5

Analog Input Discrepancy Reporting

If there is a discrepancy in the data from a set of inputs, so that a channel deviates by more than a configurable percentage from the voted value, the PLC automatically places a message in the I/O Fault Table where it is available to the Logicmaster 90 software and the application program logic.

Discrepancy is calculated for engineering units values inputs. Two distinct discrepancy bands are provided: threshold and limit.

HThe threshold discrepancy occurs where an A, B, or C engineering units input value exceeds a specified percentage of the voted value. For example, if channels A, B, and C report 91, 100, and 111, respectively, the GMR software selects 100 as the intermediate value. If the threshold discrepancy for the input is set to 10%, this yields 90 and 110 as the upper and lower threshold discrepancy values. In this example, channel A is within the threshold band, but channel C is outside, and is discrepant.

HThe limit discrepancy occurs where an engineering units input exceeds a given percentage of the full-scale deflection of the input. For example, if channels A, B, and C report 9, 10, and 15, respectively, then the GMR software selects 10 as the intermediate value. If the limit discrepancy is set to 10% of a 200 full-scale deflection (20 in this case) then no limit discrepancy is reported.

An analog discrepancy is reported where the limit discrepancy and the threshold are both exceeded. Up to two of the three analog inputs may be discrepant at any given time.

Discrepancy faults are latched, but can be cleared by performing an I/O Fault Reset (see chapter 7, Programming).

When a discrepancy occurs, the PLC sets the fault contact for that voted input and adapts according to its configuration. See page 5-25 for information about these fault contacts.

Discrepancy signals are filtered for the configured input discepancy filter time to eliminate transient discrepancies caused by timing differences.

GFK-0787B

Chapter 5 Diagnostics

5-13

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Image 73
GE GFK-0787B user manual Analog Input Discrepancy Reporting