speed feedback configuration

hi guys,
I want to know the difference between an encoder feedback configuration & voltage feedback configuration in a DC drive.

Does this selection have any bearing on the precision of motor control by the drive?

If the motor is gonna be shock loaded often, then it will be better suited to use an encoder or tach feedback. Voltage feedback can be utilized if the speed fluctuating a couple percent under load will not cause problems. Hope this helps.

The difference between the two is, encoder feedback uses an encoder to tell the drive the position of the rotor. The encoder is bolted to the motor shaft ODE.
Voltage feedback is a measurement of the counter emf to give a guesstimate of rotor position. This is all internal @ the drive.

One little correction and a comment. First, the encoder is not generally an absolute encoder so it's pulse stream only tells the rotational velocity of the shaft, not position. Second, a pulse encoder is accurate plus or minus one pulse where voltage feedback depends upon the accuracy and stability of the field current and is around 3-4% accurate on velocity. Also, you cannot use field weakening without an encoder or tachometer on the shaft.

the voltage is used for speed and the encoder for the position.
when you only have encoder you must have two positions and two times to calculate the speed.
the tacho is direct.

A DC(brushed) drive feedback only cares about velocity. It can infer velocity from voltage(back EMF), and as stated is not real accurate, but good enough for many applications. If an encoder is used, it is not going to be absolute or quadrature. It will just be a single channel pulse train that the drive interprets, very accurately, as velocity. A DC drive doesn't care about rotor position, since the commutation is all mechanical(brushes).