it seems that I have answered you once, so let me talk about the online instrument brands I have seen. In addition to Coetzee, WTW, Shimadzu, DKK and HORIBA, the following are some online monitors for COD and ammonia nitrogen that have been certified by the Testing Center of National Environmental Monitoring Center, Guangzhou Yiwen, Beijing Puxi General Instrument Factory. Here are some certified by Beijing Puxi General Instrument Co., Ltd., Guangzhou Yiwen Technology Co., Ltd., Shandong Evergrande Environmental Protection Co., Ltd., Hebei Xianhe Technology Development Co., Ltd., Beijing Maoda Environmental New Technology Co., Ltd., Bluestar Water Treatment Technology Co., Ltd., Beijing Huanke Environmental Technology Company, Beijing Huanyu Hongye Technology Development Co., Ltd., Beijing Zhonghuanfa Environmental Technology Group, Nanjing Delin Environmental Protection Instrument Co., Ltd., Jiangsu Luye Environmental Protection Technology Instrument Co., Ltd., Lanzhou Lianhua Environmental Protection Technology Co., Ltd., Hunan Zhicheng Technology Development Co., Ltd., Wuhan Taiken Environmental Protection Technology Development Co., Ltd., Hubei Intercontinental Environmental Protection Engineering Technology Co., Ltd., Hebei Asia-Pacific Environmental Technology Development Co., Ltd., Sichuan Huitong Technology Industry Co., Ltd., Nanjing Huadu Environmental Protection Equipment Co., Ltd., Shimadzu (Hong Kong) Co., Ltd., Shengli Oilfield Longfa Industry and Trade Co., Ltd., Shijiazhuang Gaode Environmental Technology Co., Ltd., Jiangsu Jiangfen Power Analysis Instrument Co., Ltd., Hunan Lihe Technology Development Co., Ltd., American HACH Company, Shanghai Precision Scientific Instrument Co., Ltd., Jiangsu Dongheng Group High-tech Industry Co., Ltd. (information given by former boss)