Liquid surface safety alarm circuit with thermistors

Published:2011/8/26 2:10:00 Author:Jessie | Keyword: safety alarm, thermistors | From:SeekIC

This circuit inputs voltage U8 is added to thermistorsthrough protection resistor . U7 and U6's action thresholdsare formedby bleeder. If liquid surface sensor isin air, its cooling decrescent surface absorbs little, input voltage U8 increses, but it is lower than threshold of U6. So integrated circuit output terminal C is connected, send out empty signal. At the same time, it flows thorugh the Dalindun transistor BD646 which makes the filling valve open. When thermistors liquid surface sensor dipped into the liquid, drain current increases, Rv's voltage drop increases, U8's voltage ris educed to U7's threshold, output A connects lamp L1, and it will show box full signal. When sensor isin short circuit, it will produce above-mentioned switch positions. But when sensor is disconnected, input voltage U8 increases to power voltage, higher than threshold.



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