Lake Shore Model 370 AC Resistance Bridge User’s Manual
TABLE OF CONTENTS
Chapter/Paragraph Title
Page
1 INTRODUCTION .................................................................................................................................................... 1-1
1.0 GENERAL
......................................................................................................................................... 1-1
1.1 DESCRIPTION .................................................................................................................................. 1-2
1.2 SENSOR
PERFORMANCE............................................................................................................... 1-5
1.3 SPECIFICATIONS
............................................................................................................................. 1-9
1.4 SAFETY
SUMMARY ....................................................................................................................... 1-11
1.5 SAFETY
SYMBOLS ........................................................................................................................ 1-11
2 BACKGROUND
...................................................................................................................................................... 2-1
2.0 GENERAL
......................................................................................................................................... 2-1
2.1
USEFUL TEMPERATURE RANGE ................................................................................................... 2-1
2.2 TEMPERATURE SCALES ................................................................................................................ 2-1
2.3
CRYOGENIC COOLING SYSTEM TERMINOLOGY ........................................................................ 2-1
2.3.1 Dilution
Refrigerator Terminology .................................................................................................. 2-2
2.3.2
3
He Cryostat ................................................................................................................................... 2-3
2.3.3 Adiabatic
Demagnetization Refrigerator (ADR) .............................................................................. 2-4
2.4
MODEL 370 THEORY OF OPERATION ........................................................................................... 2-5
2.4.1
Why is the Model 370 called a Bridge? .......................................................................................... 2-5
2.4.2 Resistance Measurement .............................................................................................................. 2-5
2.4.3 Excitation
Modes
............................................................................................................................ 2-6
2.4.4 Resistance Ranges ........................................................................................................................ 2-6
2.4.5 Measurement Circuit ...................................................................................................................... 2-6
2.4.5.1 Shielding
and Grounding Theory ................................................................................................ 2-7
2.4.5.2 Shields........................................................................................................................................ 2-7
2.4.5.3 Electrical Isolation ...................................................................................................................... 2-7
2.4.5.4 Driven Guards ............................................................................................................................ 2-7
2.4.5.5 Active
Common Mode Reduction ............................................................................................... 2-8
2.4.5.6 Matched
Impedance Current Source .......................................................................................... 2-8
2.4.6 Measurement
Speed and Filtering ................................................................................................. 2-8
2.5 NOISE
SOURCES
............................................................................................................................. 2-9
2.5.1 Induced
Electrical Noise ................................................................................................................ 2-9
2.5.2 Ground
Loop Noise ........................................................................................................................ 2-9
2.5.3 Analog
Circuit Noise ...................................................................................................................... 2-9
2.5.4 Digital
Circuit Noise ........................................................................................................................ 2-9
2.5.5 Resistor
Thermal Noise ............................................................................................................... 2-10
2.5.6 Interference
Between Two Model 370s ........................................................................................ 2-10
2.5.7 Vibration
Noise
............................................................................................................................. 2-10
2.6 MEASUREMENT ERROR ............................................................................................................... 2-10
2.6.1
Warm Up and Temperature Drift .................................................................................................. 2-10
2.6.2 Resistor
Installation ...................................................................................................................... 2-10
2.6.3 Resistor
Self-Heating and Thermal Resistance ........................................................................... 2-11
2.6.4 Lead
Resistance .......................................................................................................................... 2-11
2.6.5 Current Leakage .......................................................................................................................... 2-11
2.6.6 Cable
Capacitance ....................................................................................................................... 2-11
2.6.7 Instrument Operation ................................................................................................................... 2-12
2.7 OPERATING
TRADEOFFS ............................................................................................................. 2-12
2.7.1
Resistor Self-heating vs. Excitation .............................................................................................. 2-12
2.7.2 Excitation
vs.
Signal-to-Noise ...................................................................................................... 2-13
2.7.3 Signal-to-Noise
vs.
Measurement Bandwidth .............................................................................. 2-13
2.8
MODEL 3716/L and 3708 SCANNER ............................................................................................. 2-13
2.8.1 Scanner
Performance .................................................................................................................. 2-14
2.8.2 Controlling
Temperature While Scanning .................................................................................... 2-14
2.9 TEMPERATURE
MEASUREMENT
................................................................................................. 2-14
2.9.1 Sensor
Selection .......................................................................................................................... 2-14
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