The analogue output is controlled by Paramater P0771, here you will find 'in000' and 'in001'.
So parameter p0771, in000 should be set to 21 for output frequency.
This output is 0/20ma, available at terminals 12 & 13. If you need to have a Voltage output put a 500 Ohm, (470 Ohm is more readilly available), into terminals 12 and 13. This will provide 10 Volts proportional to frequency or speed, across the resistor.
At 50Hz you will have 10 Volts, 0 Hz 0 Volts.
I know this is not 24 Volts but as close as I can get........