What is an automatic particle counter
Abstract: Introduce the principle, detection method, application and precautions of an automatic particle counter. Excerpt from "Hydraulic Pneumatics and Sealing"
1 Introduction
Statistics at home and abroad show that 70% to 85% of hydraulic lubrication system failures are caused by oil particle pollution, so the problem of oil particle pollution has attracted considerable attention in the hydraulic lubrication industry, and the monitoring of oil is also It seems very necessary. In the hydraulic lubrication system, the particle size in question is in the range of 0.5~200μm, and the most critical is 5~15μm. Generally, particles are divided into two types: soft and hard. Soft particles include the agglomerates of fillers and water, the decomposition of basic components of oil and polymers, lint fibers, etc., which can surround the surface of the heat exchanger to reduce heat dissipation. Ability to cause the system to heat up; due to the blockage and deposition of soft particles in the dynamic gap of the component, the valve core jams and malfunctions; the fiber can adhere to the filter screen, orifices, and nozzles and trap debris. Hard particles include chips brought in during the manufacturing process, particles invaded in the maintenance and working environment, and wear products and oxides in the system.
These hard particles are the most harmful. Larger particles can cause sudden failures, and smaller ones can cause erosion and wear or blockage to block the valve core. In short, it can accelerate the wear of the components and cause the components to fail. The wear caused by pollutant particles includes cutting wear, fatigue wear, adhesive wear, and erosion wear. At present, there is an automatic particle counter that can effectively monitor pollutant particles. Its appearance is shown in Figure 1. A brief introduction to it is given below.
2 The principle of automatic particle counter
Automatic particle counters mainly include shading type, light scattering type and resistance type, etc. The measuring range can be 0.5~9000μm. Common automatic particle counting uses the shading principle. The shading type automatic particle counter uses a shading type sensor. The light type sensor is composed of a light source, a sensing area window, a photodiode, a preamplifier, and a counting processor. The light source is an incandescent bulb or a laser diode that emits a parallel beam and transmits The sensing area window is made of transparent optical material, the oil flow flows from the middle in the vertical direction, the photodiode converts the received light energy into a voltage signal, and the preamplifier and counting processor are the collected voltage signals. The size and number of pollutant particles are judged by comparison. The principle diagram of the shading sensor is shown in Figure 2. The light source from the incandescent bulb or laser diode passes through the transparent sensing area window and irradiates the photodiode. When the oil in the transparent sensing area has polluting particles passing through, The amount of light received on the photodiode is reduced, and the amount of blocked light is proportional to the size of the pollutant particle. By calibrating with standard pollutants, the output voltage of the photodiode-the relationship between the size of the pollutant particle can be obtained, so that the pollution can be distinguished. The particle size, the counting processor counts according to the particle size level.
Most of the automatic particle counters currently in use are single-laser automatic particle counters. The pollutants from 4μm to 68μm are detected by a photodiode, and its range is large, so its detection accuracy will be affected. In order to solve this problem, some automatic particle counters use dual laser technology, which greatly improves the detection accuracy and repeatability. The principle diagram of the dual-laser automatic particle counter is shown in Figure 3.One of the single-point high-precision lasers is used to measure pollutants less than 6μm, and the other standard-precision laser is used to measure between 6μm and 68μm. Contaminants, and using the unique optical path and photodiode of the dual laser beams, by measuring the number of particles in 8 particle size distribution sections (>4, 6, 14, 21, 25, 38, 50, 68μm), the super High-precision results and excellent repeatability.
The detection principle of the automatic particle counter is introduced above. A specific automatic particle counter is composed of a light-shielding sensor system, a pressure reducing valve, a flushing valve, a slow-speed servo cylinder, and an output device. The working principle diagram of the dual laser automatic particle counter is shown in Figure 4. The shading sensor system is the core component of the automatic particle counter. Its performance determines the quality of the automatic particle counter; the pressure reducing valve is used to reduce the system. After passing through the pressure reducing valve, the pressure of the system maintains a constant value, ensuring that the input pressure of the slow servo cylinder is a constant value, so that the slow servo cylinder can accurately measure the flow; the function of the flush valve is flushing, closing test, Turn on the drain, etc., to flush the system before the test, so as to ensure that the test is not affected by the last test, the test result is true, and cross contamination is avoided; the slow servo cylinder is used to accurately measure the volume of oil entering the test Since the standard of oil cleanliness is the total number of particles in a certain volume, it is very important to accurately measure the volume of oil entering the test; the output devices mainly include printers, computer output interfaces, etc., for printing test results Or let the computer save the test results, the test results generally adopt ISO4406, NAS1638, SAE4059 and other standards.
3 Automatic particle counter detection method
The detection methods of automatic particle counter mainly include online quick test, online routine test, online dynamic test, oil sample/bottle test, continuous working test, etc.
(1) Online quick test
Online test is performed only once, and an 8 mL oil sample is tested. The typical test time is less than 2 min.
(2) Online routine test
Only conduct one online test, test a 15 mL oil sample, the routine test time is less than 3 minutes.
