can any one tell me why the word precision is used in precision rectifier and what is the difference between precision rectifier and the normal rectifier... it`s urgent

 

A simple rectifier circuit uses a diode. The input voltage has to exceed the turn-on voltage (0.6V for ordinary Si diode) before rectification is achieved.

A precision rectifier is an active circuit using an opamp and a diode in the feedback loop. This overcomes the turn-on "knee" voltage.

 

To add to what MC said, this is useful for test equipment, where eliminating extra variables is required.

 

The op amp reduces the turn-on voltage of a diode in its feedback loop by a factor equal to the open-loop gain of the op amp. For practical op amp gains this reduces the forward voltage to a fraction of a mV, thus giving a "precision" or near ideal diode characteristic for the rectifier function.