162 Theory of Operation 083730300A DCN8101
SAMPLE PRESSURE AND FLOW
These are analog signals from two sensors that measure the pressure and flow rate of the
gas stream at the outlet of the sample chamber. This information is used in two ways.
First, the sample pressure is used by the CPU to calculate CO concentration. Second, the
pressure and flow rate are monitored as a test function to assist the user in predicting and
troubleshooting failures.
6.4.5.3 THERMISTOR INTERFACE
This circuit provides excitation, termination and signal selection for several negative-
coefficient, thermistor temperature sensors located inside the analyzer. They are as
follows:
SAMPLE TEMPERATURE SENSOR
The source of this signal is a thermistor located inside the sample chamber of the Optical
Bench. It measures the temperature of the sample gas in the chamber. This data is used
to during the calculation of the CO concentration value.
BENCH TEMPERATURE SENSOR
This thermistor is attached to the sample chamber housing. It reports the current
temperature of the chamber housing to the CPU as part of the bench heater control loop.
WHEEL TEMPERATURE SENSOR
This thermistor is attached to the heatsink on the GFC Wheel motor assembly. It reports
the current temperature of the wheel/motor assembly to the CPU as part of the Wheel
Heater control loop.
BOX TEMPERATURE SENSOR
A thermistor is attached to the motherboard. It measures the analyzer’s internal
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 5.7.3).
6.4.5.4 ANALOG OUTPUTS
The analyzer comes equipped with four analog outputs: A1, A2, A3 and A4. The type of
data and electronic performance of these outputs are configurable by the user (see
Section 2.5.8).
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.
6.4.5.5 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 sync/demod
board that initiate the DARK CALIBRATION procedure.
To Next Page
Loading...