Safety Considerations Guide for Triconex General ... - ICEWeb

Module Diagnostics 37
Analog Output (AO) Modules
Analog output modules use a combination of comparison and reference diagnostics. Under
system control, each channel is given control of the output sequentially using the 2oo3 voting
mechanism. Each channel independently measures the actual state of an output value by
comparing it with the commanded value. If the values do not match, a channel switch is forced
by voting another channel. Each channel also compares its measured values against internal
references. Using these diagnostics, each channel can be independently verified for its ability to
control the analog output value, thus assuring nearly 100 percent fault coverage and fail-safe
operation under all single-fault scenarios, and most common multiple-fault scenarios.
Analog Output Module Alarms
Analog output module faults are reported to the control application. These alarms can be used
to increase availability during specific multiple-fault conditions. Loss of field power or logic
power is reported to the control application.
Digital Input (DI) Modules
Digital input module pointsuse force-to-value diagnostics (FVD). Under system control, each
pointis sequentially forced to a test value. The forced value is maintained until the value is
detected by the system or a time-out occurs. Using the integral FVD capability, each point can
be independently verified for its ability to accurately detect a transition to the opposite state,
typically every 500 milliseconds. (For more information on fault reporting time, see Calculation
for Diagnostic Fault Reporting Time on page 39.) These diagnostics are executed independently
by each channel, thus assuring nearly 100 percent fault coverage and fail-safe operation under
all single-fault scenarios, and most common multiple-fault scenarios.
Digital Input Module Alarms
Digital input module faults are reported to the control application. These alarms can be used to
increase availability during specific multiple-fault conditions. Loss offield power or logic power
is reported to the control application.
Digital Output (DO) Modules
Digital output modules use output voter diagnostics (OVD). Under system control, each output
point is commanded sequentially to both the energized and de-energized states. The forced
state is maintained until the value is detected by the system or a time-out occurs (500
microseconds, typical case; 2 milliseconds, worst case). Using the integral OVD capability, each
point can be independently verified for its ability to a transition to either state, typically every
500 milliseconds. (For more information on fault reporting time, see Calculation for Diagnostic
Fault Reporting Time on page 39.)
Safety Considerations Guide for Triconex General Purpose v2 Systems