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8842A
Instruction Manual
4-4
3. Allow the displayed reading to settle.
4. Press the OFFSET button.
5. Remove the resistor.
6. Proceed with the desired measurement.
Example:
Measure a 1.5V source with 1 MΩ source impedance, correcting for input bias current.
1. Connect a 1 MΩ resistor between the INPUT HI and INPUT LO terminals.
2. Select the VDC function and the 2V range.
3. Allow the display to settle.
4. Press OFFSET. (This zeroes the input bias current error.)
5. Remove the 1 MΩ resistor.
6. Measure the voltage of the circuit under test.
Note that this procedure does not correct for circuit loading error. Also note that if input
bias current error is not corrected for, it may be added to the circuit loading error.
4-5. RESISTANCE MEASUREMENT
The 8842A allows you to measure resistance in both 2-wire and 4-wire configurations.
Each has its benefits.
4-6. 2-Wire Ohms
Two-Wire ohms measurements are simple to set up and yield good results for most
measurement conditions. Measurements are made as shown in Figure 4-3. An internal
current source (the "ohms current source") passes a known test current (Itest) through the
resistance being tested (Runknown). The 8842A measures the voltage drop across
Runknown, calculates Runknown using Ohm’s law (Runknown = Vtest/Itest), and
displays the result.
f4-03.wmf
Figure 4-3. Wire Ohms Measurement