YOKOGAWA TB820D, User Manual, Page: 37 / 87

<4. SETTING PARAMETERS>
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IM 12E01B30-02EN 2nd Edition : June 09 , 2021-00
[How It Functions]
To suppress a sudden fluctuation due to air bubbles or dust, the TB820D:
(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 averaging 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;
(6) during that period, suspends the Air noise detection value check.
If the value returns to the original value in a short time, it is judged as a bubble and the value
is held for the Air denoising hold time.
If the value remains changed for a certain period of time, it is judged that the measured
value has changed, not a bubble, and the hold is released.
(7) averages signals without the Air noise detection value check for a specified Denoising
release time period and gives turbidity readings;
(8) after the Denoising release time has elapsed, performs the Air noise detection value check
again.
[Instructions for Use]
The air denoising function is effective in processes where turbidity changes are relatively small
under normal conditions, but it may not be suitable for processes where sudden changes
occur often. Even if sudden changes do not usually occur, this function may be activated and
may cause a delay in the response of the reading or output if stepwise turbidity changes occur
occasionally. Therefore, before using this function carefully consider the process conditions,
and in order to use it properly, determine optimum setpoints for the operating conditions while
changing them little by little.
When using the function, pay attention to the following.
(1) Adjust the Air noise detection value according to the degree of reading change due to air
bubbles or dust.
(2) If an excessively long Air denoising hold time is set, the turbidimeter may not be able to
detect a change in reading that may have occurred and should have been recognized as a
real change.
(3) If the function is responsible for the delay in the response of the turbidity reading, try setting
the Denoising release time longer without changing the Air denoising hold time.
(4) When an abnormal turbidity reading is suspected, turn off the function once and wait for
a while and see. The function may have prevented the turbidimeter from giving readings
properly.