66
13.3
Definition of Oxygen Units
phase shift
dphi
The phase shift dphi is the fundamental unit measured by the
optoelectronics in the
FireStingGO
2
. The measuring principle is
based on a sinusoidally modulated red excitation light, resulting in
a phase-shifted sinusoidally modulated emission in the NIR. This
phase shift is measured and converted into oxygen units based on
the Stern-Vollmer-Theory. Please note that dphi is not at all
linearly dependent on the oxygen units, and increasing oxygen
levels correspond to decreasing dphi values, and vice versa! As a
thumb of rule, anoxic conditions will give about dphi=53, whereby
ambient air will give about dphi=20 for full range oxygen sensors.
partial pressure p
O2
hPa = mbar
Used in:
gas and water
For a calibrated sensor, the partial oxygen pressure p
O2
in units of
hPa (equivalent to mbar) is the fundamental oxygen unit measured
by the
FirestingGO
2
.
partial pressure p
O2
Torr
Definition:
p
O2
[Torr] = p
O2
[hPa] x 759.96 / 1013.25
Used in:
gas and water
volume percent p
V
%O2
Definition:
p
v
= p
O2
[hPa] / p
atm
x 100%
Used in:
gas
with p
atm
: actual barometric pressure
% air saturation A
%air sat.
Definition:
A[%air sat.] = 100% x p
O2
/ p100
O2
Used in:
water
