![background image](http://html2.mh-extra.com/html/keithley/6487/6487_user-manual_3951658089.webp)
B-2
General Measurement Considerations
Measurement considerations
The following measurement considerations apply to all precision measurements.
lists all measurement considerations and indicates where to find detailed information on
them.
For additional measurement considerations, see Appendix G of the Model 6487 Reference
Manual. For comprehensive information on all measurement considerations, refer to the
Low Level Measurements handbook, which is available from Keithley.
Ground loops
Ground loops that occur in multiple-instrument test setups can create error signals that
cause erratic or erroneous measurements. The configuration shown in
duces errors in two ways. Large ground currents flowing in one of the wires will encounter
small resistances, either in the wires or at the connecting points. This small resistance
results in voltage drops that can affect the measurement. Even if the ground loop currents
are small, magnetic flux cutting across the large loops formed by the ground leads can
induce sufficient voltages to disturb sensitive measurements.
Figure B-1
Power line ground loops
To prevent ground loops, instruments should be connected to ground at only a single point
as shown in
. Note that only a single instrument is connected directly to power
line ground. Experimentation is the best way to determine an acceptable arrangement. For
this purpose, measuring instruments should be placed on their lowest ranges. The configu-
ration that results in the lowest noise signal is the one that should be used. A convenient
way to make this connection uses the ground link at the rear of the Model 6487.
Instrument 1
Instrument 2
Instrument 3
Signal Leads
Ground
Loop
Current
Power Line Ground
Summary of Contents for 6487
Page 13: ......
Page 15: ......
Page 35: ...1 20 Getting Started Model 6487 User s Manual...
Page 47: ...2 12 Connections Model 6487 User s Manual...
Page 61: ...3 14 Measurements and Sourcing Voltage Model 6487 User s Manual...
Page 85: ...7 8 Remote Operation and Commands Model 6487 User s Manual...
Page 86: ...A Specifications...
Page 88: ...B GeneralMeasurement Considerations...
Page 94: ...C ExamplePrograms...
Page 101: ......
Page 103: ......
Page 104: ......