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Model 9110T NOx Analyzer Principles of Operation
Teledyne Analytical Instruments 342
PMT TEMPERATURE: The PMT temperature is measured with a thermistor inside the PMT cold
block. Its signal is amplified by the PMT temperature feedback circuit on the preamplifier board and is
digitized and sent to the CPU where it is used to calculate the current temperature of the PMT.
The value of this signal is viewable via the front panel test function PMT TEMP and the SIGNAL I/O
function PMT_TEMP.
It is recorded by the DAS system as the parameter PMTTMP.
SAMPLE GAS PRESSURE SENSOR: This sensor, located on the flow/pressure sensor PCA,
measures the gas pressure in the sample chamber upstream of the sample gas stream flow control
assembly. Its functions are described in Section 13.2.4.1.
The value of this signal is viewable via the front panel test function SAMP and the SIGNAL I/O
function SAMPLE_PRESSURE.
It is recorded by the DAS system as the parameter SMPPRS.
VACUUM PRESSURE SENSOR: This sensor, also located on the flow/pressure sensor PCA, is
pneumatically located downstream from the reaction cell and measures the pressure of the gas mixture
inside the reaction cell . Its functions are described in Section 13.2.4.2.
The value of this signal is viewable via the front panel test function RCEL and the SIGNAL I/O
function RCEL_PRESSURE.
It is recorded by the DAS system as the parameter RCPRES.
O
3
FLOW SENSOR: This sensor, located on the flow/pressure sensor PCA, measures the flow rate of
the O
3
gas stream as it is supplied to the reaction cell. Its functions are described in Section 13.2.4.4.
The value of this signal is viewable via the front panel test function OZONE FLOW and the SIGNAL
I/O function OZONE_FLOW.
It is recorded by the DAS system as the parameter O3FLOW.
13.3.3.3. 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: The reaction cell temperature sensor is 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.
The value of this signal is viewable via the front panel test function RCEL TEMP and the SIGNAL
I/O function RCELL_TEMP.
It is recorded by the DAS system as the parameter RCTEMP.
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.
The value of this signal is viewable via the front panel test function BOX TEMP and the SIGNAL I/O
function BOX_TEMP.
It is recorded by the DAS system as the parameter BOXTMP.