Reference data
63
Measuring principle
Two detectors alternately detect transmitted light and scattered light by using two LED light
sources that blink alternately. While Light Source L1 is blinking, Detector D1 detects
transmitted light and Detector D2 detects scattered light. While Light Source L2 is blinking,
Detector D1 detects scattered light and Detector D2 detects transmitted light. The impact of
ambient light is eliminated by causing the light sources to blink and by obtaining the difference
between a turn-on signal and a turn-off signal.
An obtained signal is defined as follows.
Calculate S1/T1 and S2/T2 from the obtained signal.In addition, multiply these results to
obtain a square root given by:
S/T = (S1/T1
∗
S2/T2)
1/2
This S/T has the effect of eliminating the variations of light sources, the variations of detectors,
the damping of light due to local contamination.
S/T obtained when zero water is measured is stored as S0/T0 in the memory.
(S/T-S0/T0) is a relative value. It is multiplied by a coefficient
α
and is span-calibrated to
obtain a standard function value corresponding to the value of turbidity.
Signal
Type
Light source
Detector
T1
Transmitted
light
L1
D1
S1
Scattered
light
L1
D2
T2
Transmitted
light
L2
D2
S2
Scattered
light
L2
D1
S/T
Scattered light S
Transmitted
light T
Signal
amount
Relative
value
Turbidity
