Dynamic filter

The dynamic IIR filter automatically switches through the 8 different IIR filters depending on the weight change. The idea:

• The target state is always the IIR8-Filter, i.e. the greatest possible damping and hence a very calm measured value.
• In the input variable changes rapidly the filter is opened, i.e. switched to the next lower filter (if still possible). This gives the signal edge more weight and the measured value curve can follow the load quickly.
• If the measured value changes very little the filter is closed, i.e. switched to the next higher filter (if still possible). Hence the static state is mapped with a high accuracy.
• The evaluation as to whether a downward change of filter is required or whether an upward change is possible takes place continuously at fixed time intervals.

Parameterization takes place via the CoE entries 0x8000:13 and 0x8000:14. Evaluation takes place according to two parameters:

• The “Dynamic filter change time” object (0x8000:13) is used to set the time interval at which the existing signal is re-evaluated.
• Object 0x8000:14 is used to specify the maximum deviation that is permissible during this time without filter switching occurring.

Example:

The dynamic filter is to be adjusted in such a manner that a maximum slope of 0.5 digits per 100 ms (5 digits per second) is possible without the filter being opened. This results in a “calm” measured value. In the case of a faster change, however, it should be possible to immediately follow the load.

• Dynamic filter change time (0x8000:13) = 10 (equivalent to 100 ms)
• Dynamic filter delta (0x8000:14) = 0.5 (related to the calculated load value)

The measured value curve is shown below for a slower (left) and faster (right) change.

• Links: The scales are slowly loaded. The change in the weight (delta/time) remains below the mark of 0.5 digits per 100 ms. The filter therefore remains unchanged at the strongest level (IIR8), resulting in a low-fluctuation measured value.
• Right: The scales are suddenly loaded. The change in the weight immediately exceeds the limit value of 0.5 digits per 100 ms. The filter is opened every 100 ms by one level (IIR8 --> IIR7 --> IIR6 etc.) and the display value immediately follows the jump. After the removal of the weight the signal quickly falls again. If the change in the weight is less than 0.5 digit per 100 ms, the filter is set one level stronger every 100 ms until IIR8 is reached. The green line is intended to clarify the decreasing “noise level”