Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 185)

Calibration Procedures Model 9110TH NOx Analyzer
Teledyne Analytical Instruments 165
5. CALIBRATION PROCEDURES
This section describes calibration procedures for the 9110TH/M. All of the methods
described here can be initiated and controlled through the front panel or the COM ports.
Interferents should be considered prior to calibration.
5.1.1. INTERFERENTS FOR NO
X
MEASUREMENTS
The chemiluminescence method for detecting NO
X
is subject to interference from a
number of sources including water vapor (H
2
O), ammonia (NH
3
), sulfur dioxide (SO
2
)
and carbon dioxide (CO
2
) but the Model 9110TH/M has been designed to reject most of
these interferents. Section 8.2.4 contains more detailed information on interferents.
Ammonia is the most common interferent, which is converted to NO in the analyzer’s
NO
2
converter and creates a NO
X
signal artifact. If the Model 9110TH/M is installed in
an environment with high ammonia, steps should be taken to remove the interferent
from the sample gas before it enters the reaction cell. TAI offers a sample gas
conditioning option to remove ammonia and water vapor (contact Sales).
Carbon dioxide diminishes the NO
X
signal when present in high concentrations. If the
analyzer is used in an application with excess CO
2
, contact TAI Technical Support for
possible solutions. Excess water vapor can be removed with one of the dryer options
described in Section 1.4. In ambient air applications, SO
2
interference is usually
negligible.
5.1.1.1. Conditioners for High Moisture Sample Gas
Several permeation devices using Nafion ® permeation gas exchange tubes are available
for applications with high moisture and/or moderate levels of NH
3
in the sample gas.
This type of sample conditioner is part of the standard 9110TH/M equipment to remove
H
2
O and NH
3
from the ozone generator supply gas stream but can be purchased for the
sample gas stream as well. All gas conditioners remove water vapor to a dew point of
about –20° C (~600 ppm H
2
O) and effectively remove concentrations of ammonia up to
about 1 ppm. More information about these dryers and their performance is available at
http://www.permapure.com/.
It is MANDATORY that for calibrations and operation to be valid, the analyzer be
calibrated using the same background gas (or dilutent) for zero and span, as the
background gas in the sample stream. Any other combinations will lead to calibration or
operational errors since the efficiency of the analyzer’s chemluminescent reaction varies
with the background gas, since the background gas acts as a quencher.
Note CALIBRATION vs. CALIBRATION CHECK:
DO NOT press the ENTR button during the following procedures if you are
performing only a calibration check. ENTR recalculates the stored values
for OFFSET and SLOPE, altering the instrument’s calibration.