MULTIMETER_CONDUCTANCE_ADAPTER

Published:2009/7/16 3:44:00 Author:Jessie | From:SeekIC

A 1.000-V reference is buffered by IC1, a TLC271, and is connected to J1 for use when measuring conductance. The voltage reference is derived from IC3, a 1.25-V temperature-compensat ed band-gap reference. The current drop developed by the component under test at J1 and J2 is converted by IC2 to an output voltage that can be displayed on a digital voltmeter. The output voltage is limited to a maximum of 2.0V and a minimum of 1.0 V. With the inverting input of IC2 at virtual ground, the maximum input current that can be measured is -2.0 μA. In reading the conductance of an unknown resistor (labeled RX, in the figure), -1.0 V is applied to J1, with J2 being at virtual ground. Based on the maximum input current that can be converted by IC2, the smallest resistance that can be measured is 500,000Ω. The values chosen for the circuit generate a conductance reading of 1.0 μmho/V, or 1.0 nmho/mV output. A 1.0-MΩ resistor will have a conductance of 1.0 pmho, or 1000 nmho. A 1.0-GΩ resistor would have a conductance of 1.0 nmho. The current-to-voltage conversion is set by R10, which gives an output of 1 V/μA, or 1 mV/nA. The lowest tolerance you should use for R10 is 1 percent.



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