as the output in pulse form and limited to 752 pulses for one litter of liquid flow, which technique could be used to calculate the real time flow of the said liquid from the sensor.
(note : the sensor works on IR detection)

Some of this may be in other readable posts, I just type all I can think of from my flowmeter experience.

1) use a schmitt trigger somewhere in the input
2) you may need to use the "dual method" for flow rate.
a) for high flow: pulses per second
b) for low flow: time for a pulse (note rising edge to rising edge or falling edge to falling edge the pulses are never symmetrical)
3) make a power down detect that saves the volume in nvm (or use FRAM/BatteryBacked NVM and do it regularily) It is embarrising not to know how much is in the tank after a power failure.

NOTE: flowmeters are usually in very noisy environments, I once had to amplify and shape the signal at the flowmeter. You may have to. The best is if you can get differential transmission of the pulses.

If you also have to control volume (close the valve after n liters) you MUST adhere to the FAQ on noise.

Erik