Detailed description of the operation of the EV

Introduction

As soon as one of the inputs monitored is no longer parameterized within the DFB, the latter signals a fault while updating these outputs:

Any faults detected during a single monitoring cycle are picked up as they appear (STATUS word bit is set to 1, corresponding with output update).

At the end of a monitoring cycle (falling Edge ED input), the ERROR andSTATUS outputs are reinitialized to 0.

Trend diagram

The following diagram shows how the EV_DIA function block works .

Operation

The following table describes the different phases illustrated by the diagram below:

Phase	Description
1	When the EVENT input is different from the VALUE public variable (ENABLE = 1), a fault is detected.
2	The ERROR output changes to 0 when the EVENT input takes on the value VALUE of the public variable.
3	A fault is detected when the EVENT input becomes unstable. This type of fault appears after the status of EVENT input changes twice in the same monitoring cycle. The EVENT input unstable fault (bit 8 of word STATUS goes to 1) , becomes a EVENT different from VALUE fault (bit 1 of word STATUS goes to 1) if there are more than 1000 PLC cycles before a new fault is detected. The EVENT input unstable fault disappears if there are more than 1000 PLC cycles, and also if the EVENT input is always equal to the value specified by VALUE.
4	A fault is detected when COND input is anything other than 1.
5	ERROR output changes to 0 when COND input takes on the value of 1.
6	EVENT input is different from the VALUE public variable: there is no fault as ENABLE input = 0.
7	ERROR output changes to 0 when ED input takes on the value of 0.

DFB operation during power outage

During a cold restart, the DFB initializes the parameters and public variables: