Emerson Vission 20/20, Operation And Service Manual

Page: 116 / 258

18 – 4
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 1.9
Section 18 • Auxiliary Input / Output
• High Trip:
• De fi nes the upper limit of the input value that
when exceeded will generate a trip.
Analog Outputs
This screen allows to map any standard analog input or
auxiliary input to any of the four analog auxiliary out-
puts. There are two pages of auxiliary output con
fi gura-
tion; each consists of two analog auxiliary outputs. For
Auxiliary Outputs Screens, see Figures 18-6 and 18-7.
• Active Input:
• Active Input can be selected from avail-
able standard analog inputs or auxiliary inputs.
Selected Active Input gets mapped to auxiliary
output.
• Run Always:
• “Run Always” option can be selected to en-
able mapped auxiliary output irrespective of the
compressor’s run state. If “Run Always” is not
selected then the mapped auxiliary output is
enabled only when compressor is running.
• Trigger:
• Trigger con fi guration is used to enable / dis-
able auxiliary output according to the con fi g-
ured trigger input. Trigger input can be selected
from available standard analog inputs , auxiliary
analog inputs or digital inputs. Trigger value
and differential in combination with trigger
type (“enable if above / On” or “enable if below /
Off”) enables or disables auxiliary output.
Control
Auxiliary outputs can be PID Controlled or Scalable
Controlled.
PID Control:
P = Proportional (gain):
• Used to adjust the auxiliary output in direct propor-
tion to the difference between the control setpoint
and the active input. The proportional term is a unit
less quantity and is used for coarse adjustment. This
setpoint should be set to the lowest value that gives
adequate control system response. Increasing the
proportional setting increases the control system’s
sensitivity to small process
fl uctuations and the
tendency to hunt.
I = Integral (reset):
• Used to integrate the error over time, to account for
a small error that has persisted for a long time. This
quantity is used for
fi ne adjustment. This setpoint is
used to smooth out process variations. This setpoint
should be set high enough to prevent hunting but
not too high or it will cause control system overshoot.
D = Derivative (rate):
• Used to account for how fast the error is changing,
positively or negatively.
Setpoint :
• Setpoint used by PID engine.
Inverse:
• This option is used to inverse Analog Aux Output
to vary output from 20 mA to 4 mA. Typically used
where normally open solenoids are to be operated.
Negative Error:
• Negative Error option is used when PID should be ac-
tive only if negative error is present (Setpoint is great-
er than Process Variable).
Scalable Control:
• Minimum Input / Maximum Input:
• These setpoints de fi nes minimum and maxi-
mum Input range for con fi gured active input .
• Minimum Output / Maximum Output:
• These setpoints de fi nes minimum and maxi-
mum output. The Auxiliary output produces a
linear value based on these settings.