Model 360E Instruction Manual THEORY OF OPERATION
10.3.6.3. Thermistor Interface
This circuit provides excitation, termination and signal selection for several negative-coefficient, thermistor
temperature sensors located inside the analyzer. They are:
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 CO2
concentration value.
Bench Temperature Sensor
This thermistor, attached to the sample chamber housing, reports the current temperature of the chamber
housing to the CPU as part of the bench heater control loop.
Wheel Temperature Sensor
This thermistor (attached to the heat-sync on the GFC wheel motor assembly) 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 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).
10.3.6.4. 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 CO2 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 O2 sensor option is installed in the M360E. In this case, the
currently measured O2 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
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