Help me design a RPM sensor that can be interfaced with PLC

[ayyub]

Hi guyz
I want RPM SENSOR guidence.I am actually working on Automation of Diesel Generator as my final year project.For that i am designing an ATS(Automatic Transfer Switch).In ATS when Main power goes off the ATS will transfer the Generator Output voltage on the load.The Output Voltage of Generator is only provided to the Load if the rated rpm is 1500(as i observed).
So i need rpm sensor that can be interfaced with PLC.The RPM sensor should have either analog or digital output so it will be easier to be interfaced with PLC .The Generator is showing RPM also but it is analog meter.
Guidence needed.

 

[kender]

rpm sensors

Here are some options for the RPM sensors:
- Hall effect. This is especially useful, when you have steel gears. Hall effect sensors are commonly used in cars for RPM sensing.
- Inductive (aka eddy current)
- Optical
- Capacitive

The choice would depend on mechanical aspects of your design. Is there a gear box? What are the gears made of? Can you put the sensor inside the gearbox?