Teledyne PEM-9004 - Portable emissions analyzer - Manual (Page 21)

Portable Emissions Monitor Operational Theory
Teledyne Analytical Instruments 9
2.4.5 Calculating Undiluted CO Concentration
To calculate the uncompensated CO concentration the PEM-9004
uses the excess air as calculated above and the hydrogen compensated
value sensed by the CO electrochemical cell to arrive at an undiluted CO
concentration in ppm. The following equation is used:
Where: Lambda is the excess air as calculated above.
2.5 Sample System
The built-in sample system on the PEM-9004 can be though of as a
fully integrated data acquisition system. In addition to sampling the gas
stream and safely diverting a portion through the analyzer, it also gathers
data on pressure, temperature of the gas stream, and ambient
temperature.
The sample system is comprised of the following sections:
•
sample probe
•
sample and CO sensor protect pumps
•
gas conditioning section
•
temperature and pressure measurement
The probe is a steel tube connected to several feet of neoprene
tubing. It samples the exhaust gas stream and directs a portion into the
analyzer via the neoprene tubing. Integral with the sample probe are 2
type K (NiCr-Ni) thermocouples, one which measures the gas stream
temperature at the tip and the other sensing the air or ambient
temperature. A piezioresistive element is also contained within the probe
for converting pressure of the gas to an electronic signal used by the
microprocessor to determine the gas or draft pressure.
Waste gas is sampled through the probe and drawn into a filter
section in the analyzer by means of an 0.8 lpm pump through the Gas In
port on the front panel. Figure 2-4 shows the sample conditioning
section of the PEM-9004.
Lambda CO CO(0%)
Ч =