Fluke NetDAQ 2640A, Service Manual

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NetDAQ
Service Manual
2-50
The channel bits are set to indicate which of the 10 channels within a bank is being
selected. To deselect a channel (so that no channels are selected), write 1111 to the
channel bits. The tree bits should not be deselected, since this would result in excessive
wear of these switches (for the 2640A). Table 2-12: Tree Bits gives the bit patterns for
the tree bits and Table 2-13: Channel Bits gives the bit patterns for the channel bits.
Table 2-12. Tree Bits
Signal TR2 TR1 TR0 Switches
2W Ohms, VAC, Frequency, VDC, <=3V, OTC, TC (CH1-10) 1 0 1 K21, K23
2W Ohms, VAC, Frequency, VDC, <=3V, OTC, TC (CH11-20) 1 1 0 K22, K24
VDC >3V (CH1-10) 0 0 1 K23
VDC >3V (CH11-20) 0 1 0 K24
4W Ohms 1 1 1 K21, K24
Table 2-13. Channel Bits
Channels Enabled CH3 CH2 CH1 CH0
1, 11 0 0 0 0
2, 12 0 0 0 1
3, 13 0 0 1 0
4, 14 0 0 1 1
5, 15 0 1 0 0
6, 16 0 1 0 1
7, 17 0 1 1 0
8, 18 0 1 1 1
9, 19 1 0 0 0
10, 20 1 0 0 1
The time required for the channel switches to settle is given in Table 2-14: Tree and
Channel Switch Settling Times. Note that for both the 2645A and the 2640A, the
switches are guaranteed to have a select time that is longer than their deselect time. This
means that you can select a new channel at the same time as you deselect the previous
channel, without worrying about shorting together the two channels.
Table 2-14. Tree and Channel Switch Settling Times
Description 2640A 2645A
Select 1 ms 150
µ
s
Deselect 1 ms 120
µ
s