December 2001 Monitoring Functions 6 – 167
6.11.8 I
2
t Monitoring (Digital Axes Only)
The instantaneous motor current is limited to either the maximum current of
the power supply unit, or the maximum motor current, whichever is lower.
The values result from the type of power supply unit and type of motor, and
are saved in the motor or power-supply-unit table.
In addition, I
2
t is monitored:
For this purpose, the squares of the actual current values are integrated. For
feed motors, the duration of integration is 10 s, for main spindle motors 150 s.
The power module's rated current or the reference value for “I
2
t monitoring
of the motor” is used as the I
2
t limit value, whichever is smaller.
7
77
7 Enter a reference value for I
2
t monitoring for both
• MP2302.x for feed motors
• MP2303 for the spindle motor
The input value is a factor of the rated current of the motor (1 = rated current
of the motor).
If you enter zero, the I
2
t monitoring for the motor (not for the power supply
unit) is switched off.
If the mean current value from the integral exceeds the I
2
t limit value, the I
2
t
early warning signal responds.
I
2
t limit If the mean current value from the integral exceeds the 1.1-fold value of the
I
2
t limit value, the I
2
t limit responds. Within 0.4 s the motor current is throttled
to the 1.1-fold value of the I
2
t limit.
If the calculated mean current value falls below the 1.1-fold of the mean
current value, limiting is canceled.
MP2302.0-8 Reference value for I
2
t monitoring of feed motors
for axes 1 to 9
Input: 0 to 1000.000 [· rated current of motor]
0: I
2
t monitoring of feed motors switched off
1: Rated current of motor as reference value
MP2303 Reference value for I
2
t monitoring of spindle motor
Input: 0 to 1000.000 [· rated current of motor]
0: I
2
t monitoring of spindle motor switched off
1: Rated current of motor as reference value
Note
There is no I
2
t limitation for spindle drives.
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