Keithley 6487, Reference Manual

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2-12 Measurement Concepts and Connections Model 6487 Reference Manual
Floating measurements
Figure 2-9 shows an example where the Model 6487 floats.
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Before attempting floating measurements, make sure to have a thor-
ough understanding of any dangers involved. Take adequate precau-
tions before connecting any instruments or power sources. Also, make
sure to read and understand information contained in
“Connection
fundamentals,” page 2-2 . Death or injury due to electrical shock can
result if adequate safety measures are not taken.
The maximum safe voltage between picoammeter LO and chassis
ground (common mode voltage) is 505V. The Model 6487 does not
internally limit the LO-to-chassis voltage. Exceeding 505V can create a
shock hazard.
If it is possible for the DUT or external supply to present more than
505V to the input HI, it is imperative that the connection between
input LO and the external voltage source be sufficiently low impedance
and capable of carrying the short-circuit current of the source, in order
that the LO not exceed 505V.
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Connecting COMMON or ANALOG OUT to earth while floating the
input may damage the instrument.
The LO-to-chassis breakdown voltage is 505V. Exceeding this voltage
may cause damage to the instrument.
Figure 2-9
Floating measurements
20V
R
1
20V
A
+
–
R
2
6487
Picoammeter
R
3