Keithley 6485 - Page 16

I Applications Guide
Measurement considerations ...................................................... I-2
Leakage currents and guarding ........................................... I-2
Input bias current ................................................................. I-3
Voltage burden ..................................................................... I-3
Voltage offset correction procedure ............................. I-4
Noise and source impedance ............................................... I-5
Source resistance .......................................................... I-5
Source capacitance ....................................................... I-6
Electrostatic interference and shielding .............................. I-7
Shielding vs. Guarding ............................................... I-10
Making connections .......................................................... I-10
Typical range change transients ........................................ I-12
Up-range input response ............................................ I-13
Down-range voltage transients are smaller ................ I-14
Steps to minimize impact of range change transients ....... I-15
Run test with a fixed range. ........................................ I-15
Down-range by starting at highest
current necessary ........................................................ I-15
Using protection circuitry .......................................... I-16
Reduce up-ranging transient ...................................... I-16
Zero check on / off response ............................................. I-16
Applications .............................................................................. I-18
Diode leakage current ........................................................ I-18
Capacitor leakage current .................................................. I-19
Measuring high resistance with external bias source ........ I-19
Cable insulation resistance ................................................ I-21
Surface insulation resistance (SIR) ................................... I-22
Photodiode characterization prior to dicing ...................... I-22
Focused ion beam applications .......................................... I-25
Using switching systems to measure
multiple current sources .................................................... I-26