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Model 6485 Picoammeter Instruction Manual Applications Guide I-13

Figure I-10

Range change voltage transients

NOTE The current that can be inadvertently delivered to the DUT is limited by an

internal resistance. This internal resistance varies as the range is changed. For

example, manually up-ranging from 2

A to the 20

A range can never deliver

more than 10V/50kΩ = 200

A to the DUT. This current will be further limited

by any impedance of the DUT.

Up-range input response

Figure I-11 illustrates the type of transient voltage that can be expected when up-ranging

with a full-scale input signal (200µA signal on 200µA range, up-range to 2mA range).

Both the magnitude and duration of this voltage are reduced for lower current ranges. The

current limit imposed by the R

is also greatly reduced. The polarity depends on the polar-

ity of the input current. Figure I-11 was measured with a positive input current.

6485 Picoammeter

Transient

Range being R

changed to:

2mA, 20mA 500W

20mA, 200mA 50kW

200nA, 2mA5MW

2nA, 20nA 500MW

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