Keithley 4225-RPM, Instructions Manual, Page: 10 / 12

Model 4225-RPM and Model 4225-RPM-LR Remote Pulse Module Instructions
10 PA-1086 Rev. A October 2020
Figure 9: Comparison of load-line effect for 4225-RPM 4225-RPM-LR
The reduction in the load line effect show in the figure above is only available when using the RPM current
ranges (100 nA to 10 mA). When making measurements within these current ranges, the RPM acts as a
preamplifier for pulse current measurements. Above the 10 mA range, the RPM is bypassed and the current
measurement occurs in the 4225-
PMU, which has 50 Ω of output resistance.
When a test requires more than 10 mA of current, the output resistance changes from the 4225-RPM-LR output
resistance (2 Ω to 3 Ω) to the PMU output resistance (50 Ω). Current measurements outside the RPM range
show the typical 50 Ω load-line effect and discontinuity in the curve includes this current measure range
transition.