555 pointer electronic megohmmeter

Published:2011/9/18 21:14:00 Author:Ecco | Keyword: 555 , pointer electronic megohmmeter | From:SeekIC

As shown in Figure 8-19, the megohmmeter uses the electronic boost circuit as measuring power, the range is 0.5 ~ 1000MΩ. IC1 and R1, R2, C1 are connected in non-steady-state oscillation mode, and the oscillation frequency f = 1.44 / (R1 +2 R2) C1, it is about 15kHz. Transformer T is the step-up transformer, the secondary induced voltage is rectified by D1, after being filtered, it can get 1000V DC high voltage power supply as measuring voltage, the current limiting resistor R5 and the measured resistor are connected in series and then form measuring loop with header. Dial readings can be calculated by the following formula, the current value of the corresponding label: I = V / (R + R5 + Rg), and V is the voltage on C5, Rg is the internal resistance of meter, R is the dial reading. RP1 header is used for for streaming on the 100μA header, correcting 2mA full-scale, and measuring low resistor with 0.5 ~ 10MΩ.



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