Tachometer EC Fan


I want to read the rpm s from a EC (Electronically Commutated) fan.
I did it with a python script but I was wondering the best way to do it in NodeRed.
I don t realise how to get the pulses for minute using the raspberry nodes... My plan is to control 4 fan with one raspberry.
The tachometer info says : Tach output: open collector, 1 pulse per revolution, electrically isolated.

Thank you and happy new year everybody!