YOKOGAWA TB830D, User Manual, Page: 38 / 85

< 4. SETTING PARAMETERS >
4-3
IM 12E04B40-02EN 1st Edition : Mar. 08, 2023-00
4.1.3 Meas. damping time constant, Maint. damping time
constant
Performing time constant processing smooths the fluctuation of measured turbidity. 63%
Response time is set as a time constant.
The larger the time constant is, the more stable the value of turbidity becomes, but the slower the
response is.
In a measurement mode, the measurement damping time constant is applied. Maintenance time
constant is used under the following conditions:
• Maintenance mode
• During Calibration
• Automatic cleaning/Automatic zero calibration
To make the response faster under the above period, set the maintenance damping time
constant to a smaller value than the measurement damping time constant.
4.1.4 Turbidity warning High/Low limit
Set the High or Low limit of the turbidity value.
If the value exceeds the limit, a warning appears. A “Turbidity warning High limit” is generated
when the setup upper limit is exceeded, and a “Turbidity warning Low limit” is generated when
the lower limit is exceeded.
4.1.5 Air denoising setting
n
Overview
Air bubbles or dust in a sample may cause fluctuation in turbidity readings; generally, a sudden
rise in reading occurs. The fluctuation is dependent on the size of air bubbles or dust and their
behavior.
It is recommended that a head tank for removing air bubbles be installed. (A TB830D with a
sampling system is equipped with a head tank.). A head tank prevents air bubbles from reaching
the detector. In rare cases, however, air bubbles occur and grow in the pipe between the head
tank and the detector, and rise to the measuring cell, resulting in reading fluctuation.
The air denoising function is to detect and suppress a sudden change due to air bubbles or
dust. The detector has a time constant processing (measurement time constant) for turbidity
signal. The time constant can be varied. Increasing the measurement time constant can handle
the indicated changes caused by small bubbles and debris to some extent. However, when the
measurement time constant is too large, setup with a very large time constant is not practical
because the response of the turbidity signal itself is slow according to the measurement time
constant. Therefore, TB830D detects only sudden changes caused by bubbles and dust, and
suppresses sudden changes caused so as not to be output to the display and power outputs.
[Function]
To suppress a sudden fluctuation due to air bubbles or dust, the TB830D:
(1) Checks a turbidity signal before averaging;
(2) Calculates the difference between the current signal and the previous signal;
(3) Compares the difference with the Air noise detection value;
(4) If it is less than the Air noise detection value, proceeds to average and gives the turbidity
reading;
(5) If it is greater than the Air noise detection value, holds the output for a specified Air denoising
hold time period; During this time, is displayed to the main screen. No contact output
occurs by the Air denoising hold time period.