Vaisala GMP252 - Filtering Factor; A.4 Filtering Factor

A.4 Filtering Factor
Modbus register 777 sets the CO
2
filtering factor.
The filtering factor aects the speed at which the latest CO
2
measurement is integrated into
the output of the probe. A new measurement is produced approximately every two seconds.
By default, the filtering factor is set to 1.0, which means the latest measurement is shown
directly in the output, without any filtering. If the measuring environment produces
occasional exceptionally high or low readings that need to be averaged out in the output,
filtering can be applied.
To apply filtering, you need to set a filtering factor that determines how much the previous
measurements aect the calculation of measurement output. For example, when using
filtering factor of 0.1, the new output is a combination of previous measurements (90 %) and
the latest measurement (10 %).
Examples of the eect of filtering on output:
• Filtering factor 1.0 = No filtering, the latest measurement is output directly without
integrating previous measurements.
• Filtering factor 0.5 = The reading output shows ~75 % of the measurement change after
two two-second measurement cycles and ~93 % after four cycles.
• Filtering factor 0.1 = The reading output shows ~90 % of the measurement change after
22 measurement cycles.
The
configuration range of the filtering factor is 0 ... 100 in the 16-bit register: for example, to
set the factor to 0.5, set the value of the register to 50.
The following formula is used when calculating the output:

new
= 
old
+ 
new
 
old
× 
o
new
New output
o
old
Previous output
m
new
New measurement
f Filtering factor
GMP252 User Guide M211897EN-D
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