Emc Considerations - JVL MIS17 Series User Manual

2.7
2.7.1

EMC considerations

The MIS family of motors eliminates the traditional problems with noise from long motor
cables that emit noise and feedback cables that are sensitive to noise from external
sources.
However, it is still necessary to be aware of noise problems with communications cables
and the 8 general-purpose inputs and outputs.
Whenever a digital signal changes level quickly, a noise spike is generated, and is trans-
ferred to the other wires in the same cable, and to a lesser degree to wires in other ca-
bles located close to the cable with the switching signal. A typical example is when a
digital output from the MIS motor changes from low to high to drive a relay. If this digital
output signal is transmitted in a multi-wire cable together with the RS-485 signals, there
is a high risk that the RS-485 signal will be affected to the extent that the communication
will fail, and require software retries.
If communication is used during operation, and operation includes either digital input sig-
nals or digital output signals, some precautions must be taken to avoid noise problems.
The following sections describe a number of measures which can be taken to solve noise
problems. In most installations, no special measures will be required, but if noise prob-
lems are experienced – and/or must be avoided – it is highly recommended the instruc-
tions below are followed.
2.7.2 Use short cables
The shorter a cable is, the less noise problems it will induce. Be sure to keep the cables
as short as possible. Instead of curling up the cables, cut them off at the minimum re-
quired length.
2.7.3 Use separate cables
Avoid running digital signals in the same multi-wire cables as RS-485 communication sig-
nals.
On some models of the MIS motors, the same connector contains both RS-485 signals
and I/O signals – typically the I/Os 1-4.
In many applications, far from all inputs and outputs are used. If only up to four I/Os are
required, consider using only I/Os 5-8 which are typically available via another connector
on the motor.
2.7.4 Use filters
If more than 4 I/Os are needed, consider using I/Os 1-4 for inputs and I/Os 5-8 for out-
puts. It is normally possible to install a hardware filter on the digital input signals before
they enter the cable. With such a (good) filter, noise on the RS-485 signals will not be a
problem.
It is also possible to use filters on the outputs, but it is more difficult. It can be done by
using short cables from the motor to the filters, and then using longer cables from the
filters to the output targets. It may be easier to use a short cable from the motor to a
splitter box, and then split the I/Os in one cable and the RS-485 signals in another cable.
2.7.5 Use termination (resistors) on the RS-485 signals
RS-485 is typically used to connect a single master PC or PLC to one or more motors in
a chain. Both ends of the chain must have a 120 Ohms termination resistor connected
between the A- and B+ signals. There is typically a terminating resistor in the master PC
or PLC, but there is no termination inside the motors. Therefore an external resistor
must be connected at the end of the cable out of the last motor in the chain. If the last
motor has no connection cable, a connector with a resistor soldered between the A- and
B+ pins should be used.
JVL Industri Elektronik A/S - User Manual - Integrated Stepper Motors MIS17x, 23x, 34x, 43x
EMC considerations
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