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A.7.2 Line filter selection - Leakage capacitance
The effect of the line filter is in general limited by the sum of all the leakage capacitances in the compo-
nents connected to the JM-3000. This parasitic capacitance is primarily determined by the motor cables
connected. The capacitances in motors connected form a further factor that cannot be ignored.
Therefore, typical application scenarios were assumed for the development of the filters and the capaci-
tances of Jetter motor cables and motors used as the basis to produce typical total capacitances for
which the filters were designed. To Jetter components the following applies:
Jetter cables have a value of 0.47 nF/m
y
Jetter motors have a value less than or equal to 10 nF
y
For the 600 m filter variant, an application with 12 motors each with a cable length of 50 m is assumed for
the design. With the above data, there is a total capacitance of 12 x 10 nF + 12 x 50 m x 470 pF/m = 402
nF. The permissible total leakage capacitances for the other line filters can be determined accordingly.
Overview of the permissible leakage capacitances for the line filters
Filter type
JEMCxx.120
JEMCxx.240
JEMCxx.600
Table A.9 Total leakage capacitance on line filters
Detailed consideration is necessary in applications with a larger number of axes or with long motor
cables. Detailed consideration is also necessary if cables from other suppliers are used and these cables
are not designed to have low capacitance, and if motors from other suppliers or special motors are used.
As the basis for the estimation of the permissible total cable length, use:
Lg = (Cx – Cm) / Ck
Key:
Lg = Sum of the cable length for all axes connected [m]
Cx= Permissible total leakage capacitance of the line filter (see table) [nF]
Cm= Sum of the parasitic capacitances in all motors connected [nF]
Ck = Capacitance of the motor cable used in [nF/m]
Example:
The JM-3000 system features the possibility of operating up to 24 axes on one supply unit. Selected
mains filter is in JEMCxx.600.
Due to the capacitance contributed by the motors of 240 nF (24 x 10nF), a total cable length of Lg = (402
nF-240 nF)/0.47 nF/m = 344 m is permissible.
That is an average per axis of 14.3 m on a "600 m filter".
74
Permissible total leakage
capacitance Cx [nF]
176
261
402
JetMove 3000 Supply Unit
Max. cable length that can be
connected for 12 axes [m]}
120
300
600
Jetter AG
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