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5 Technical Data
For this calculation it is important for the parameters
– nominal current (which is the minimum of nominal motor current and nominal
– overload factor
– and time constant of the motor
are programmed in correctly.
The I²t evaluation must be activated via JetSym or via the PLC program.
It is possible to parameterise the warning level. The error level (error 30) is set to
100%.
The I²t value is readable in a variable of JetMove 203-230 through JetSym or the
PLC.
The servo amplifier JetMove 203-230 calculates the percentage of the motor load
according to the following formula:
x t ( )
x(t) = Displayed value of the motor load in %
t = Time since start of the motor by this continuous current (in seconds)
T = Motor time constant (in seconds)
The formula shows that the 100% value will never be reached as long as the average
motor current is not greater than the continuous rated current of the motor.
Further the calculated value always starts with value 0 (with (t = 0) the result of the
equation is zero) and its change practically approaches zero for a time much higher
than the motor time constant.
The time until deactivating the motor (x = 100 %) is a result of the following formula:
t
After activating, the values for the significant parameters to be entered are the
following:
Continuous rated current:
Overload factor:
Motor time constant: 1800 s (30 min.)
With these parameters the 100 % error level will be reached if, for example the motor
is run by a current of 6 A for about 8 minutes and 30 seconds.
Important
40
servo amplifier current).
average motor current
×
---------------------------------------------------- -
=
100%
rated current
rated current
×
---------------------------------------------------- -
=
–
T
ln
1
–
average motor current
2
As, after activating, the I²t calculation always starts with value zero, the motor
load can only be calculated correctly, if, at activating the servo amplifier JetMove
203-230 (i.e. it has been connected to the 24 V logic power supply and
parametering the I²t function has been completed) is cold.
t
–
-- -
2
T
×
1 e
–
2
3 A
JetWeb
Jetter AG
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