Online Online green 1 sec on/1 sec off On Bus converter OK
Offline Online red n/a Off See "Troubleshooting the RS-485 Netwrok"
Bus Low Data shorted low 3 n/a Blue shorted to any white Green shorted to white or black
Bus High Data Shorted High 4 n/a Blue shorted to green, orange or brown Green shorted to red
Bus overload Bus power overload 1 n/a Green, orange or brown shorted to any white Red shorted to white or black
No sensors No sensor on bus 2 n/a Blue open or disconnect switches off Green open or sensor unplugged
Other faults
Sensor reads 85C or 185F Green, orange and brown open Red open
FAQ’s
• What is the most common cause of “Faults”?
o Water ingress into the wiring or FIB’s is the most
common cause of “Faults”.
• Why are all the sensors on a bus converter “Faulted”?
o All of the sensors on a CMC Intrinsically Safe network
are wired in parallel. A short circuit on one sensor can
short the bus and “Fault” all of the sensors.
• All of the sensors on a single bus converter are indicating
intermittent “Faults” every once in a while?
o The bus may have a partial short circuit. Partial short
circuits can occur after severe electrical storms or due
to water ingress in the wiring. Follow the procedure in
the flowchart but instead of observing the LED’s,
observe the voltage on the blue/white and green/white
pairs. Both pairs should have 4-5VDC present, with the
negative lead on the white wire and the positive lead on
the colored wire.
o You can make a test cable from an old sensor. Join the
white and black wires together and measure between
the white/black wires and the green (data) and red
(power) wires. The test cable can be plugged into a
spare jack in the FIB for testing.
o As indicated in the flow chart, start at the first FIB after
the bus converter and work outwards. If the voltages
return to normal when the outbound cable(s) is
disconnected using the disconnect switches, then the
partial short is further down the network. If the voltages
do not return to normal, disconnect the sensors one a
time to locate the partial short.
• A sensor reads +85
o
C or +185
o
F, what is wrong?
o The red wire in the sensor cable is open. Unplug the
sensor and clean both the plug and jack with 99%
Isopropyl Alcohol. Replace the sensor if the
problem is not resolved.
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