DERIVATIVE APPROACH
CONTROL
Derivative action (1) sup-
presses overshoot and (2) speeds
response to upsets. However, it may
not always be possible to do both
with one setting. Depending on the
power/load balance, sometimes de-
rivative tuned for quick response will
not suppress overshoot enough.
Derivative approach control
parameter "dAC" solves this prob-
lem. It tunes overshoot independent
of normal operating parameters by
controlling when derivative action
starts on approach to setpoint. Nor-
mally derivative action is only in pro-
portional band. "dAC" is a multiplier
of proportional band.
The smaller the "dAC" setting,
the closer to setpoint derivative ac-
tion begins. Too small and oxygen
overshoots. Too large and approach
is slowed and stepped.
STEPS:
1. With power, proportional, and
integral parameters tuned, and
derivative time tuned for fast
response to upsets, watch
control process in work mode.
Note approach to setpoint.
3. Repeat steps 1-2 until control is
acceptable.
2. Enter program mode and navi-
gate to "dAC" function on level 1.
If overshoot suppression is
needed, increase multiple of
proportional band. Range is
0.5 - 5.0. If approach is stepped
and slow, decrease multiple.
DERIVATIVE SENSITIVITY
This parameter compensates
when power/load balance is such
that derivative suppresses overshoot
but does not sufficiently speed up
response to upsets.
Derivative sensitivity is frac-
tion multiplier of derivative time.
Range is 0.1 - 1.0. By fractioning
derivative time it speeds action up to
10 times faster.
STEPS:
1. With power, proportional, and
integral parameters tuned, and
derivative time tuned for over-
shoot suppression, watch
control process in work mode,
introduce upset by opening
chamber door(s), and note
speed of response to upset.
18
Proox model 360
version 1.0
2. Enter program mode and navigate
to "dEr.S" function on level 4. To
get to level 4 go to "VEr" on level
3 and press both up and down
buttons and hold for 10 sec-
onds. If response to upset is too
slow, decrease setting (limit is
0.1). If response is too fast
resulting in overcompensation,
increase setting (limit is 1.0).
3. Repeat steps 1-2 until control is
acceptable.
AUTOMATIC TUNING
If oxygen setpoint is sufficiently
far away from outside air (20.8),
Proox 360 can calculate it's own
control parameters. It runs a few
tests on host chamber. Takes a few
measurements. Calculates optimum
control parameters, and sets itself.
If setpoint is not far from ambi-
ent, autotuning will not work.
Autotuning sets all control pa-
rameters. It can't distinguish when
some are not needed. Thus some
jobs autotuned are overtuned.
Even jobs that are autotunable,
usually require some manual tuning
afterwards to fine tune.
Autotuning is most useful in
tough jobs that require complex tun-
ing. Gets you close fast (some-
times very close). Thus saves on
time and gas.
Autotuning instructions will be
in the next version of this manual.
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