YOKOGAWA TB830D, Руководство пользователя, Страница: 13 / 85

<1. OVERVIEW>
1-6
IM 12E04B40-02EN 1st Edition : Mar. 08, 2023-00
1.6 Measurement principle
TB830D is a surface scattering turbidity detector.
It is comprised of a Flow cell, Detection unit, and Smart unit.
The sample flowing in from the lower side of the Flow cell overflows at the upper part of the Flow cell.
At the same time, the LED light source of the sealed Detection unit irradiates the light beam to the
sample surface through the plural lenses.
The irradiated light is divided into transmitted light, reflected light, and scattered light at the liquid
surface.
Transmitted and reflected light disappears in a dark room equivalent to a blackbody.
The intensity of the scattered light (L) is proportional to the turbidity as shown in the following
equation.
Ls = K · Q · S
Where:
K: Constant due to turbidity
Q: LED light intensity
S: Turbidity
The scattered light is converged by the lens inside the Detection unit to be detected by a light-
receiving element (silicon photodiode).
The Detection unit incorporates a comparator to detect LED light intensity.
The lens of the Detection unit has a built-in transparent heater to prevent the effect of condensation.
The Smart unit controls the light source drive circuit based on the signal from the comparator so
that LED light intensity (Q) keeps constant.
Turbidity is calculated by performing arithmetic on the basis of the turbidity signal from the light-
receiving element (silicon photodiode).
The Smart unit also functions as a power supply for measurement, memory storage of parameters
such as calibration parameters, and a communication device between the detector and the converter.
Reflected
light
Detection unit
Flow cell
Transmitted
light
Drain
Sample
Comparator
Lens with heater
light-receiving element (silicon photodiode)
Scattered
light
Plural lenses
Light source
（ LED ）
Lenses
（ with heater ）
Amp.
Amp.
AD
CPU
Detector I/O
（ digital ）
Light source
drive circuit
Smart unit
Figure 1.3 Measurement principle