The limit values are values that can be set within the measuring range of a measured
variable. For each measuring channel a Limit
[1]
can be set for exceeding, i.e. the meas‐
ured value is greater than the limit value and a Limit
[2]
can be set for undershooting, i.e.
the measured value is less than the limit value. As the controller only has two limit value
relays, there is an option of selecting a limit value
‘range’
. An upper and lower limit are
set as a limit value
‘range’
. If the measured value is above or below the
‘range’
, then a
limit value transgression exists.
If the limit is exceeded for longer than
[the Control time lim. val. (∆t on)]
, then an error
message will be triggered that has to be acknowledged and the alarm relay is deacti‐
vated. If the
[controller]
is also set to
[OFF]
then the control process is stopped.
[Lower lim]
means that the limit criterion has been transgressed by undershooting of the
lower limit
[High limit]
means that the limit criterion has been transgressed by exceeding of the
upper limit.
The controller has the option of defining
[Hysteresis limit values]
.
[Hysteresis]
works towards rectifying the limit transgression, i.e. if the
[limit 1 upper]
of,
for example, pH 7.5 has been exceeded by a set hysteresis limit of, for example, pH
0.20, then the criterion for limit transgression is redundant when the value drops below
the lower limit of pH 7.3. The hysteresis behaviour for undershooting a
[Low limit]
func‐
tions in a similar way (here the hysteresis value is added to the limit). In this way it is pos‐
sible to forego an external relay in self-retaining mode.
If the limit is exceeded for longer than the
[Delay period limits∆t on]
, then an acknowl‐
edgeable fault message will be triggered and the alarm relay is deactivated. If the
[controller]
is also set to
[OFF]
then the control process is stopped.
Setting the
[Limit values]
121
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