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7Edition
th

Low Level Measurements Handbook

Precision DC Current, Voltage,
and Resistance Measurements
Low Level
Measurements
Handbook
Precision DC Current, Voltage,
and Resistance Measurements

SEVENTH EDITION
Contents
SECTION 1 Low Level DC Measuring Instruments
1.1 Introduction ............................................................................................... 1-3
1.2 Theoretical Measurement Limits .......................................................... 1-3
1.3 Instrument Definitions ............................................................................ 1-5
1.3.1 The Electrometer ......................................................... 1-5
1.3.2 The DMM ......................................................................1-7
1.3.3 The Nanovoltmeter .......................................................1-7
1.3.4 The Picoammeter ......................................................... 1-8
1.3.5 The Source Measure Unit Instrument ......................... 1-8
1.3.6 The Low Current Preamp ............................................ 1-9
1.3.7 The Micro-ohmmeter ................................................... 1-9
1.3.8 The Low Current Source ............................................. 1-9
1.4 Understanding Instrument Specifications ....................................... 1-10
1.4.1 Definition of Accuracy Terms .....................................1-10
1.4.2 Accuracy ......................................................................1-11
1.4.3 Deratings .....................................................................1-15
1.4.4 Noise and Noise Rejection ..........................................1-15
1.4.5 Speed ..........................................................................1-17
1.5 Circuit Design Basics ............................................................................. 1-17
1.5.1 Voltmeter Circuits .......................................................1-17
1.5.2 Ammeter Circuits ........................................................1-19
1.5.3 Coulombmeter Circuit ................................................1-23
1.5.4 High Resistance Ohmmeter Circuits ..........................1-24
1.5.5 Low Resistance Ohmmeter Circuits............................1-26
1.5.6 Complete Instruments ............................................... 1-28

SECTION 2 Measurements from High Resistance Sources
2.1 Introduction ............................................................................................... 2-2
2.2 Voltage Measurements from High Resistance Sources ................... 2-2
2.2.1 Loading Errors and Guarding...................................... 2-3
2.2.2 Insulation Resistance of the Test Circuit ....................2-11
2.3 Low Current Measurements ................................................................ 2-15
2.3.1 Leakage Currents and Guarding ................................2-15
2.3.2 Noise and Source Impedance .....................................2-21
2.3.3 Zero Drift ................................................................... 2-23
2.3.4 Generated Currents ................................................... 2-23
2.3.5 Voltage Burden ...........................................................2-31

Low Level Measurements Handbook iii
2.3.6 Overload Protection ................................................... 2-33
2.3.7 AC Interference and Damping ................................... 2-34
2.3.8 Using a Coulombmeter to Measure Low Current ..... 2-35
2.4 High Resistance Measurements ......................................................... 2-39
2.4.1 Constant-Voltage Method........................................... 2-40
2.4.2 Constant-Current Method ......................................... 2-41
2.5 Charge Measurements.......................................................................... 2-46
2.5.1 Error Sources ............................................................. 2-47
2.5.2 Zero Check ................................................................. 2-48
2.5.3 Extending the Charge Measurement Range
of the Electrometer .................................................... 2-48
2.6 General Electrometer Considerations............................................... 2-49
2.6.1 Making Connections .................................................. 2-50
2.6.2 Electrostatic Interference and Shielding ....................2-51
2.6.3 Environmental Factors............................................... 2-55
2.6.4 Speed Considerations ................................................ 2-56
2.6.5 Johnson Noise ............................................................ 2-62
2.6.6 Device Connections ................................................... 2-66
2.6.7 Analog Outputs .......................................................... 2-69
2.6.8 Floating Input Signals .................................................2-70
2.7 High Impedance Measurement Optimization Summary.............. 2-71

SECTION 3 Measurements from Low Resistance Sources
3.1 Introduction ............................................................................................... 3-2

