General purpose low pass filter [II]

The latest firmware of the iPOS line of intelligent drives and iMOT line of intelligent motors has introduced a low pass filter that can be applied to any 16 bits variable.

The filter configuration is made by specifying the address of the variable that needs to be filtered and the filtering level. The corresponding parameters are VARFIL_ADR and VARFIL_CFG.

Remark: The filtering level (VARFIL_CFG) has valid values between 0 (total attenuation) and 32767 (no filtering at all).

The filter output can be read in the VARFIL_VAL variable.

Remark: By default this filter is configured for the motor current (IQ variable).

To better understand the benefits of this filter let's see how it works in case of the IQ variable.
First we need to mention that the IQ variable address is 0x0230. This can be checked using the Command Interpreter in EasyMotion Studio or EasySetUp.

As it is mentioned above the VARFIL_ADR parameter has to be set with the address of the variable that needs to be filtered. In this case, 0x0230. This example will show you how to do that - using the Command Interpreter we're writing the value 0x0230 into the VARFIL_ADR parameter.

Once the VARFIL_ADR parameter is set, we can check the filtration level (the VARFIL_CFG parameter value) and adjust it, if the case. For demo purpose we will set the filtration level to 1000.

Using the logger, we can record the unfiltered variable (IQ in this case) and the filtered variable (the filter output - VARFIL_VAL).

The VARFIL_CFG value can be changed until we get the needed results.
If the filtering value is decreased too much (thus increasing the attenuation), the phase shift and amplitude loss will be quite noticeable (see the picture below).

If the VARFIL_CFG parameter is set to 32767 there will be no filtering (see the picture below).

Remark: Beside this generic low pass filter that can be applied to any 16 bits TML variable, there's a similar one acting on the analog feedback input (AD2 variable), which can be configured using AD2FIL_CFG parameter (filtering power). Its output (the filtered analog feedback) can be found in the AD2FIL_VAL variable.