Basic Information On Relay Functions; Monitoring; Limit Indicator - Xylem DIQ/S 281 Operating Manual

DIQ/S 281
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6.2

Basic information on relay functions

This chapter describes general basic information concerning the following relay
functions:
 Monitoring (see section 6.2.1)
 Limit indicator (see section 6.2.2)
 Proportional output (see section 6.2.3)

6.2.1 Monitoring

When using a relay for monitoring, a relay action (
certain states occur. This function is suitable, for example, for the monitoring of
errors in the system.
For monitoring functions, use the relay preferably as normally
closed (see section 6.6.1). In the case of an error, the relay opens.
As a result, the monitoring function operates even if, for instance,
the supply voltage fails.

6.2.2 Limit indicator

With a limit indicator, a relay switches when a specified limiting value is
exceeded or undercut.
Limit indicators can be used in the following way:
 Monitoring a limiting value using a relay:
when a limiting value (upper or lower limiting value) is exceeded or undercut,
a relay switches. The
(see page 98).
 Monitoring two limiting values using two relays:
If the upper limiting value is exceeded or undercut, a relay switches, and if
the lower limiting value is exceeded or undercut, another relay switches. The
Open Close
or
If the simple monitoring function (
relays is not sufficient, use proportional output (see section 6.2.3).
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Open Close
or
relay actions are possible in each case (see page 98).
Open Close
,
relay actions are possible in each case
Open Close
, ) with one or two
Outputs
) occurs when
97