After reading the in the PID Tips in the Visilogic helpfile I think we need to set the The HSO frequency value to 4.
In the helpfile is written:
If you use an SSR, you can use a Unitronics PLC that supports a high-speed output. In Hardware Configuration, set the Frequency (F=1/CT) parameter's Power-up Value to 5 to 10Hz ( which is 0.2 -0.1s cycle time). Link the PWM Duty Cycle MI to the CV. Note that in order to activate the output pulses, you must SET the RUN MB linked to the HSO in Hardware Configuration.