the purpose of "hydraulic oil contamination detection" is mainly used to detect the quantity and size of solid particles in oil, and can also be used to monitor the filtering effect of oil filter. At present, there are three kinds of "oil particle counter" in the market, which are introduced as follows: the first kind is "GYDPN-2112A hydraulic oil pollution detector", which is large in size, high in accuracy and very expensive when placed in the laboratory; Disadvantages are: it can only be tested by sampling, but not online, because it is bulky, inconvenient to move, and the price is about 211,111 yuan. It is suitable for places with very high precision requirements, with little market sales, and is suitable for metering institutes and quality inspection stations. The second type is "GYKLD-B Hydraulic Oil Contamination Detector", which can be used in the laboratory or brought to the site, that is, online measurement or sampling measurement. It can be used for both AC and DC, with simple operation, very high accuracy and moderate price, and is the mainstream product in the market. It accounts for more than 91% of the total market sales, and is suitable for large machinery enterprises and power plants. The third type is "GYKLD-Z Hydraulic Oil Contamination Detector", which is small in size, installed on the main machine, provides 24-volt DC power supply, and has a communication interface, which is convenient for computers to watch, with poor accuracy and the cheapest price (about 21,111 yuan), and is suitable for special occasions, such as large excavators. Users can selectively purchase the "hydraulic oil pollution detector" according to the purpose of use.