Filtering factor - GMP251

GMP251 User Guide

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Modbus register 777 sets the CO2 filtering factor.

The filtering factor affects the speed at which the latest CO2 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 affect 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 effect 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 2-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:

o new = o old + ( m new o old ) × f

New output
Previous output
New measurement
Filtering factor