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Model GFC7000E Instruction Manual THEORY OF OPERATION
04584 Rev A1 172
10.3.6.4. Analog Outputs
The analyzer comes equipped with four analog outputs: A1, A2, A3 and a fourth that is a spare.
A2 and A1 Output
The first two, A2 and A1 are normally set up to operate in parallel so that the same data can be
sent to two different recording devices. While the names imply that one should be used for
sending data to a chart recorder and the other for interfacing with a datalogger, either can be
used for both applications.
Both of these channels output a signal that is proportional to the CO
2
concentration of the sample
gas. The A1 and A2 outputs can be slaved together or set up to operated independently. A variety
of scaling factors are available, See Section 6.9.4 for information on setting the range type and
scaling factors for these output channels.
A3 Output
The third analog output, labeled A3 is special. It can be set by the user (see Section 6.9.9) to
carry the current signal level of any one of the parameters accessible through the A3 menu of the
unit’s software.
Spare Output
The fourth analog output, termed SPARE is not used in the MGFC7000E.
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: A2, A2 & A3.
Output Loop-back
All four analog outputs are connected back to the A/D converter through a Loop-back circuit. This
permits the voltage outputs to be calibrated by the CPU without need for any additional tools or
fixtures.
10.3.6.5. 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 ELECTRICAL TEST and DARK CALIBRATION procedures. Likewise, the synch/demod board
uses this interface to send the SYNC warning signal to the CPU (see Sections 6.9.5, 6.9.6 and
11.1.1).