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7.1.1 Notes on Aggressiveness
7.2 Troubleshooting Autotune
Autotune, whether using SVI3 DTM, pushbuttons, a DD or a handheld, is the best way to
tune the valve. If it does not work:
Step One
Autotune again using recommended tuning parameters for the valve in use. The SVI3
DTM manual offers you instructions in how to enter these parameters in the Autotune
procedure
.
Alternately
,
try starting tuning from the 5
0
% position.
Setting Aggressiveness
While the SVI3 DTM and the DD allow you to set Aggressive
-
ness, the pushbuttons do not. In all three methods, however, the
Aggressiveness value is inherited from any previously per
-
formed tuning (Autotune or manual). Once Aggressiveness, and
other tuning values are determined, they are stored in NVRAM.
The SVI3 provides a user defined Aggressiveness Level for
auto-tuning, the allowable range varies from -9 to +9 where 0
(Zero) is consider normal tuning. The Aggressiveness Level
influences stroking speed and over-shoot. A negative value
SLOWS stroking speed and helps minimize over-shoot. A posi-
tive value INCREASES stroking speed and may add some
over-shoot. The recommended values for Aggressiveness is 0
for control valves without volume boosters.
In applications with volume boosters and/or quick exhaust
valves the Aggressiveness Level is not as influential. For Auto
-
tuning it is usually between
0
and 3
.
Reduce the volume boost-
ers sensitivity by opening the integral bypass needle valve about
1 to 2 turns. Use caution when adjusting the needle valve so as
to not to damage the seat, close gently to seat and then open 1
or 2 turns
Aggressiveness Dynamic
Lower values of aggressiveness lead to lower PID values and
slower response and less overshoot.
Higher values lead to higher PID values and quicker response
and more overshoot.
Once you have a preferred aggressiveness and you tune once,
all future Autotunes automatically use that same value
,
until
user
-
changed.
NOTE : For small actuators it may be necessary to:
• Use 1/8" tubing for Autotune to work properly.
• Install tamper-proof adjustable needle valve in supply line to SVI; adjust
valve closed enough so autotune runs. Then lock valve setting so it can't be
tampered or changed
