Rockwell Automation 900-TC32 Digital Temperature Controllers, Series B - Manual (Page 348)

Publication 900-UM007D-EN-E - January 2011
6-8 Troubleshooting & Error Indication
Symptom: Cannot Communicate or a Communications Error
Occurs
Table 6.B
Meaning Countermeasures
The communications wiring is not correct Correct the Wiring
The communications line has become disconnected Connect the communications line securely and tighten the screws.
The communications cable is broken. Replace the cable.
The communications cable is too long. The total cable length is 500 m maximum for RS-485 and 15 m maximum for
RS-232C communications.
The wrong communications cable has been used. Use a shielded, AWG24 to AWG14 (cross-sectional area of 0.205 to
2.081 mm2) twisted-pair cable for the 900-TC8 or 900-TC16. Use a shielded,
AWG24 to AWG18 (cross-sectional area of 0.205 to 0.823 mm2) twisted-pair
cable for the 900-TC32.
More than the specified number os communications
devices are connected to the same communications path
for RS-485 communications When 1: N RS-485 communications are used, a maximum of 32 nodes
(including the host node) can be connected.
An end node has not been configured at each end of the
communications line for RS-485 communications. Set or connect terminating resistance at each end of the line. If the 900-TC8,
900-TC16, or 900-TC32 is the end node, use 120-
Ω (1/2-W) terminating
resistance.
The combined terminating resistance with the host device must be
at least 54
Ω.
The specified power supply voltage is not
being supplied to the Controller. Supply the specified power supply voltage.
The specified power supply voltage is not
being supplied to an Interface Converter
(such as the 900-CONVxx). Supply the specified power supply voltage.
The same baud rate and communications
method are not being used by all of the Controllers, host
devices, and other devices on the same communications
line. Set the same values for the baud rate, protocol, data length, stop bits, and
parity on all nodes.
The unit number specified in the command
frame is different from the unit number configured by the
Controller. Use the correct unit number.
The same unit number as the Controller is
being used for another node on the same
communications line for RS-485 communications Set each unit number for a unique node number.
There is a mistake in programming the host
device. Use a line monitor to check the commands. Check operation using a sample
program.
The host device is detecting the absence of a response as
an error before it receives the
response from the Controller. Shorten the send data wait time in the Controller or increase the response
wait time in the host device.
The host device is detecting the absence of a response as
an error after broadcasting a
command. The Controller does not return responses for broadcast commands.