[SOLVED] [help] using XR4151 frequency to voltage converter

hi,

first here is an explanation of what i'm trying to do:

i need to measure the speed of a dc motor, to do so i used a photo diode, laser and frequency to voltage converter, on the disc of the motor i placed a duck tape to block the contact of the light from the photo diode, in the output of the photo diode i measured a pulses with a frequency.

i know the speed of the motor in the form of rad/sec

but i need to show that the speed measured by the XR4151 is the same as the given speed in the form of rad/sec

here is my data
speed(rad/sec) Vout(mV)[from the XR4151]
0 0
14 2
52 10
94 17.6
135 26.1
177 34.2
219 42.3


so far what i thought i needed to do
from the datasheet of the XR4151 i can see the relation between the vout and the input frequency to the XR4151
Vo=Fi/0.486
from there i can find the Fi (input frequency to the XR4151) [Hz=1/sec] one round per second
but i need to compare this with the speed [rad/sec]


maybe i do something wrong but i don't understand it yet.
please help me with this.

1Hz = 1rev/sec = 360deg/sec = 2*pi rad/sec = 6.28 rad/sec