Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 312)

Model 9110TH NOx Analyzer Principles of Operation
Teledyne Analytical Instruments 292
PMT TEMPERATURE: This signal is the output of the thermistor attached to the PMT
cold block amplified by the PMT temperature feedback circuit on the PMT preamp
board. It is digitized and sent to the CPU where it is used to calculate the current
temperature of the PMT.
This measurement is stored in the analyzer. Memory as the test function PMT TEMP
and is viewable as a test function (see Section 6.2.1) through the analyzer’s front panel.
NO
2
CONVERTER TEMPERATURE: This parameter is measured with a Type-K
thermocouple attached to the NO
2
converter heater and its analog signal is amplified by
the circuitry on the relay board. It is sent to the CPU and then digitized and is used to
calculate the current temperature of the NO
2
converter. It is also stored in the DAS and
reported as test function MOLY TEMP.
SAMPLE GAS PRESSURE: This is measured upstream of the reaction cell, stored in
the DAS and reported as SAMPLE. The vacuum gas pressure is measured downstream
of the reaction cell and is stored in the DAS and reported as RCEL. For more
information on these sensor’s functions see Section 8.3.10.
O
3
GAS FLOW This sensor measures the gas flow upstream of the ozone generator,
stored in the DAS and reported as test function OZONE FL. For more information on
this sensor’s function see Section 8.3.10.
8.5.9.3. Thermistor Interface
This circuit provides excitation, termination and signal selection for several negative-
coefficient, thermistor temperature sensors located inside the analyzer. They are:
REACTION CELL TEMPERATURE SENSOR: A thermistor embedded in the reaction
cell manifold. This temperature is used by the CPU to control the reaction cell heating
circuit and as a parameter in the temperature/pressure compensation algorithm. This
measurement is stored in the analyzer’s DAS and reported as test function
RCEL TEMP.
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 through the front panel display.
It is also used as part of the NO, NO
X
and NO
2
calculations when the instrument’s
Temperature/Pressure Compensation feature is enabled. This measurement is stored in
the analyzer. Memory as the test function BOX TEMP and is viewable as a test
function (Section 4.2.1) through the analyzer’s front panel.
The thermistor inside the PMT cold block as well as the thermistor located on the
preamplifier board are both converted to analog signals on the preamplifier board before
being sent to the motherboard’s A/D converter.
O
2
SENSOR TEMPERATURE: For instruments with the oxygen sensor option
installed, the thermistor measuring the temperature of the heating block mounted to the
sensor is reported as test function O2 TEMP on the front panel. This temperature is
maintained at 50° C.