Dynisco ATC990 Manuale di applicazione e configurazione - Pagina 12

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Automatic
stand‐by
Example



For
example,
in
a
process
with
these
conditions
set:
Setpoint=6000;
Pressure
Stand‐by
Threshold
=200
Stand‐by
Recovery

Time=30seconds;
Stand‐by
Active
Limit=20.0
and
Integral
Time(Ti)=10seconds

1.
Stand‐by
begins
immediately
at
SP+Threshold
(6200)
or
SP‐Threshold
(5800).

2.
If
normal
input
returns
(within
band
of
5801
to
6199)
in
less
that
the
recovery
time,
normal
power
resumes
after
2.5x

the
integral
time
(25s).

3.
If
normal
input
does
not
resume
in
in
less
that
the
recovery
time,
0%
manual
mode
power
is
applied.
The
user
must

return
the
controller
to
automatic
mode
and
allow
a
new
steady
state
power
to
be
stored
before
the
feature
can

become
active
again.

4.
If
the
recovery
time=OFF,
manual
mode
is
instantly
applied,
with
power
set
to
the
steady
state
value.

Finding
the
Steady
State
Power
For
a
stable
(steady
state)
condition,
the
process
value
must
be
inside
the
requested
band
[Setpoint
±Pressure
Stand‐by

Threshold]
for
more
than
one
minute.
The
power
level
needed
to
achieve
the
stable
condition
is
called
the
steady
state
value.

See
figure
1a
below.

Once
calculated
the
stored
value
remains
unchanged
until
there
is
a
change
of
the
setpoint,
or
the
controller
is
changed
from

automatic
to
manual
mode.
If
this
happens,
a
new
steady
state
value
must
be
found,
and
the
automatic
stand‐by
feature

cannot
function
until
it
has
been
stored.




Finding
Steady
State
Power

Figure
1a



Using
Stand‐by
Active
Limit.



In
addition
to
the
automatic
stand‐by
feature
itself,
further
protection
to
the
process
is
given
by
the
Stand‐by
Active
Limit.
Its

purpose
is
to
limit
the
output
swing
possible
in
very
sensitive
reacting
pressure
process.
This
works
by
limiting
the
power

applied
to
the
process
to
not
more/less
than
the
stored
steady
state
value
±
the
Stand‐by
Active
Limit
set
by
the
user.
See

figure
1b
above.



If
the
stored
steady
state
value=50%
and
stand‐by
active
limit=20%,
the
overall
limits
would
be
30%
to
70%.



.
.



Active
Power
Limiting

Figure
1b