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External Mismatch Alarm in Triconex AO Card
"External Mismatch" Alarm in Triconex AO Card

All AO card in the Triconex are showing External Mismatch Alarm in the Enhanced Diagnostic Monitor. How to troubleshoot this as the system is online. What could be the possible reasons for this alarm?

What is the model# and type of AO card?


>All AO card in the Triconex are showing External Mismatch
>Alarm in the Enhanced Diagnostic Monitor. How to
>troubleshoot this as the system is online. What could be the
>possible reasons for this alarm?

Customer Advisories are intended to inform you of the possibility of a situation occurring at system installations, and the identified resolution. Schneider Electric recommends that our customers consider taking action to help prevent occurrence of the identified situation during your production process.

Model 3701/C/C1, 3700A/C/C1, 3805E/C/C1, 3805H/C/C1, 3806E/C/C1, and 3807/C/C1 Tricon Analog modules manufactured from January 2013 to October 2015 have a higher than normal Field Failure Rate.

This is due to a combination of more aggressive flux and weakness in the resistor design.


The affected modules may report the following diagnostic messages: "External error mismatch", "internal loop back error leg A, B, or C", "No communication on A leg", "Internal Loop Fault Error", "Sanity test failed error" or "Bad Integer Inputs 1-32."

Schneider Electric has confirmed that the issue caused by the use of the resistor component is leg-centric, fully diagnosable, and the module's safety-related operation is not affected if the component stops working.

This condition causes a fault to be detected on a leg, which generates an alarm in the system. This condition will not disrupt your process as long as you replace the module within the estimated Mean Time to Repair period.

Please follow this guidance, published in the Tricon Safety Considerations Guide for Tricon v9-v11 Controllers:

All Tricon logic solver faults can be repaired online without further degradation of the system and should be performed before a second fault occurrence to maintain the highest availability of the system. The highly effective means of modular insertion and replacement of faulted Tricon system components is transparent to the operation of the system and the ease of replacement mitigates the risk of systematic and human induced failure as defined by IEC 61508. It is highly recommended that a faulted component be replaced within industry accepted Mean-Time-To-Repair (MTTR) periods.


Affected modules will have their warranty period extended to seven years from the date of manufacture.

All modules returned to Lake Forest for repair will have new resistors installed. The new resistors have a protective fill that helps prevent flux from contaminating the resistive element.

Please identify M02363 in the RMA request.


If you have any questions regarding this article, please contact your local Service Representative or a Schneider Electric Support Center at:

GCS Center
America's GCS
Asia Pacific GCS
Foxboro MA USA
Baarn NL
+86 21 37180086

+86 21 37180196
America's GCS
Asia Pacific GCS