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ZENER_PROTECTS_METER

2016-09-26 10:07  
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ZENER_PROTECTS_METER
Simple overvoltage protection circuit makes 10-V zener conduct when voltage E1 being measured goes over 20-V full-scale limit of voltmeter using milliammeter movement with multiplier resistor R2. This turns on Q1, drawing current through LED to give visual indication of overvoltage, while providing protective shunt path around meter.-H. Olson, Sensitive Meters Saved, 73 Magazine, Oct. 1977, p 153.