Influences on the measurement
Dust load
As long as the laser beam is able to generate a signal for the detector, the dust load of the process gases does not
influence the analytical result. By amplifying the signal automatically, measurements can be carried out without any
negative impact. The influence from high dust load is complex and is dependent on the optical path length (probe
length), particle size and particle size distribution. At longer path lengths the optical attenuation increases rapidly.
Smaller particles also have a significant impact on the optical attenuation: the smaller the particles are, the more dif-
ficult the measurement will be. For high dust load applications, please consult your local METTLER TOLEDO repre-
sentative.
Temperature
The temperature influence on an absorption line must be compensated for. An external temperature sensor can be
connected to the GPro 500. The signal is then used to correct the measurement results. Without temperature com-
pensation the measurement error caused by process gas temperature changes affects the measurement substan-
tially. Therefore, in most cases an external temperature signal is recommended.
Pressure
The process gas pressure affects the line shape of a molecular absorption line and influences the measurement
results. An external pressure sensor can be connected to the GPro 500. When the correct process gas pressure is
supplied, the GPro 500 uses a special algorithm to adapt the line shape and effectively compensate for the pressure
influence as well as the density effect. Without compensation the measurement error caused by process gas pres-
sure changes is substantial. Therefore, in most cases an external pressure signal is recommended.
Cross interference
Since the GPro 500 derives its signal from one or more fully-resolved molecular absorption lines, cross interference
from other gases is eliminated. The GPro 500 is therefore able to measure the desired gas component very selectively.
Note
Always take great care when choosing the measurement location. Positions where there are fewer particles, the tem-
perature is lower or there is a more suitable process pressure, are recommended. The more optimized the measure-
ment location is, the better the overall performance of the system will be. For advice on the optimal measurement
location, please contact your local METTLER TOLEDO representative.
Typical applications
Industry Safety Control Process Control
Chemical ••
Petrochemical ••
Refining ••
Power –•
Hazardous waste –•
Tank farms/Vapor recovery •–
Influences on the measurement/Typical applications GPro™ 500 TDL Series
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