Teledyne API Model 200AH NOX Analyzer Instruction Manual, 06492, Rev. G2
5-16
5.2.2.5. NO, NOX and O2 Cal Concentration
Before the M200AH can be spanned, it is necessary to enter the expected span concentrations for
NO and NOX. In single range mode there is one value each for the NO, NOX and O2 expected
span values. The span values are entered by pressing CAL-CONC-NO or CAL-CONC-NOX or
CAL-O2-CONC keys for NO , NOX and O2 span concentrations respectively.
If AutoRange is enabled, there is a different slope and offset for each of the 2 ranges for a total
of 4 expected span concentrations. Therefore there will be 2 span concentrations for NO and 2
span values for NOX. When AutoRange is enabled, the path to the expected span concentrations
contain an extra step. For the LOW concentration range the path is CAL-LOW-CONC-NO for
NO, and CAL-LOW-CONC-NOX for NOX. For the HIGH concentration range the pathways are
CAL-HIGH-CONC-NO and CAL-HIGH-CONC- NOX. These values must be entered to
correctly calibrate the instrument.
5.2.2.6. Formula Values
The slope and offset terms should be checked after each calibration. The values for these terms
contain valuable information about internal health of the analyzer. The range of acceptable
values and their meanings is given in Section 7.10.
To compute the NOX and NO or O2 concentrations, the formula for a straight line is used.
Where:
y = the NOx or NO or O2 concentration
m = the slope
x = the conditioned sensor output
b = the offset
y = mx + b
In comparison with analog analyzers the slope term is equivalent to the "span pot" and the b term
is equivalent to the "zero pot". Again, like an analog analyzer there is only a limited range of
adjustment allowed for either term, and there are consequences of having the values near the
high or low limits of their respective adjustment ranges.
The (x) term is the conditioned PMT signal. PMT signal is adjusted for current zero, AutoZero
value, range, temperature, and pressure.
The offset (b) term is the total background light. Therefore in the case of the NO channel the b
term should be very close to zero. The (b) for the NOX channel is often slightly higher than the
term for the NO channel. The extra background is mostly from the converter. The (b) term
incorporates the PMT reading, the AutoZero value, the current span value, temperature and
pressure compensation factors.