Dynisco ATC990 Manuale di applicazione e configurazione - Pagina 11

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Automatic
stand‐by

ATC990

Automatic
stand‐by
Feature



The
automatic
stand‐by
function
avoids
overshoots
following
temporary
process
interruptions
(i.e.
if
the
pressure
goes
to

zero)
that
may
cause
the
controllers
integral
component
to
saturate.
When
the
process
restarts,
a
saturated
output
is
likely
to

cause
an
excessive
and
potentially
dangerous
overshoot
(starting
the
motor
at
full
speed).
This
feature
is
not
active
while
in

manual
control
mode.



The
parameters
are:

1. Pressure
Stand‐by
Threshold

Automatic
stand‐by
pressure
threshold
value
to
switch
controller
into
the
automatic
stand‐by
sequence
(in
physical

units
from
0
to
15
%
of
full
scale
or
OFF).
Input
excursions
of
[SP±
Threshold]
start
the
automatic
stand‐by
feature.

If
set
to
OFF,
the
automatic
stand‐by
feature
is
disabled.

2. Pressure
Stand‐by
Recovery
Time

The
maximum
of
time
(from
1
to
60
seconds)
the
automatic
stand‐by
sequence
is
allowed
to
continue.
If
the
excursion

lasts
longer
than
this
time,
manual
mode
with
0%
controller
output
is
applied
(emergency
stop).

3. Pressure
Stand‐by
Active
Limit

An
active
power
limitation
value.
It
limits
power
to
the
"known
good
steady
state
power"
required
±
the
Pressure
Stand‐
by
Active
Limit
value.
This
improves
safety
for
a
very
sensitive
reacting
pressure
processes
by
avoiding
large
deflections.



Using
Automatic
stand‐by




The
automatic
stand‐by
function
is
activated
by
setting
the
Pressure
Stand‐by
Threshold
to
a
value
other
than
OFF.
The

unfiltered
controller
input
is
monitored
(not
the
slower
filtered
display
value),
and
when
it
leaves
the
band
above
or
below

the
setpoint
set
by
the
"Pressure
Stand‐by
Threshold"
parameter,
the
output
is
immediately
set
to
the
steady
state
value

stored
when
the
process
was
first
stable


If
the
input
recovers
within
the
"Pressure
stand‐by
recovery
time",
the
controller
waits
for
two
and
half
time
the
integral

value
(2.5
*
Ti)
and
then
returns
to
normal
"running"
conditions.



If
the
process
input
does
not
recover,
the
output
remains
at
the
steady
state
value
until
the
Pressure
stand‐by
recovery
time

has
elapsed,
at
which
time
the
controller
is
switched
to
manual
mode
at
0%
power.



Note:
if
the
Pressure
stand‐by
recovery
time
is
set
to
OFF,
the
controller
enters
manual
mode
at
the
stored
steady
state

value,
immediately
the
Pressure
Stand‐by
Threshold
is
exceeded.

Changing
the
setpoint
while
the
Automatic
stand‐by
is
active
will
cancel
the
stand‐by
sequence.
It
will
not
be
able
to
activate

until
a
new
steady
state
value
has
been
found.



**The
old
model
ATC880
monitor
the
input
and
output
the
feature
only
began
if
the
threshold
was
passed
and
the
output

was
at
saturation.
ATC990
monitors
the
input
level,
but
not
output
saturation
because
the
process
could
see
heavy

disturbances
before
the
output
is
saturated.



(1.
see
Finding
the
Steady
State
Power
below)
.