Omega Engineering OMB-DBK-34A, User Manual

Page: 39 / 250

Channel Control and Expansion
In a Daq device or LogBook system, DBK expansion cards and modules can increase the number of analog
input channels from 16 base channels to 256 input channels (16 × 16). The configuration will vary
depending on the DBK’s channel capacity; for example, four 4-channel DBKs or two 8-channel DBKs can
share the same base channel. As part of the multiplexing scheme, each DBK card provides a single output
that must be directed to one of the 16 base channels via the DBK’s JP1 jumper setting.
4
2
2 bits select
1 of 4 gains
2 bits select 1 of 4 gains
4 bits select
1 of 16
inputs
4 bits select 1 of 16 inputs
Daq device System
or LogBook System
Sequencer
100 kHz
Clock
DBK card or module
JP1
channel
select
jumper
2
PGA
16
expansion
channels
MUX
PGA
4
16
base
channels
MUX
P1
P1
ADC
Channel Control and Expansion Block Diagram
The above figure shows the functional parts related to channel control and expansion. An explanation of
the diagram follows.
•
The sequencer selects the channel and gain by controlling multiplexers (MUX) and
programmable gain amplifiers (PGA) in either the LogBook or the Daq device and the DBK.
The sequencer uses 4 expansion address lines to provide 16 unique channel addresses for each
base channel. A 100 kHz clock and user programming of the scan sequence control the
sequencer.
Note : /2000 Series Devices allow for selection of 100 kHz, or 200 kHz internal clock speed via software.
•
The DBK multiplexer selects 1 of 16 (max) channels as directed by the sequencer. The selected
signal travels to the PGA, to the channel-selection jumper, then to the Daq device, or LogBook
via P1.
•
The Daq device or LogBook multiplexer selects 1 of 16 base channels from P1 input lines as
directed by the sequencer. The selected signal goes to the PGA and then to the A/D converter
(A/D).
•
The PGAs can vary the gain on a per channel basis as directed by the sequencer. For DBKs
with a PGA, the sequencer can combine the gains of the DBK PGA and the LogBook or Daq
device PGA for a variety of gain settings.
•
The P1 interface has a signal line for each of the 16 base channels and control lines for gain
setting (pins 5, 6) and sub-channel selection (pins 3, 4, 22, 23).
•
The JP1 channel select jumper in the DBK can be placed on pins for channel 0 through
channel 15. Until the base channel capacity is filled (16 max), multiple cards can use the same
JP1 channel setting if their DIP switches are set to identify unique sub-channel card numbers.
Note : The channel select header on DBK17 and DBK18 is labeled J1 instead of JP1.
DBK Option Cards and Modules
886995
Signal Management 1-7