I*t calculation in the AX5000 servo drive
 | Reference variables for the I*t calculation: P-0-0052; P-0-0090; P-0-0091; P-0-0092; P-0-0093 |
The I*t calculation serves as a protective function for the output stage of the AX5000 servo drive. The max. permissible overcurrent time area (I*tmax ) depends on the size of the devices. The servo drive can supply the peak current for the time tmax. The value is then limited to the nominal current on expiry of tmax.
In earlier firmware revisions the max. permissible overcurrent time area could not be used fully. From firmware v2.06 (build 18) the complete overcurrent time area of the servo drive is now available.
The overcurrent time area of the servo drive depends on the peak and nominal current of the different device sizes:
If the demanded overcurrent is smaller than the peak current, it can be supplied for a longer time. The possible time tAppl can be calculated as follows:
The calculation is influenced by the following parameters:
Number | Name | Note |
|---|---|---|
P-0-0052 | Time limitation for peak current | = 0 for max. utilization of the I*t area |
P-0-0090 | Channel peak current | Dependent on the size |
P-0-0091 | Channel rated current | Dependent on the size |
P-0-0092 | Configured channel peak current | Dependent on the application |
P-0-0093 | Configured channel rated current | Dependent on the application |
S-0-0112 | Amplifier rated current | Dependent on the size |
tmax | Max. time for Ipeak | device-related 3 s1) or 7 s2) |
1): 3 s for servo drives > AX5140 (see electrical data in the AX5000 system manual)
2): 7 s for servo drives from the AX52xx and AX5101 – AX5140 series.
On changing status from Pre-Op to Op, the firmware in the AX5000 checks whether the value set in parameter P-0-0052 is permissible. A parameter error appears if the value is impermissible.
With the inserted parameters, the equation mentioned above looks like this:
The current is limited to the value of P-0-0091 on expiry of the time tAppl.
Meaning of the parameter P-0-0052:
P-0-0052 should generally be set to 0 so that the AX5000 supplies the overcurrent for the maximum possible time.
For reasons of compatibility, the default value is not zero, but 3000 ms. Two cases must be distinguished when setting P-0-0052:
1) P-0-0052 = 0
The current IAppl is always supplied for the max. possible time (max. 1000 s).
2) 0 < P-0-0052 ≤ P-0-0052max (compatibility mode)
A current in the magnitude of the parameter P-0-0092 is limited after the set time
(P-0-0052 = 1 ms…65535 ms) to the value of the parameter P-0-0093.
With IAppl < P-0-0092, tAppl is > P-0-0052.