Fluke FLK-8808A [98/100] Fluke direc

8808A

Users Manual

A-8

Making Low-Level Current Measurements

There are many applications where obtaining the utmost accuracy in low-level current

measurements is critical. For example, determining the leakage current of a battery

operated device in its standby mode is critical in determining the time before battery re-

charge is needed. Traditional multimeters make these measurements using a shunt

method shown in Figure A-3. The shunt resistor converts the current to be measured to a

voltage, which is called the burden voltage. Since the internal impedance of the current

source is in parallel with the shunt resistor, the current flowing in the shunt resistor is less

than the actual value, thus causing an error.

OUT

SHUNT

Internal

eue28.eps

Figure A-3. Shunt Method of Low-Level Current Measurement

Another method of low-current measurement is the feedback resistor method shown in

Figure A-4. The feedback resistor converts the current to be measured into a voltage. The

high gain operational amplifier forces the burden voltage to approximately zero and thus

reduces the error associated with the simple shunt measurement approach. The zero

burden voltage measurement method used in the Meter gives a more accurate

measurement of low-level (leakage) currents.

OUT

Feedback

Internal

eue29.eps

Figure A-4. Zero Burden Voltage Low-Level Current Measurement

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