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2-34
The Model 7702 can accommodate 4-wire measurements by using channel pairs. Primary
channels 1 through 20 become paired to channels 21 through 40. For example, with the Ω4
function selected, channel 1 becomes paired to channel 21. For example, when you close
channel 1, channel 21 will also close.
The 2-wire functions include DCV, ACV, DCI, ACI, Ω2, CONT, FREQ, PERIOD, and
TEMP (thermistor). The 4-wire functions/operations include Ω4, TEMP (4-wire RTD),
RATIO, and CH AVG (ratio and channel average are covered in
With a 4-wire function/operation selected, channels are paired as follows:
CH1 and CH21
CH2 and CH22
CH3 and CH23
CH4 and CH24
CH5 and CH25
CH6 and CH26
CH7 and CH27
CH8 and CH28
CH9 and CH29
CH10 and CH30
Schematic diagram
The simplified schematic diagram of the Model 7702 is shown in
through 40 are used for all measurements except amps. Channels 41 and 42 are used for
amps only.
There are two backplane relays (channels 44 and 45) to connect the input channel(s) to the
backplane of the Model 2790. With a 2-wire function (except amps) selected, channel 45
will close; and with a 4-wire function selected, both channels 44 and 45 will close.
There is a 2-pole/4-pole relay (channel 43) between channels 1-20 and channels 21-40.
When a 2-wire function (i.e., DCV) is selected, channel 43 opens (2-pole position) to
allow any of the 40 channels to be connected to the input backplane.
When a 4-wire function is selected, channel 43 closes (4-pole position) to isolate channels
1 through 20 from channels 21 through 40. With a system channel (1 through 20) closed,
its paired channel (21 through 40) will also close to connect the sense channel to the sense
backplane.
For the two current channels (41 and 42), signal HI and LO are routed directly to the back-
plane when the channel is closed.
As shown in
Sense". The Card Input and Card Sense terminals are connected to the inputs of channels
44 and 45 (isolation relays). If channels 1 through 40 are not intended to be connected to
the internal DMM, channels 44 and 45 can be controlled independently using multiple
channel operation.
Model 2790 SourceMeter
CH11 and CH31
CH12 and CH32
CH13 and CH33
CH14 and CH34
CH15 and CH35
CH16 and CH36
CH17 and CH37
CH18 and CH38
CH19 and CH39
CH20 and CH40
Figure
2-13, there are also screw terminals labeled "Card Input" and "Card
®
Switch System Reference Manual
Section
5).
Figure
2-13. Channels 1
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