Principles of Operation
Teledyne API - Model T200H/T200M Operation Manual
290
8.5.1.2. Flash Chip
This non-volatile, embedded flash chip includes 2 MB of storage for calibration data as
well as a backup of the analyzer configuration. Storing these key data on a less heavily
accessed chip significantly decreases the chance of data corruption.
In the unlikely event that the flash chip should fail, the analyzer will continue to operate
with just the DOM. However, all configuration information will be lost, requiring the
unit to be recalibrated.
8.5.2. SENSOR MODULE, REACTION CELL
Electronically, the T200H/M sensor assembly (see Figure 3-5) consists of several
subassemblies with different tasks: to detect the intensity of the light from the
chemiluminescence reaction between NO and O
3
in the reaction cell, to produce a current
signal proportional to the intensity of the chemiluminescence, to control the temperature
of the PMT to ensure the accuracy and stability of the measurements and to drive the high
voltage power supply that is needed for the PMT. The individual functions are described
individually below, Section 7.6.5 shows the sensor assembly and its components.
8.5.2.1. Reaction Cell Heating Circuit
The stability of the chemiluminescence reaction between NO and O
3
can be affected by
changes in the temperature and pressure of the O
3
and sample gases in the reaction cell.
In order to reduce temperature effects, the reaction cell is maintained at a constant 50
°
C,
just above the high end of the instrument’s operation temperature range.
Two AC heaters, one embedded into the bottom of the reaction cell, the other embedded
directly above the chamber’s exhaust fitting, provide the heat source. These heaters
operate off of the instrument’s main AC power and are controlled by the CPU through a
power relay on the relay board (Section 8.5.7). A thermistor, also embedded in the
bottom of the reaction cell, reports the cell’s temperature to the CPU through the
thermistor interface circuitry of the motherboard (Section 8.5.9.3).
07270D DCN7141