Triconex Trident, Planning And Installation Manual

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Configuring Output Voter Diagnostics 163
Chapter 4 Installation and Maintenance
Configuring Output Voter Diagnostics
Output voter diagnostics (OVD) is a set of tests that detects failures in the output
voting circuitry of DO Modules only. OVD runs without operator intervention or
awareness and enables the Trident controller to continually verify its own integrity.
The diagnostics operate as follows: During execution, the commanded state of each
point in the output circuitry is momentarily reversed on each of the output drivers,
one after another. I
⁄
O loop-back on the module allows each microprocessor to read
the output value of the point to determine whether a latent fault exists within the
output circuit. If a failure occurs, replace the failed module immediately so that the
fault tolerance capability remains in effect.
Triconex guarantees that a glitch to a load lasts less than 2 milliseconds. To ensure
safety, you should analyze the sensitivity of each load device attached to the
controller for proper operation. The less-than-2-millisecond glitch is tolerated well
by electromechanical devices, such as relays, solenoids, and contacts. For
assistance with load devices that might be sensitive to such glitches, consult a
Triconex Field Service Engineer. If glitches are not tolerable in your controlled
process, disable OVD using TriStation.
Disabling OVD on DO Modules
To enable and disable OVD for testing, use the appropriate system attribute in your
TriStation project.
Leave OVD enabled for several minutes. When testing is done,
disable OVD.
If you disable OVD, be sure to schedule regular maintenance periods to ensure the
overall integrity of the controller. During maintenance, shut down the controlled
process and enable OVD. It is not necessary to cycle the outputs to On and Off
states to ensure complete fault coverage.