Detcon 880S-N4X - Manual (Page 33)

880-N4X
880-N4X Instruction Manual Rev. 1.0 Page 29 of 40
6.0 Trouble-shooting
6.1 Sensor Faults
The unit is set up such that Sensor faults will set Fault alarms associated with that sensor. If a sensor goes into
a fault condition, that channel will flag a fault. From the “Main Screen” each channel can be quickly viewed
to see which channel is causing the fault. That sensor should be then checked to find the cause of the fault.
Faults are logged in the Alarm History for aid in tracing intermittent sensor problems. Refer to the appropriate
sensor manual for more information on trouble-shooting sensor faults.
6.2 Troubleshooting RS485 Networks
The first step in finding the bad device or several bad devices is to start at the master:
1. Disconnect the data wires (A & B) from the output terminal blocks.
2. Connect a working slave device directly to the master (attached directly to the output terminal blocks)
and make sure that it is functional. If it is not, replace the master’s transceiver chip or board. In the
case of an 880 Controller, this would be the FA-ISOCON Module.
3. Once this is done stop the master from communicating, but do not power it down. This is
accomplished on the Model 880 by unplugging the phone jack connection to the FA-ISOCON
Module.
4. Unplug all of the slave devices from the data bus.
5. Disconnect the working device connected in Step 2, and re-connect the data bus wires (A&B) to the
master.
6. Use a voltmeter to measure the voltage across the A and B wires and write the reading down. This
reading should be 400-500 millivolts.
7. Go to the first slave device. Re-connect or plug the device in and measure the voltage across A and B.
Write down the reading. The measurement taken should be 400 to 500 millivolts. If the voltage is not
within the specified range, verify that all devices have been unplugged from the data bus.
8. Unplug the first device and proceed to the next slave device. Record the meter readings. Again the
reading should be 400-500mV. If the reading is not 400-500mV a wiring problem may exist, or the
transmitter may be non-operational.
9. Repeat the procedure with each slave device, recording the readings along the way. If any of the other
readings taken are above or below the first reading by more than 50 millivolts, that unit’s transmitter
or the module should be replaced.