LED Module Calibration Strategy to Improve Measurement Accuracy of TRO Concentration

Gwang-Ho Lee,Do-Hyun Kim,Sung-Shin Kim,Min-Soo Kim,Hee-Je Kim

doi:10.3390/electronics10192410

Abstract

In order to limit various alien species by ballast water, electrolysis of ballast water is used to sterilize microorganisms. In this process, total residual oxidizer (TRO) is produced, and it is necessary to measure the precise TRO concentration to prevent excessive disinfection by-products and limit emissions. In this TRO concentration measurement system, a white LED module and RGB sensor are used to measure the absorbance through the DPD colorimetric method. The intensity of LED light has a little error for each LED module. In addition, the effect of LED aging in which the intensity of the light source decreases with the elapsed time. For this reason, the TRO concentration measurement error increases. To solve this problem, we propose an LED module calibration algorithm by current PI control and an optimal LED operation time derivation to reduce the effect of LED aging. A large number of LED modules were applied to various seawater environments. In the conventional method, the measurement accuracy and precision of the average TRO concentration were 6.56% and 9.54%, respectively, and measurement accuracy and precision through the proposed algorithm and LED aging optimization were greatly reduced to 0.10% and 0.85%, respectively. In addition, we derived that LED aging was minimized when the measurement time of LED light was 1 s and the turn-off time of the LED light was 10 s. Through these experimental results, we confirmed that the non-uniform LED light is improved by the proposed algorithm. Furthermore, the standard values for TRO concentration measurement (accuracy: less than 5%, precision: less than 2%) were satisfied.

Highlights

We know that the influx of alien species caused by the movement of ballast water to balance ships with the increase of international trade causes serious problems in the marine ecosystem [1,2]
The electrolysis method Ballast Water Management System (BWMS) must control the current to generate an appropriate Total Residual Oxidant (TRO) to prevent sterilization and excessive disinfection by-products in accordance with International Maritime Organization (IMO) D-2 regulations
We propose a new calibration strategy for LED modules to improve the measurement accuracy of TRO concentration

Summary

Introduction

We know that the influx of alien species caused by the movement of ballast water to balance ships with the increase of international trade causes serious problems in the marine ecosystem [1,2]. The electrolysis method BWMS must control the current to generate an appropriate TRO to prevent sterilization and excessive disinfection by-products in accordance with IMO D-2 regulations For this reason, it is important to measure the correct TRO concentration. If the green and blue wavelengths are used among these types of wavelengths, it is possible to measure the TRO concentration with more than double accuracy even at high concentration (over 10 mg/L) [18,19] In these semiconductor devices, an output error of the light source and a sensing error of the RGB sensor were made due to the manufacturing process, durability, and environmental factors [20].

Conventional TRO Concentration Measurement Method and Problems

Strategies to Improve Measurement Accuracy for TRO Concentration

The Solution about LED Aging Effect

Findings

Conclusions