VOLTMETERS, CLAMPING

HOW DO I 'CLAMP', OR LIMIT A DC MILLIAMP METER TO READ A SPECIFIC RANGE OF VOLTAGES.

EXAMPLE: 12V SOURCE, WANT METER TO READ RANGE FROM 10V TO 16 V ONLY! WHY? I NEED TO READ 12-14 VOLTS CENTER SCALE.


THANKS FOR HELP

MIKE C.

 

The easiest method I can think of off the top of my head is to put a 10V Zener diode in series with the meter circuit. As long as the Zener is reverse biased, (band toward the positive voltage) current will be blocked until voltage exceeds 10V. Normal ohms law calculations for spanning the meter will then apply with the 10 Volt offset desired. Note, subtract the 10V dropped across the Zener before calculating the series meter resistor.