3.2 Low Voltage Measurements ................................................................... 3-2
3.2.1 Effects of Error Sources on Voltage Measurements .... 3-2
3.2.2 Thermoelectric EMFs ................................................... 3-3
3.2.3 Internal Offsets ............................................................ 3-7
3.2.4 Zero Drift ..................................................................... 3-7
3.2.5 RFI/EMI ........................................................................ 3-9
3.2.6 Johnson Noise .............................................................3-10
3.2.7 1/f Noise ......................................................................3-11
3.2.8 Line Cycle Interference and Line Cycle Integration .. 3-12
3.2.9 Magnetic Fields .......................................................... 3-13
3.2.10 Ground Loops .............................................................3-14
3.2.11 Ways to Reduce Noise .................................................3-16
3.2.12 Common-Mode Current and Reversal Errors ............3-17

iv
3.3 Low Resistance Measurements.......................................................... 3-18
3.3.1 Lead Resistance and Four-Wire Method .................... 3-18
3.3.2 Thermoelectric EMFs and
Offset Compensation Methods .................................. 3-20
3.3.3 Non-Ohmic Contacts ................................................. 3-25
3.3.4 Device Heating ........................................................... 3-26
3.3.5 Dry Circuit Testing ..................................................... 3-27
3.3.6 Testing Inductive Devices .......................................... 3-28
3.4 Measurement Optimization Summary for
Low Impedance Measurements ......................................................... 3-29

SECTION 4 Applications
4.1 Introduction .............................................................................................. 4-2

4.2 Applications for Measuring Voltage from
High Resistance Sources ........................................................................ 4-2
4.2.1 Capacitor Dielectric Absorption ................................. 4-2
4.2.2 Electrochemical Measurements .................................. 4-6
4.3 Low Current Measurement Applications ........................................... 4-9
4.3.1 Capacitor Leakage Measurements .............................. 4-9
4.3.2 Low Current Diode Measurements .......................... 4-13
4.3.3 Low Current Measurements of MOSFETs...................4-16
4.3.4 Light Measurements with Photomultiplier Tubes ..... 4-18
4.3.5 Ion Beam Measurements .......................................... 4-21
4.3.6 Photoconductive Current of PIN Photodiode ........... 4-23
4.3.7 Avalanche Photodiode Reverse Bias Current
Measurements ............................................................ 4-24
4.3.8 Current-Voltage Characterization of
Carbon Nanotube (CNT) FETs .................................. 4-26
4.4 High Resistance Measurement Applications .................................. 4-28
4.4.1 Surface Insulation Resistance Testing of
Printed Circuit Boards .............................................. 4-28
4.4.2 Resistivity Measurements of Insulating Materials .... 4-30
4.4.3 Resistivity Measurements of Semiconductors .......... 4-34
4.4.4 Voltage Coefficient Testing of High Ohmic
Value Resistors .......................................................... 4-44
4.5 Charge Measurement Applications .................................................. 4-45
4.5.1 Capacitance Measurements ...................................... 4-45

Low Level Measurements Handbook v
4.5.2 Using a Faraday Cup to Measure Static Charge
on Objects ................................................................. 4-46
4.6 Low Voltage Measurement Applications ........................................ 4-48
4.6.1 Standard Cell Comparisons ...................................... 4-48
4.6.2 High Resolution Temperature Measurements
and Microcalorimetry ............................................... 4-50
4.6.3 Hall Voltage and Resistivity Measurements
of a Six-Terminal Bridge Sample ................................ 4-53
4.7 Low Resistance Measurement Applications .................................. 4-54
4.7.1 Contact Resistance .................................................... 4-54
4.7.2 Superconductor Resistance Measurements .............. 4-57
4.7.3 Resistivity Measurements of Conductive Materials .. 4-59

SECTION 5 Low Level Instrument Selection Guide
5.1 Introduction ............................................................................................... 5-2
5.2 Instrument and Accessory Selector Guides........................................ 5-2

APPENDIX A Cable and Connector Assembly

APPENDIX B Glossary

APPENDIX C Safety Considerations
Test System Safety ................................................................................... C-2
General Safety Considerations ............................................................. C-2

INDEX

vi
SECTION 1

Low Level DC
Measuring
Instruments
FIGURE 1-1: Standard Symbols Used in this Text

Prefixes
Symbol Prefix Exponent
y yocto- 10