Jetter JM-108, Руководство пользователя

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5 Technical Specifications
38 Jetter AG
5.2 Motor Protection
5.2.1 I²t Calculation
The digital servo amplifierJetMove 108 calculates the model of motor power
dissipation by an I²t calculation. The calculated value is a measure of the average
power dissipation of the motor. It is calculated in percent of the maximum motor
power dissipation.
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 has to 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 108 through JetSym or the PLC.
The digital servo amplifier JetMove 108 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 trip (x = 100 %) is a result of the following formula:
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)
x t
( )
100%
average motor current
nominal current
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 
 
2
×
1 e
t
T
--- –
–
 
 
 
×
=
t T 1
nominal current
average motor current
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 
 
2
–
ln
×
– =