Jetter JetMove D203, User Manual

Page: 44 / 142

5 Technical Data
44 Jetter AG
5.2.2 I²t calculation
The digital servo amplifier JetMove D203 calculates the model of motor power loss
by an I²t calculation. The calculated value is a measure of the average power loss of
the motor. It is calculated in percent of the maximum motor power loss.
For this calculation it is important, that the parameters are entered correctly:
– Nominal current (which is the minimum of nominal motor current and nominal
servo amplifier current),
– Overload factor
– and time constant of the motor
The I²t calculation must be activated by JetSym or by the PLC program.
It is possible to parameterize the warning level.
The error level (error 30) is set to 100 %.
The I²t value is readable in a variable of JetMove D203 through JetSym or the PLC.
The digital servo amplifier JetMove D203 calculates the percentage of motor power
loss according to the following formula:
The formula shows that the 100 % value will never be reached as long as the average
motor current is lower than the nominal current of the motor.
Further, calculating always starts by 0 (at t = 0, the result of the equation is 0). After
some time that is by far longer than the motor time constant, the result does virtually
not change any more.
The time till error stop (x = 100 %) is a result of the following formula:
After reset, the values of the important parameters are:
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.
x(t) = Displayed value of the motor power loss in %
t = Time since start of motor running it with the average current (in seconds)
T = Motor time constant (in seconds)
Nominal current: 3 A
Overload factor: 2
Motor time constant: 1,800 s (30 min.)
x t
( )
100%
average motor current
rated current
-----------------------------------------------------
 
 
2
×
1 e
t
T
--- –
–
 
 
 
× =
t T 1
rated current
average motor current
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 
 
2
–
ln
× – =