Micromod MOD: 30ML and Modcell Maintenance for 2001N, 2002N, and 1800R - Manual (Page 132)

Technical Notice
On examining the problem in detail it was determined that this is an invalid diagnostic and does not affect
the output signal to the field. After reviewing the design schematics with one of the development
engineers, it was determined that there may have been a change in a vendors' component tolerance
used inside the modules, causing the readback diagnostic error. It is believed to be a timing issue.
It is not uncommon for a vendor to change a component's speed, timing or tolerance without notifying
their customers. This has been encountered before on other products.
Because this does not cause any change in the field output and clears on the next scan cycle, the
recommended course of action is to disable the diagnostic. This diagnostic has been observed and
monitored on processes including industrial boiler controls and there has been no effect on the process.
To disable this particular diagnostic, set AOMn.AOMERRS to 1 (n = analog output module occurrence
number). In ViZapp, this error can be suppressed by checking the Module error box on the Diagnostics
tab of the AOM block. If, for a particular application, you wish to ensure there is not really a readback
problem on the output, the readback signal can be compared to the calculated output, with a small time
delay. The result of this comparison can be forwarded to a PA or PAD block.
Topic: MOD 30ML/Modcell Technote: TNML1001-2
MicroMod Automation, Inc. Rev. 08-July-2003
AOM Readback.doc Page 2 of 2