2-6 Measurement Concepts Model 6485 Picoammeter Instruction Manual
Basic connections to DUT
Connections
Basic connections are shown in Figure 2-3, the DUT is the current to be measured. Circuit
high is connected to the center conductor of the input connector and circuit low is con-
nected to the connector’s shell.
Figure 2-3
Basic connections
WARNING 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 Current limiting resistors are required for DUTs capable of forcing
voltages 220V or greater. Damage to the instrument may result if volt-
ages greater than 220V are forced on the Model 6485 Input HI.
Voltages greater than 220V
Often, when making resistance measurements, it is necessary to use an external voltage
source with voltages greater than the maximum tolerable input voltage of 220V. In the
event that the resistance to be measured becomes shorted, or an incorrect value of resis-
tance is inserted in the test setup, the voltage source can permanently damage the Model
6485. To prevent this damage, the following steps should be taken as a protection precau-
tion. (An alternate protection method is described in “Measuring high resistance with
external bias source,” page I-19, for cases not requiring the maximum sensitivity of the
6485.)
HI
LO
DUT
INPUT*
* Maximum Continuous Input Signals
220V Peak, DC to 60Hz sine wave
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