A variety of testing equipment, such as biochemical analyzers, hemocytometers, and blood gas analyzers, all have negative pressure devices, which play the role of sample suction, reagent suction, and waste liquid extraction. In work, we often encounter negative pressure systems. Failure caused. Example 1 Negative pressure failure of KX-21 blood cell analyzer of Japan East Asia Company Turn on the power, after the instrument is initialized, enter the work screen, occasionally an error alarm appears, the screen prompts "Replace diluent", but after replacing the diluent, the fault is still there. According to the above analysis, the fault maintenance takes one by one elimination method. First check the diluent, the amount is sufficient, no problem; second, measure the float switch with a multimeter. Between the lower position of the float and the upper position of the float, the resistance value changes from infinity to zero, indicating that the float switch is working properly. Then carefully observe the fault phenomenon, and find that the liquid level in the buffer bottle rises very slowly when pumping. Therefore, it is possible to determine that the possibility of CPU damage is very small, and focus on checking that the negative pressure in the buffer bottle is insufficient. The negative pressure in the bottle is provided by the original negative pressure of the compressor. The original negative pressure value is directly measured with a negative pressure meter at -50mmHg. Completely normal. According to the piping diagram, the original pressure is introduced into the buffer bottle all the way, and the SVR is also introduced all the way to drive the cylinder, so it is suspected that there is occasional air leakage during the work. We repeated the specimens to reproduce the fault, and then used soapy water to check the leaks of each part of the air joint one by one, obviously there was a leak at the center of the cylinder driving the SVR shaft cylinder, carefully disassemble the cylinder, and found that it was a sealed O-shaped Caused by aging deformation of the ring. This O-ring can be found on the market as an alternative, and the price is only a few cents. After replacement, the instrument is fully functional. Example 2 Hitachi 7020 automatic biochemical analyzer negative pressure failure After conducting several sample tests, it was found that a large amount of liquid in the reaction cup overflowed on the reaction tray. There was no error alarm on the instrument screen, but the measurement could not be continued. The failure analysis carefully observes that it is the liquid remaining at the A nozzle of the 13 nozzles of the cleaning arm, and the A nozzle is to suck the reaction liquid after the measurement, so it is judged that the negative pressure of the A nozzle is insufficient. From the analysis of the pipeline diagram, the cause of the failure is: â‘ the suction nozzle is blocked; â‘¡ there is a leak in the pipeline; â‘¢ the solenoid valve SV3, SV11, SV14 does not work â‘£; the vacuum pump is faulty. In view of the above analysis, fault maintenance also adopts one-by-one elimination method. Because the remaining negative pressure steps are normal, you can eliminate the failure of the vacuum pump; after cleaning the nozzle with the 0.5mm stainless steel wire provided, the failure is still the same, so you can eliminate the nozzle clogging; check the inlet tube of the negative pressure buffer bottle It is found that there is negative pressure, so it can be eliminated that the solenoid valve SV11, SV14 and the previous level of pipeline leakage, check the buffer bottle without rupture leakage, preliminary judgment is that the solenoid valve SV3 is not working, use a multimeter to measure its working voltage DC 24V Normal, it is suspected that the solenoid valve is rusted, and the solenoid valve is removed. At this time, it is found that the small piece of silicone tube connecting the buffer bottle and the solenoid valve has broken. The original problem lies here. After replacing the silicone tube, the instrument returns to normal. Maintenance summary Although these two cases of negative pressure failures have different instruments, the causes of their failures are similar. If you encounter a negative pressure failure of the inspection equipment, if you do not analyze it carefully, it is easy to misinterpret it as an electrical component such as a negative pressure pump or solenoid valve. The fault will be repeated after an expensive replacement. When servicing, you should carefully compare the piping diagram, first of all, focus on eliminating pipeline leakage, so as to avoid detours and eliminate faults as soon as possible. DC Livestock Farming Industrial Actuators,AC Livestock Farming Industrial Actuators,Livestock Farming Industrial Linear ActuatorsFarm Ventilation 24VDC Linear Actuator TOMUU (DONGGUAN) ACTUATOR TECHNOLOGY CO., LTD. , http://www.tomuu.com
Failure analysis The KX-21 blood cell meter diluent detection sensor is a float switch. Under normal circumstances, the diluent from the outside of the machine is drawn into the internal buffer bottle. The solenoid valves SV-1 and SV2-2 are instructed to work first. A negative pressure is formed inside, so that the dilution of the buffer bottle rises to a certain height within a specified time, so that the float triggers the liquid level switch to turn on, and sends a signal to the CPU: but if the liquid level does not reach the required level within the specified time, the CPU If the diluent level switch-on signal is not detected, the instrument will prompt “Dilution replacement†error. Therefore, the following conditions will cause this failure: ①insufficient dilution; ② insufficient negative pressure added to the buffer bottle; ③ failure of the float switch; ④ failure of the CPU board.