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5.1.1 Mechanical time constant
The
mechanical time constant 811 is the time which the drive needs to accelerate
from a standstill to rated speed with rated current.
Neglecting the friction,
dt
dω
JT ⋅=
T is the rated torque of the machine, J the entire mass moment of inertia of the drive.
T
dω
Jdt ⋅=
ωπ2
60
n
=⋅⋅
n is the no load speed of the machine, thus resulting in the mechanical time constant
t
m
:
60T
π2nJ
t
m
⋅
⋅⋅⋅
=
If the entire mass moment of inertia J is not exactly known, the mechanical time con-
stant t
m
can also be determined by an acceleration test.
For this, the plant constant
Turns per meter 812 must be set first. After this, the lift-
in
g application is to be run without load at a constant speed (half rated speed of the
machine) (clockwise, lifting).
The actual value
Load 242 is noted.
Now, the lifting application is accelerated from standstill with the
Acceleration (clock-
wise)
420 required in operation to a speed above the rated speed of the machine
(clockwise, lifting). Now, the actual value
Estimated load 243 is evaluated.
If the value displayed for the estimated load is larger than the figure established be-
fore, the parameter value
mechanical time constant 811 must be increased. In the
opposite case, this figure must be reduced.
Parameter Setting
No. Description Min. Max. Fact. sett.
811 Mech. time constant 0.000 s 65.000 s 0.190 s
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