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Many instruments incorporate internal filtering that may help reduce EMI effects. In some
cases, additional external filtering may be required. Keep in mind, however, that filtering may
have detrimental effects on the measurement.
Ground loops
When two or more instruments are connected together, care must be taken to avoid unwanted
signals caused by ground loops. Ground loops usually occur when sensitive instrumentation is
connected to other instrumentation with more than one signal return path such as power line
ground. As shown in
Figure 3-7
, the resulting ground loop causes current to flow through the
instrument LO signal leads and then back through power line ground. This circulating current
develops a small but undesirable voltage between the LO terminals of the two instruments. This
voltage will be added to the source voltage, affecting the accuracy of the measurement.
Figure 3-8
shows how to connect several instruments together to eliminate this type of ground
loop problem. Here, only one instrument is connected to power line ground. Ground loops are
not normally a problem with instruments having isolated LO terminals. However, all
instruments in the test setup may not be de-signed in this manner. When in doubt, consult the
manual for all instrumentation in the test setup.
Instrument 1
Instrument 2
Instrument 3
Power Line Ground
Signal Leads
Ground Loop
Current
Figure 3-7
Power line ground
loops
Instrument 1
Instrument 2
Instrument 3
Power Line Ground
Figure 3-8
Eliminating ground
loops
3-22
Operation
Summary of Contents for 2000-Scan
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Page 13: ...1 General Information General Information ...
Page 17: ...2 CardConnections andInstallation CardConnec tionsandInstal lation ...
Page 35: ...3 Operation Operation ...
Page 58: ...3 24 Operation Section 3 Page 24 Tuesday July 8 2003 2 30 PM ...
Page 59: ...4 Service Information Service Information ...
Page 73: ...5 Replaceable Parts Replaceable Parts ...
Page 76: ...5 4 Replaceable Parts ...
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Page 79: ...A Specifications Specifica tions ...
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