70
Unidrive M Modular Installation Guide
Issue Number: 2
Cable layout
Figure 6-15 indicates the clearances which should be observed around
the drive and related ‘noisy’ power cables by all sensitive control signals
/ equipment.
Figure 6-15 Drive cable clearances
N
Any signal cables which are carried inside the motor cable (i.e. motor
thermistor, motor brake) will pick up large pulse currents via the cable
capacitance. The shield of these signal cables must be connected to
ground close to the motor cable, to avoid this noise current spreading
through the control system.
Feedback device cable shielding
Shielding considerations are important for PWM drive installations due to
the high voltages and currents present in the output (motor) circuit with a
very wide frequency spectrum, typically from 0 to 20 MHz.
The following guidance is divided into two parts:
1.
Ensuring correct transfer of data without disturbance from electrical
noise originating either within the drive or from outside.
2. Additional measures to prevent unwanted emission of radio
frequency noise. These are optional and only required where the
installation is subject to specific requirements for radio frequency
emission control.
To ensure correct transfer of data, observe the following:
Resolver connections:
•
Use a cable with an overall shield and twisted pairs for the resolver
signals
•
Connect the cable shield to the drive 0 V connection by the shortest
possible link ("pigtail")
•
It is generally preferable not to connect the cable shield to the
resolver. However in cases where there is an exceptional level of
common-mode noise voltage present on the resolver body, it may be
helpful to connect the shield there. If this is done then it becomes
essential to ensure the absolute minimum length of "pigtails" at both
shield connections, and possibly to clamp the cable shield directly to
the resolver body and to the drive grounding bracket.
•
The cable should preferably not be interrupted. If interruptions are
unavoidable, ensure the absolute minimum length of "pigtail" in the
shield connections at each interruption.
Encoder connections:
•
Use a cable with the correct impedance
•
Use a cable with individually shielded twisted pairs
•
Connect the cable shields to 0 V at both the drive and the encoder,
using the shortest possible links ("pigtails")
•
The cable should preferably not be interrupted. If interruptions are
unavoidable, ensure the absolute minimum length of "pigtail" in the
shield connections at each interruption. Preferably, use a connection
method which provides substantial metallic clamps for the cable
shield terminations.
The above applies where the encoder body is isolated from the motor
and where the encoder circuit is isolated from the encoder body. Where
there is no isolation between the encoder circuits and the motor body,
and in case of doubt, the following additional requirement must be
observed. This gives the best possible noise immunity.
•
The shields must be directly clamped to the encoder body (no
pigtail) and to the drive grounding bracket. This may be achieved by
clamping of the individual shields or by providing an additional
overall shield which is clamped.
N
The recommendations of the encoder manufacturer must also be
adhered to for the encoder connections.
N
In order to guarantee maximum noise immunity for any application
double shielded cable as shown should be used.
In some cases single shielding of each pair of differential signals cables,
or a single overall shield with individual shield on the thermistor
connections is sufficient. In these cases all the shields should be
connected to ground and 0 V at both ends.
If the 0 V is required to be left floating a cable with individual shields and
an overall shield must be used.
Figure 6-16 and Figure 6-17 illustrate the preferred construction of cable
and the method of clamping. The outer sheath of the cable should be
stripped back enough to allow the clamp to be installed. The shield must
not be broken or opened at this point. The clamps should be installed
close to the drive or feedback device, with the ground connections made
to a ground plate or similar metallic ground surface.
Optional braking
resistor and overload
Do not place sensitive
(unscreened) signal circuits
in a zone extending
300mm (12”) all around the
Drive, motor cable, input
cable from RFI filter and
unscreened braking resistor
cable (if used)
300mm
(12in)
Master
9E 10E 9A
NOTE
NOTE
NOTE
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