Teledyne 9110E - Nitrogen Oxides Analyzer - Manual (Page 198)

Theory of Operation Model 9110E Instruction Manual
184 M9110E Rev B
• The NO
2
converter temperature 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 iDAS and reported
as test function MOLY TEMP.
• The sample gas pressure is measured upstream of the reaction cell, stored in the
iDAS and reported as SAMPLE. The vacuum gas pressure is measured downstream
of the reaction cell and is stored in the iDAS and reported as RCEL. For more
information on these sensor’s functions see Section 10.2.10.
• The O
3
gas flow is measured upstream of the ozone generator, stored in the iDAS
and reported as test function OZONE FL. For more information on this sensor’s
function see Section 10.2.10.
10.3.5.3. Thermistor Interface
This circuit provides excitation, termination and signal selection for several negative-
coefficient, thermistor temperature sensors located inside the analyzer. They are:
• 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.
This measurement is stored in the analyzer’s iDAS 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 6.2.1) through the analyzer’s front panel.
• The IZS option’s thermistor is attached to the IZS oven and reports the current
temperature of the NO
2
permeation source to the CPU as part of a control loop that
keeps the tube at a constant temperature. It is stored and reported as test function
IZS TEMP.
• 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. They are not connected to the
motherboard’s thermistor circuitry. The cold block temperature is stored and
reported as test function PMT TEMP, whereas the preamplifier board temperature is
neither stored nor reported. It is used only as a reference internal to the
preamplifier.
10.3.5.4. Analog Outputs
The analyzer comes equipped with four analog outputs. On the instrument’s rear panel
ANALOG connector, they are labeled A1, A2, A3 and A4.
Outputs labeled A1, A2 and A3 carry the concentration signals of NO
X
, NO and NO
2
,
respectively. A variety of scaling measurement and electronic factors apply to these signals.
See Section 6.6 for information on setting the reporting range type and measurement range
scaling factors for these output channels. See Sections 6.7 for instructions on setting the
electronic scaling factors for these channels.