Reference Manual

Diagnostics and Fault Handling

47.3.1 Fault Filtering

Purpose

The purpose of the subfunction is to determine whether a fault is

present or absent, see ﬁgure below, and the nature of the fault.

Fault filter

parameters

Fault filter

Disturbance/

Measurement

Fault present/

fault absent

P002833A

Figure 141 Fault Filter

Preconditions and initiation

The selftest and supervision function has detected a disturbance.

Description

All disturbances are ﬁltered before a fault is considered to be present or

absent. The ﬁltering function is adapted to each fault situation for

optimum performance. Each fault has its own speciﬁed fault ﬁlter

parameters. For example, the following parameters (or combinations of

parameters) may be used for the ﬁlter function:

• Frequency of disturbances

−

A frequency which is too high is considered to be a fault

• The measurement value of a parameter

− A parameter exceeding a threshold is considered to be a

fault.

• Time

− A condition which is valid for too long is considered to

be a fault

EN/LZT 720 0008 P2A

2001-11-28

379 (485)

Preliminary