Keithley 2750, Руководство пользователя

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2-22 Close/Open Switching Module Channels Model 2750 Multimeter/Switch System User’s Manual
Dual independent multiplexers
Using multiple channel operation, any multiplexer switching module can be configured as
two independent multiplexers. For example, the Model 7700 is normally used as a single
1
×
20 multiplexer, but it can also be configured as two 1
×
10 multiplexers.
NOTE Thermocouple temperature measurements using the internal or external refer-
ence junction cannot be performed when using multiple channel operation to
connect an input channel to the DMM. The simulated reference junction will
instead be used resulting in invalid readings (“ERR” annunciator turns on). See
“Temperature measurements,” page 3-25 , for details.
A multiplexer switching module is configured as two multiplexers by using multiple chan-
nel operation to close the 2-pole/4-pole relay. The Model 7700 is configured as two inde-
pendent multiplexers by closing channel 23. As shown in
Figure 2-8 , the closed position
of channel 23 isolates Multiplexer A (channels 1 through 10) from Multiplexer B (chan-
nels 11 through 20).
For the dual multiplexer configuration, only Multiplexer A channels can be internally con-
nected to the DMM of the Model 2750. For the Model 7700, closing channel 25 allows
channels 1 through 10 to be measured by the DMM.
When using the dual multiplexer configuration, the sense backplane isolation relay must
be kept open to isolate Multiplexer B channels from the sense terminals of the DMM. For
the Model 7700, channel 24 must be kept open (
Figure 2-8 ).
Figure 2-8
Dual multiplexer configuration (Model 7700)
Ch 1
Ch 10
Ch 11
Ch 20
Ch 23
(Closed)
Ch 24
Ch 25
Multiplexer A
(1x10)
Multiplexer B
(1x10)
For the dual multiplexer configuration,
Ch 23 must be closed, and Ch 24 must
remain open.
HI
LO
HI
LO
Channels
2–9
HI
LO
Channels
12–19
HI
LO
Sense
HI
LO
Input
To
Model 2750
DMM
HI
LO
2750-900-01.book Page 22 Wednesday, August 3, 2011 7:56 AM