The DOUT channel can have one of the following status values:
· Open load
· No contact (expansion modules)
The possible status and and the triggering conditions vary between module and pin types. There are more diagnostic methods than there are statuses on the list above, and there are even more possible wiring errors or other problems with the load that can trigger these diagnostic methods.
In the IQANdesign user manual, the section "Value and status" lists all statuses along with information on whether the status generates a dialog message and/or system log event. The status is also seen when measuring in IQANdesign/IQANrun.
The status when the function group or the expansion module the DOUT is located on is disabled. It is a good design practice to disable optional functions to avoid triggering e.g. open load errors when an option is not fitted.
The normal status.
This is the status used when an open circuit in the wiring is detected. Loads with high resistance and other errors may also trigger this status.
The MC3 and MC4x have Digital outputs that combine several diagnostic tests, e.g. monitoring of both the voltages on the high- and low-side switches as well as current measurement.
The MC3 and MC4x Appendix A information specifies:
-A load resistance as the open load threshold when the DOUT is OFF
-The under current threshold that will trigger open load when the DOUT is on.
When these output are ON, a current below the under current threshold results in an open load. To use the outputs with loads that draw a lower current (e.g. LED:s and small relays), it is possible to disable this test with the IQANdesign pin property DOUT under current detection.
MC4x Appendix B information also specifies:
-External wiring faults, the state when these are detected and expected DOUT status.
The XC21, MD4 and MC43 have low-side digital outputs that detect open load when the DOUT:s are OFF.
The overload status is used when the diagnostics detect a too high current, or a fault that would cause a too high current. The most intuitive cases are short to ground on high-side or low-side.
As with open load detection, the MC3 and MC4x modules have methods for detecting overload both when the DOUT is on and when it is off.
DOUT:s do not have the start-block status, but related to start-block is the restart behavior after any error status.
The DOUT will remain in its last error status (e.g. open load) until it is activated/deactivated to test again. It is possible to further restrict DOUT restart with MC3/MC31 module properties in IQANdesign.
Error, Critical Error
On MC3 and MC4x, diagnostics tests that are primarily designed to detect module internal faults will trigger the status Error or Critical error.
Unusual installation problems may also trigger this status. On MC4x and MC4xFS, it is possible to get the DOUT status Error after a dip in supply voltage, this could occur in weak 12V systems.
All I/O on expansion modules are set to the status No contact if the master detects a module timeout. Expansion module traffic resumes automatically, but all activated outputs will remain in No contact as a form or start block function, until they are given a zero command.
Customer support service by UserEcho