E8500 Instruction & Operations Manual
version 1.017
Page 21 of 49
Unlike the other toxic sensors the carbon monoxide sensor is mounted in an assembly
that includes a three way electronic valve and an additional oxygen (dilution) sensor.
The sensor itself has an inboard filter to remove interference from NO gas.
This sensor has four electrodes. One measures the concentration of carbon monoxide
gas and the other the concentration of any interfering hydrogen gas (It is hydrogen
compensated).
Furthermore, this sensor assembly is designed to provide the CO sensor with a dual
range capability and also to purge the sensor with air, if the CO gas concentration
exceeds the sensor’s diluted upper limit.
If the CO concentration exceeds the sensor’s low range selectable upper limit, a
“dilution” pump turns on mixing dilution air with the sample. A second “dilution” oxygen
sensor measures the resultant concentration of the combined sample and air streams
and computes the correct CO concentration.
(For still higher CO concentrations please refer to the NDIR CO sensor option).
2. NDIR (INFRARED) SENSORS
The Model 8500 Plus emissions analyzer can be equipped with non-dispersive infrared
sensor (NDIR) measurement capability for the measurement of three gases: carbon
monoxide (high range), carbon dioxide and hydrocarbons.
The NDIR bench is designed for operation with combustion flue gas measurements and
also engine exhaust gases, according to the California BAR 97 regulations.
The infrared option has the following specifications:
GAS
RANGE
ACCURACY
CARBON MONOXIDE
(CO)
0% - 10%
10% - 15%
3% relative
5% relative
CARBON DIOXIDE
(CO
2
)
0% - 20%
20% - 50%
3% relative
5% relative
HYDROCARBONS
(HC or CxHy)
0 - 0.40 %
0.40 – 1.00 %
1.00 – 3.00 %
3% of Rdg. + 0.01%
5% of Rdg.
8% of Rdg.
