Before going into the problem, here is some hardware/software information:

Device accessed: Ohaus Scout Pro Digital Weight Machine (product link)
Interface used: USB (product link)
Serial Port: COM3
OS: WinXP
Python Version: Activestate Python 2.7
pyserial version: 2.5

Python recognized this serial port and had no problems opening it. I am new to python as well as pyserial. I couldn't figure out how exactly can I read data from the serial port. I used the following code:

import serial
ser=serial.Serial(port='COM3',timeout=3)
s=ser.read(100) #reading up to 100 bytes
print s

This prints nothing. During those 3 seconds timeout, I placed an object on the weighing machine and it showed 100grams on the weighing machine. But, this data is not showing on my computer. How can I read this data using pyserial?