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OPERATION
Each intersecting
point in the matrix is called a crosspoint
that can be individually
closed or opened by programming
the Model
707 mainframe.
The crosspoints
for rows A
through F are configured
for 2-pole switching,
as shown
in Figure 2-13. For these rows, SIGNAL
and GUARD are
switched separately to any of the 12 columns on the card.
The crosspoints for rows G and H use l-pole switching,
with only SIGNAL being switched. The equivalent circuit
for this arrangement
is also shown in Figure 2-13.
2.6.2 Row and Column
Isolators
In order to maintain
the integrity
of the low-current
and
CV pathways, isolator relays are incorporated into each col-
umn. These isolators are indicated as small circles on the
matrix diagram of Figure 2-13. Each relay remains open un-
til a crosspoint located in rows C through H is to be closed.
In this manner, the general-purpose
pathways are isolated
from the more critical low-current
and CV pathways.
In a similar manner, row isolator relays isolate the cross-
point relays from a given row to minimize
leakage current
and capacitance, and maximize path resistance. The row
-
isolator relay closes when any crosspoint relay associated
with that row is closed.
2.6.3 Pathway
Considerations
As discussed previously,
the eight rows on the matrix card
are designed for different
purposes.
Rows A and B are
designated low-current
mws, rows C through F are general
purpose rows, and rows G and H are CV rows.
Many of the specifications
for the card differ among row
types. For example, the offset current for the low-current
rows is <lpA,
but the general purpose and CV rows have
a higher offset current of 2OpA. Thus, A and B would be
the rows of choice for low-current measurements. Also, the
path isolation for rows A and B is an order of magnitude
higher than that the other rows (lo'% vs. lO'*Q
Again,
these two rows would
be preferable
for very
high-
impedance
measurements.
In summary,
the following
general rules apply when
choosing which rows to use for specific measurements:
l
Use rows A and B for low-current
measurements.
l
Use rows
A,
B, G, and
H for
low-capacitance
measurements.
l
Rows A and B should be used where high path isola-
tion resistance is of primary
concern.
l
Rows A and B have the largest bandwidth,
while rows
G and H have the smallest bandwidth.
For more detailed information
on these factors, refer to the
Model
7072 Specifications
located at the front of this
manual.
2.6.4 Internal
Matrix Expansion
Two to six Model 7072 cards can be connected together
within
the mainframe
to yield an 8 X N matrix, where N
depends on the number of cards. Figure 2-14 shows an in-
ternally expanded matrix with three cards, resulting in an
8 x 36 (eight row by 36 column) matrix. As summarized
in Table 2-3, the actual column number used when pro-
gramming
the unit is determined
by the slot.
Z-20
I
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