Dear Mr.Dino
Yes, It is possible to count the frequency and send it to the analog output. What you have to do is take the input in MFD Titan or Easy 800 input 1/2/3/4(any one input) and configure this input to CF (frequency counter) function block. This function block will count the no. of pulse/second. If you know the volume of water /pulse you can take this CF output to LS function block and scale it to represent flow rate in gpm/lpm/m3/hr. Once you have this, take this LS output to analogue output via PID function block. You may use proportional only or Proportional plus integral for controlling the analog output value which inturn will control VFD of the pump motor.
I hope my suggestion is useful
Regards
K.Vedaraman