Elmo SERVO AMPLIFIER DBP SERIES User Manual

Page 20

DBP - Rev 6/93

This function should be activated whenever the rated current AND the peak

current of the motor are less than 20% of the amplifier rated continuous and

peak limits respectively.

Sometimes, oscillations may occur in the current loop due to the fact that

the feedback gain was multiplied. This can be resolved by substituting R4 with

a lower value.

4.3 Digital current limits

The servo amplifier can operate in the following voltage-current plane:

-Ip

-Ic

Intermittent

zone

Continuous

zone

-V

Ic - Continuous current Ip - Peak current

Fig. 4.1: Voltage-Current plane

Each amplifier is factory adjusted to have this shape of voltage-current

operating area with rated values of continuous and peak current limits. By

using the command CL(n) for the continuous and PL(n) for the peak it is

possible to adjust the current limits (continuous and peak independently) from

the rated values down to 10% of the rated values.

4.3.1 Time dependent peak current limit

The peak current duration is a programmable parameter which is also a

function of the peak amplitude and the motor operating current before the peak

demand. The user defines the maximum duration of the full amplitude peak by the

instruction PDn - n cannot be more than 2 seconds. In addition to this

definition, a digital filter is employed to ensure that the RMS value of the

current will not exceed the continuous current limit. The duration of Ip is

given by: