Rockwell Automation 198 Series C Modular DeviceNet Starter Auxiliary User Manual - Manual (Page 134)

6-4 Troubleshooting
Publication 198-UM002A-EN-P December 2001
I/O Module Current Errors
The MDSA system is designed to connect a large number of modules and their various loads
to the DeviceNet power system. The maximum continuous loading of the connection is
about 1.75 A. There are a number of fault codes that indicate problems encountered with this
power distribution bus. If for some reason the bus cannot be powered up, an I/O error
code 10, Unable to Power Bus, will occur. The most likely cause of this type of error is
multiple short circuits due to mis-wiring. This unit also has an instantaneous overcurrent
protection which prevents damage to the control circuitry in the DeviceNet module in the
event that there is a dead short on the bus. This would show up as an I/O error code 12,
Overcurrent. If this fault occurs, the offending module must be isolated and replaced before
attempting to restart the system. I/O error code 13, Short Term Over-Temperature,
indicates that an extremely high current is being drawn by the modules attached to the
DeviceNet module. This condition indicates that some load on the system is drawing a high
level of current. This system should be checked for abnormal loads prior to resetting the
fault. Finally, there is an I/O error code 14, Long Term Over-Temperature. This fault
indicates that a minor but persistent overcurrent condition exists. Attribute 32, I/O bus
current, returns the value of the current flowing in the bus. Using this information, the loads
on the system can be adjusted so that the 1.75 A level is avoided. The DeviceNet module
should not be damaged by the overload condition.
Sensor Undervoltage Error
I/O error code 11, and pneumatic valves Undervoltage, indicates that the bus voltage has
dropped below 19V. Some two wire sensors may not be able to operate properly below this
voltage. Typically, 2-wire sensors that require a minimum of 10V to operate will begin to have
data problems around 18V. If 3- or 4-wire sensors are used, then this warning can be ignored.
When this condition exists, the I/O status bits for the sensor module and the DeviceNet
supplied valve module will indicate invalid data. The data from a 2-wire sensor and status of
the pneumatic valve should be ignored, and the system should be moved to a safe operational
state.
Shorted and Open Sensor Detection
The Sensor Modules support both open and short circuit protection indication. In the event
of a load short on the +24V supply, the PTC in the sensor module will transition and indicate
a short on the sensor. This indication should be coordinated with input from this module to
place the system in a safe state. The open cable detection measures the current drawn from
the +24V, and if it falls below about 100
υ A, the module will indicate a missing cable. In some
applications, it is possible to draw no current from the +24V supply. In this case, the open
signal will activate, but can be ignored. This normally will not be the case when sensors are
used with this module.