ACL CSC400 Installation And Operation Manual page 61

Modbus Communications Troubleshooting
# Issue
1 Modbus Master can't read
temperature values from
CSC400 (or any other
data)
2 Modbus communication
interrupted, noise issues
suspected
3 Modbus PC Master
communication with
CSC400 interrupted
Possible Reason
RS485 cable isn't connected
properly
Modbus Slave ID (address) is
different than the address used for
the CSC400
Power to the CSC400 may have
been interrupted
Inappropriate, non-twisted pair
cable has been used for the
RS485, for long distances
Inadequate or ineffective
grounding
Power to the CSC400 may have
been interrupted
If a USB-to-RS485 conversion
cable has been used, the PC test
software may have lost
connection to the virtual COM
port, or noise may have interfered
with USB communications.
need to be boosted to 12.5VDC if multiple large
solenoids are attached to one solenoid output.
Corrective Action
Ensure the wires for the RS485 cable are connected
properly at the CSC400 and at the master and that the
screw terminals are gripping the metal wire, not the
insulation.
Wires may also become damaged with frequent
bending or if they've been pinched. Ensure that the
RS485 signal wires haven't been broken by testing
continuity.
Verify that the address used by the master to
communicate with the CSC400 matches the address
set in the CSC400.
Try using the default address: "2".
The master may need to poll a variety of modbus
addresses (from 1 to 247) to find slaves that respond.
Verify the CSC400 has power locally.
Ensure that an appropriate twisted-pair cable (like
CAT5e cable, or other appropriate cable) is used for
the RS485 bus.
Ensure that an adequate connection has been made
between the earth ground terminal on the CSC400 and
an appropriate earth ground external to the CSC400
(eg: thick spike in the ground, underground water
pipes, earth ground pin on an AC wall outlet).
Ensure that unused, non-power sourcing wires in any
RS485cable are grounded.
Connect the "Isolated GND" terminal on the CSC400
Controller to the CSC400 earth ground terminal to
provide a localized ground path for noise. (Attach
GND jumper on Rev 2B cards and later)
Verify the CSC400 has power locally.
Unplug the USB-to-RS485 conversion cable from the
USB port on the PC, wait 10 seconds, then plug it
back in. Retry connecting to the COM port in the test
software.
Add an industrial-rated USB hub between the PC and
the USB-to-RS485 cable. Ensure that the hub is
powered locally, not bus-powered from the PC.
Refer to Troubleshooting item # 2 for additional
61