When you say "HSC", do you mean that you are using a 1756-HSC module ?
One of the operating modes of the 1756-HSC is "Rate" mode, whose default values typically give you pulses per second. The User Manual and RA Knowledgebase should include enough information for you to set that up.
The pulses per second of the flowmeter and the K-factor will tell you how many cubic meters of fluid per second are flowing through the pipe, so you need to know some of the parameters of the pump to know how fast it's turning.
What sort of pump is it ? Do you have any information about how many cubic meters per second it pumps at a given RPM ?