2-12 Measurement Concepts Model 6485 Picoammeter Instruction Manual
Figure 2-7
Capacitor test circuit with protection
Floating measurements
Figure 2-8 shows an example where Model 6485 floats.
WARNING 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 2-3. 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 42V. The Model 6485 does not inter-
nally limit the LO-to-chassis voltage. Exceeding 42V can create a
shock hazard.
If it is possible for the DUT or external supply to present more than
42V 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 42V.
CAUTION Connecting COMMON or ANALOG OUT to earth while floating the
input may damage the instrument.
The LO-to-chassis breakdown voltage is 500V. Exceeding this voltage
may cause damage to the instrument.
Protection Circuit
HI
6485
Picoammeter
LO
Capacitor
Under Test
S
V
D1
D2
A
R
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