Quantum MP User Guide
45
Issue: A4 www.emersonct.com
4.12.5 Surge immunity of control circuits - long
cables and connections outside a building
The input/output ports for the control circuits are designed for general
use within machines and small systems without any special precautions.
In applications where they may be exposed to high-energy voltage
surges, some special measures may be required to prevent malfunction
or damage. Surges may be caused by lightning or severe power faults in
association with grounding arrangements which permit high transient
voltages between nominally grounded points. This is a particular risk
where the circuits extend outside the protection of a building.
As a general rule, if the circuits are to pass outside the building where
the drive is located, or if cable runs within a building exceed 30m, some
additional precautions are advisable. One of the following techniques
should be used:
1.
Galvanic isolation, i.e. do not connect the control 0V terminal to
ground. Avoid loops in the control wiring, i.e. ensure every control
wire is accompanied by its return (0V) wire.
2.
Shielded cable with additional power ground bonding. The cable
shield may be connected to ground at both ends, but in addition the
ground conductors at both ends of the cable must be bonded
together by a power ground cable (equipotential bonding cable) with
cross-sectional area of at least 10mm
2
, or 10 times the area of the
signal cable shield, or to suit the electrical safety requirements of the
plant. This ensures that fault or surge current passes mainly through
the ground cable and not in the signal cable shield. If the building or
plant has a well-designed common bonded network this precaution
is not necessary.
3.
Additional over-voltage suppression - for the analog and digital
inputs and outputs, a zener diode network or a commercially
available surge suppressor may be connected in parallel with the
input circuit as shown in Figure 4-13 and Figure 4-14.
Figure 4-13 Surge suppression for digital and unipolar inputs and
outputs
Figure 4-14 Surge suppression for analog and bipolar inputs and
outputs
Surge suppression devices are available as rail-mounting modules, e.g.
from Phoenix Contact:
Unipolar TT-UKK5-D/24 DC
Bipolar TT-UKK5-D/24 AC
These devices are not suitable for encoder signals or fast digital data
networks because the capacitance of the diodes adversely affects the
signal. Most encoders have galvanic isolation of the signal circuit from
the motor frame, in which case no precautions are required. For data
networks, follow the specific recommendations for the particular
network.
4.13 Serial communications connections
The Quantum MP has a serial communications port (serial port) as
standard supporting two wire EIA485 communications. Please see Table
4-22 for the connection details for the RJ45 connector.
Figure 4-15 Serial communications port
Table 4-22 RJ45 connections
The communications port applies a two-unit load to the communications
network. Connectors 2, 3, 7 and shield must always be made to the
serial communications port. Shielded cable must be used at all times.
4.13.1 Isolation of the serial communications port
The serial PC communications port is double insulated and meets the
requirements for SELV in EN50178.
An isolated serial communications lead has been designed to connect
the drive to IT equipment (such as lap-top computers), and is available
from the supplier of the drive. See Table 4-23 for details.
Table 4-23 Isolated serial comms lead details
The “isolated serial communications” lead has reinforced insulation as
defined in IEC60950 for altitudes up to 3,000m.
N
When using the CT EIA232 Comms cable the available baud rate is
limited to 19.2k baud.
4.13.2 Multi-drop network
The drive can be used on a 2 wire EIA485 multi-drop network using the
drive's serial communications port when the following guidelines are
adhered to.
Connections
The network should be a daisy chain arrangement and not a star,
although short stubs to the drive are allowed.
The minimum connections are pins 2 (RX TX), 3 (isolated 0V), 7 (RX\
TX\) and the shield.
Pin 4 (+24V) on each drive can be connected together but there is no
power sharing mechanism between drives and therefore the maximum
power available is the same as a single drive. (If pin 4 is not linked to the
other drives on the network and has an individual load then the
maximum power can be taken from pin 4 of each drive.)
Termination resistors
Pin
Function
1
120
Termination resistor
2
RX TX
3
0V isolated
4
+24V (100 mA)
5
0V isolated
6
TX enable
7
RX\ TX\
8
RX\ TX\ (if termination resistors are
required, link to pin 1)
Shell
0V isolated
In order to meet the requirements for SELV in IEC60950 (IT
equipment) it is necessary for the control computer to be
grounded. Alternatively, when a lap-top or similar device is
used which has no provision for grounding, an isolation
device must be incorporated in the communications lead.
Part number
Description
4500-0087
CT EIA232 Comms cable
4500-0096
CT USB Comms cable
1
8
WARNING
NOTE