(3) Online dynamic test
Precise triple oil sample test, continuous analysis of 3 online oil samples, average the results, the oil sample volume is 24 mL, the test analysis time is less than 5 min.
(4) Oil sample/bottle test
Perform an "offline" test on the selected oil sample. The equipment used is an optical sampling bottle with a capacity of 110 mL of mineral oil and a capacity of 250 mL of mineral oil or phosphate esters.
(5) Continuous working test
The automatic particle counter can automatically sample and analyze a hydraulic lubrication system continuously according to a set time interval. The time interval can be 1 to 30000 min.
4 Application of automatic particle counter
Automatic particle counter mainly has the following applications.
(1) Online inspection (or monitoring) of important hydraulic lubrication systems (or equipment) can reduce labor costs, eliminate the influence of human factors, obtain accurate oil cleanliness, and find problems as early as possible to facilitate timely resolution of problems To achieve proactive preventive maintenance of hydraulic lubrication systems (or equipment), reduce failures, reduce downtime losses, and increase working life.
(2) As an offline testing tool, the hydraulic lubrication components produced are inspected regularly, and the oil is cleaned or replaced in time when contamination is found to ensure that the produced products meet the requirements of the specified cleanliness.
(3) As a service tool, it provides paid service for units that have not purchased an automatic particle counter but have this service requirement.
(4) Installed in airplanes, automobiles or construction machinery, monitor its oil at any time, and set alarm points as required, and start the operation of the cleaning filter device after alarming.
(5) It is used in the cyclic filtration and purification of large hydraulic systems without personnel monitoring. As long as the set cleanliness requirements are reached, the automatic particle counter will send a signal to automatically stop the cyclic filtration.
(6) is used in military equipment to monitor and operate precise hydraulic lubrication systems, enhancing self-confidence in hostile environments.
(7) As the testing equipment of laboratories or scientific research units, it provides scientific researchers with accurate cleanliness reports and provides accurate scientific basis for experiments and scientific research.
5 Precautions for the use of automatic particle counter
When using the automatic particle counter, pay attention to the following aspects.
(1) Before the automatic particle counter is used for the first time, charge it for at least 16 hours to make the nickel-cadmium battery full; the nickel-cadmium battery should be discharged once a month, discharged, and then recharged for 16 hours, so as to maintain the nickel-cadmium battery Good charging effect, prolong the service life of the battery.
(2) Do not use acetone or similar solvents as the cleaning agent, otherwise, when cleaning the inside of the automatic particle counter or cleaning the sampling bottle, the seal will be damaged. Petroleum ether should be used as the cleaning agent.
(3) When the online sampling hose is connected to the pipeline of the hydraulic system to be measured, it should be noted that the measured oil pressure must be less than the maximum pressure specified by the automatic particle counter, otherwise the automatic particle counter will be damaged, but it must not be less than the automatic particle counter. Minimal pressure, otherwise the test cannot be completed.
(4) Never connect the oil discharge hose of the automatic particle counter to any pressure pipe, otherwise, pressure will enter the oil discharge pipe, causing the instrument to malfunction or even be damaged. The waste oil discharged by the automatic particle counter can only be discharged into the waste oil collection bottle or into other containers that are open to the atmosphere.
(5) Before the automatic particle counter performs the test, open the flush valve to flush the instrument for at least 1 min, or flow more than 200 mL of oil to remove the air in the automatic particle counter and the remaining oil from the previous test. Cross contamination to ensure the accuracy of test results.
(6) In order to ensure that the test results provided by the automatic particle counter are accurate and consistent, it must be checked regularly. Because the calibration uses special particles for testing, it must be calibrated with the help of modern scanning electron microscope and image analysis technology.Therefore, only when the manufacturer of the automatic particle counter or its designated unit has the ability to control the automatic The particle counter is checked.
(7) The sampling bottle and sampling equipment should be clean and free of pollution. If too much air is mixed into the oil sample, the test result will be inaccurate, and it must be vacuumed to eliminate the air before the test.
(8) The automatic particle counter requires the fluid to be tested to be translucent and homogeneous. It cannot be used to test the cleanliness of emulsions, two-phase liquids, liquid mixtures, aqueous oils, gas oils and other liquids.
6 Conclusion
With the rapid development of electronic technology, automatic particle counters have been widely used in oil cleanliness detection. It has the advantages of fast counting speed, high accuracy, and easy operation.
references:
[1]Lu Yongxiang. Manual of Hydraulic and Pneumatic Technology[M]. Beijing: Mechanical Industry Press, 2002.
[2] Xia Zhixin. Hydraulic system pollution control[M]. Beijing: Mechanical Industry Press, 1992.
[3]Hu Bangxi. Cleanliness control of hydraulic lubrication system[M]. Beijing: Metallurgical Industry Press, 2003.
[4] MP FILTRI product sample.
About the author: Zhu Xiaoming (19672), male, from Nankang, Jiangxi, graduated from Gansu University of Technology in 1988, majoring in fluid transmission and control, as an engineer, engaged in the application of hydraulic systems and hydraulic components.