Keithley 2790, Reference Manual, Page: 65 / 568

2-8 Model 2790 SourceMeter
®
Switch System Reference Manual
Figure 2-1
7702 2-wire system channel connections to Model 2790 DMM
4-wire functions (paired channels)
A 4-wire function, such as
Ω
4, requires that another measurement channel be paired to the
system channel. For example, if the switching module has 40 measurement channels,
channels 1 through 20 can be used as the system channel, while channels 21 through 40
are used as the paired channel. For a switching module that has 40 measurement channels,
channel 1 is paired to channel 21, channel 2 is paired to channel 22, channel 3 is paired to
channel 23, and so on.
Figure 2-2 shows an example of system channel connections for a 4-wire function.
Assume a Model 7702 switching module is installed in slot 2 of the mainframe and a
4-wire function, such as
Ω
4, is selected. When channel 201 is closed using the system
channel close keys, the Channel 1 relay and the input backplane isolation relay
(Channel 45) closes to connect the channel to DMM Input. Also, the Channel 21 relay and
the sense backplane isolation relay (Channel 44) close to connect the paired channel to
DMM Sense. Also note in
Figure 2-2 that the Channel 43 relay closes to isolate channel 1
from channel 21.
The complete simplified schematic of Model 7702 is provided in Figure 2-13 .
DMM
Model 7702 Switching Module
Model 2790
Slot 2
System channel operation:
Close channel 201
Channel 1
Relay
HI
LO
HI
LO
Input
Channel 45
Backplane
Isolation
Relay
Channel 1