I believe this will depend on the accuracy of the RPM value You want.
Values converted inside the robot directly from the DIs will be under the influence of some constrains, like robot scan time and any other bottleneck tha can be presented by the system.
I feel like you won't be able to do it on the Kuka as I/O drivers are only good for refreshing every 4ms I believe. (I.e. i assume 24000 RPM is sufficiently fast that the 4ms signal updating on the KRC is not X2 for Nyquist sampling theorem)
I would buy a dedicated Tachometer module for what ever bus you're using.
Sorry, I'm pretty sure it only updates every 12ms, 4ms is for RSI. Even so, way too slow.
at 24000RPM and 3 pulse per revolution, you are looking at 72000 pulses per minute or 1200 pulses oer second (that is period of 0.833ms.
but due to 12ms interpolation time, this is clearly not going to work. you need something that can handle high speed. without resorting to external hardware, you can try connecting this to a one of inputs on fast measure interface of your controller. i am unsure of actual hardware specs but if i recall it was able to catch camera triggers much shorter than pulses your spindle is you are going to see (10uS?).
have not tried it myself but guess should be pretty simple, such as
DECL INT iSpindleRPM = 0 ;
INTERRUPT DECL 10 WHEN $TIMER[1]>1000 Do GetRPM()
INTERRUPT ON 10
$TIMER[1]=0
$TIMER_STOP[1]=FALSE
DEF GetRPM()
iSpindleRPM = $FAST_MEAS_COUNT[1]*20/$TIMER[1] ; 60/3=20
$TIMER[1]=0
$FAST_MEAS_COUNT_RESET = TRUE
$FAST_MEAS_COUNT_RESET = FALSE
END
