Jetter JM-204-480, User Manual, Page: 40 / 126

5 Technical Data
40 Jetter AG
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 register of JetMove 204-480 through JetSym or the
PLC.
The digital servo amplifier JetMove 204-480 calculates the percentage of motor
power loss according to the following formula:
x(t) = displayed value of motor power loss in %
t = Time since start of motor running it with the average 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 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 the following ones:
With these parameters the 100 % error level will be reached if, for example the motor
is run by a current of 8 A for about 8 minutes and 30 seconds.
5.2.3 Motor overload protection according to
UL
The UL standard prescribes a motor overload detection for a servo amplifier that
meets the following points:
The "trip current" is defined to be 1.15 times the user-set nominal current.
Continuous rated current: 4 A
Overload factor: 2
Motor time constant: 1800 s (30 min.)
x t
( )
100%
average motor current
set current
-----------------------------------------------------
 
 
2
×
1 e
t
T
--- –
–
 
 
 
×
=
t T 1
set current
average motor current
------------------------------------------------------
 
 
2
–
ln
×
– =
Important
Because of the fact that after reset the I²t calculation always starts with zero, the
motor overload calculation is wrong if the motor is already hot when the digital
servo amplifier JetMove 204-480 is switched on (i. e. at the time of parameters of
I²t calculation are written after switching on 24 V logic power supply).