Teledyne T803 12.6.4. HEATER CONTROL

Teledyne API T803 CO2/O2 Analyzer Operation Manual Principles of Operation
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D6
(
Y
ellow
)
O
2
Sensor Heater
D5
(
Y
ellow
)
–
CO2 Sensor
D1 (RED)
Watchdog Indicator
Figure 12-11: Status LED Locations – Relay PCA
12.6.3.2. WATCHDOG CIRCUITRY
The most important of the status LEDs on the relay board is the red I2C Bus
watch-dog LED. It is controlled directly by the analyzer’s CPU over the I2C Bus.
Special circuitry on the relay PCA watches the status of D1. Should this LED
ever stay ON or OFF for 30 seconds, indicating that the CPU or I2C bus has
stopped functioning, this Watchdog Circuit automatically shuts off all heaters.
12.6.4. HEATER CONTROL
12.6.4.1. TEMPERATURE CONTROL
At low magnetic field strengths levels, paramagnetic molecules follow Curie's
law to good approximation, which indicates that the susceptibility of
paramagnetic materials is inversely proportional to their temperature.
To minimize the effects of temperature variations on the O2 concentration
measurement the parametric sensor is raised to a high temperature level, 50C. A
cartridge heater implanted into the sensor is the heat source. The temperature of
the sensor is measured by a thermistor also inserted into the sensor body.
07276B DCN6418