Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 227)

Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 209
Box Temperature Sensor
A thermistor is attached to the motherboard. It measures the analyzer’s inside temperature. This
information is stored by the CPU and can be viewed by the user for troubleshooting purposes via the front
panel display (See Section 11.1.2).
9.3.6.4. Analog Outputs
The analyzer comes equipped with four analog outputs: A1, A2, A3 and A4. . 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.
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 data logger, 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 6.13.4 for information on setting the range type and scaling factors for
these output channels.
A3 Output
Analog output channel A3 is only active when the O
2
sensor option is installed in the GFC 7000TA. In this
case, the currently measured O
2
concentration is output.
Test Function Output
The fourth analog output, labeled A4 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 SETUP  MORE  DIAG 
TEST CHAN OUTPUT
submenu (See Section 6.13.9) of the unit’s software.
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.
9.3.6.5. 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).