Analysis and repair of temperature control fault phenomenon in Shanghai | high-speed centrifuge centrifuge

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Problem representation: Shanghai centrifuge spindle rotation and found its indicating normal, vacuum system operation and indicator is normal, but the temperature indicator is wrong, the automatic control failure, the boot, the refrigeration system is not work, while the temperature indicator is minus 2O degrees, in fact, the cavity is normal room temperature.
Analysis: from the problems reflected that, should belong to the temperature sensor and indicator system of doubt. In order to find faults location, according to the physical, making the temperature sensing and indicating electrical principle diagram (some of the instruments did not give the electrical principle diagram), analysis, faults may produce in the temperature sensor uA-741 operational amplifier, indicator or centrifuge chamber (thermistor) three on some. The itemized check, discover thermistor R circuit, the resistance being infinite, because it is a negative temperature coefficient of resistance is greater, indicating that the lower the temperature.
Repair: a thermistor selection of plastic compression technique is sealed in a plastic probe, thermistor is located at the top of a probe, the two leads origin intermediate leads, the other one is a bare copper wire, plastic pressure in plastics. Replace with a probe to, immediately able to troubleshooting, we take the self-control method, solves the question. Thermistor borrowed from the other units in the same type of centrifuge, measure the typical temperature - its resistance characteristic curve, Shanghai centrifuge suggestions according to this selected MF type thermistor, Xi'an radio 22 factory produced by the selection, select thermistor fundamental symbol of the characteristic curve, adjusted by means of standard resistance box, through repeated adjustments, the thermistor access circuit, and then check the thermometer, the difference can be at L-2 DEG C.