Model 300E Carbon Monoxide Analyzer
Instruction Manual
THEORY OF OPERATION
P/N 04288 Rev: A
177
Both of these channels output a signal that is proportional to the CO concentration
of the Sample Gas. The DAS and REC outputs can be slaved together or set up to
operated independently. A variety of scaling factors are available, See Section 7.5
for information on setting the range type and scaling factors for these output
channels.
Test Output: The third analog output, labeled TEST is special. It can be set by the
user (see Section 7.5.7) to carry the current signal level of any one of the
parameters accessible through the
TEST
menu of the unit’s software.
Spare Output: The fourth analog output, termed SPARE is not used in the M300E.
In its standard configuration, the Analyzer comes with all four of these channels set
up to output a DC voltage. However, 4-20mA current loop drivers can be
purchased for the first three of these outputs, REC, DAC, TEST.
Output Loopback: All four analog outputs are connected back to the A/D converter
through a Loopback circuit. This permits the voltage outputs to be calibrated by
the CPU without need for any additional tools or fixtures.
Internal Digital I/O
This channel is used to communicate digital status and control signals about the
operation of key components of the Optical Bench. The CPU sends signals to the
Synch/Demod Board that initiate the
Dark Calibration
and
Electrical Test
procedures. Likewise, the Synch/Demod Board uses this interface to send the
SYNC
warning signal to the CPU (see Sections 6.6.4, 6.6.5 and 11.1.1).
External Digital I/O
This External Digital I/O performs two functions.
STATUS OUTPUTS: Logic-Level voltages are output through an optically isolated
8-pin connector located on the rear panel of the analyzer. These outputs convey
good/bad and on/off information about certain analyzer conditions. They can be
used to interface with certain types of programmable devices (see Section 6.7.1).
CONTROL INPUTS: By ap5VDC power supplied from an external source
such as a PLC or Datalogger (see Section 6.7.2), Zero and Span calibrations can be
initiated by contact closures on the rear panel.