmissometers). Make sure to select both when
configuring the instrument.
Enter Ch2o, Vh2o, VDark, and X from calibration sheet.
Beam attenuation = {[log (Vh2o - VDark) - log (V - VDark)] /X} + Ch2o
Beam transmission (%) = exp ( -beam attenuation * X) * 100
Note:
See Application Note 7 for
complete description of
computation of M and B.