Question:
What has to be considered when using the touch probe interfaces, when the assigned speed (phase difference signal) is pre-scaled, e. g. by means of a converter block?
Answer:
When touch probe signals are used, three system signals must always be used in the POU:
the phase difference value (e. g. system variables DFIN_nIn_v, MCTRL_nNAct_v)
the status bit via detection of a touch probe signal (e. g. system variables DFIN_bTPReceived_b, MCTRL_bActTPReceived_b)
the last scan value indicating the number of increments, that have been detected between touch probe event and POU start (e. g. system variables DFIN_dnIncLastScan_p, MCTRL_dnActIncLastScan)
If the phase difference signal is pre-scaled (like the master frequency signal DFIN_nIn_v via the function block L_CONVX1 in the example below), the assigned last scan value has also to be scaled in the same relation (like the system variable DFIN_dnIncLastScan_p that is scaled by the function block L_CONVPP1, see example below).If the system variables for the phase difference signal and last scan value are pre-scaled differently, the control in the touch probe-evaluating function block will be correspondingly inaccurate.
Applications:
Master encoders with numbers of pulses per revolution that cannot be set directly in C0425/000 and have to be scaled via a converter block connected in series.
All applications where phase difference signals first have to be converted before the touch probe is evaluated.
