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Model 9110T NOx Analyzer Principles of Operation
Teledyne Analytical Instruments 343
INTERNAL SPAN GAS GENERATOR OVEN TEMPERATURE: This thermistor reports the
temperature of the optional internal span gas generator’s NO
2
permeation source to the CPU as part of a
control loop that keeps the tube at a high constant temperature (necessary to ensure that the permeation
rate of NO
2
is constant). It is stored and reported as test function IZS TEMP.
The value of this signal is viewable via the front panel test function IZS TEMP and the SIGNAL I/O
function IZS_TEMP.
It is recorded by the DAS system as the parameter IZTEMP.
Note There are two thermistors that monitor the temperature of the PMT
assembly:
One is embedded in the cold block of the PMT’s TEC. Its signal is
conditioned by the PMT preamplifier PCA and reported to the CPU via
the motherboard (see Section 13.3.3.2).
The second is located on the PMT Preamplifier PCA and is used only
as a reference for the preamplifier circuitry. Its output is neither
reported nor stored.
13.3.3.4. Analog Outputs
The analyzer comes equipped with four analog outputs. On the instrument’s rear panel analog connector
(see Figure 3-4), they are labeled A1, A2, A3 and A4.
CONCENTRATION OUTPUTS: 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 Sections 3.3.1.3 and 5.4 for information on setting the reporting range type and measurement
range scaling factors for these output channels.
See Sections 5.9.3.2 for instructions calibrating and scaling the electronic output of these channels.
TEST OUTPUT: The fourth analog output, labeled A4 is special. It can be set by the user (see Section
5.9.4) to carry the current signal level of most of the parameters accessible through the TEST menu of
the unit’s software.
In its standard configuration, the 9110T comes with all four of these channels set up to output a DC
voltage. However, 4-20mA current loop drivers can be purchased for the first three of these outputs,
A1, A2 and A3.
OUTPUT LOOP-BACK: All of the functioning analog outputs are connected back to the A/D
converter through a Loop-back circuit. This permits the voltage outputs to be calibrated by the CPU
without need for any additional tools or fixtures (see Section 5.9.3.4).
13.3.3.5. External Digital I/O
This external digital I/O performs two functions.
STATUS OUTPUTS: Logic-Level voltages (0-5 VDC) are output through an optically isolated 8-pin
connector located on the rear panel of the analyzer (see Figure 3-4). These outputs convey good/bad and
on/off information about certain analyzer conditions. They can be used to interface with certain types of
programmable devices.