Omron EJ1G, User Manual

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70
Setting Control Specifications
Section 5-3
• Integral action: This control action produces an output that is propor-
tional to the time integral of the control error. An off-
set normally occurs in proportional control, so
proportional action is used in combination with inte-
gral action. As time passes, this offset disappears
and the control temperature (process value) matches
the set point.
• Derivative action: This control action produces an output that is propor-
tional to the rate of change of the input. Since propor-
tional control and integral control correct for errors in
the control result, the control system will be slow to
respond to sudden changes in temperature. The
derivative action performs a corrective action by
increasing the MV in proportion to the slope of the
temperature change.
• Effect of Changes to P (Proportional Band)
• Effect of Changes to I (Integral Time)
• Effect of Changes to D (Derivative Time)
Increased P The curve rises gradually and the
settling time is long, but overshooting
is prevented.
Decreased P Overshooting and hunting occur, but
the set point is reached quickly and
the temperature stabilizes.
Increased I It takes a long time for the process
value to reach the set point. It takes
time to achieve a stable state, but
overshooting, undershooting, and
hunting are reduced.
Decreased I Overshooting and undershooting
occur. Hunting occurs. The process
value rises quickly.
Increased D Overshooting, undershooting, and
the settling time are reduced, but fine
hunting occurs on the changes them-
selves.
Decreased D Overshooting and undershooting are
increased and it takes time for the
process value to reach the set point.
Set value
Set value
Set value
Set value
Set value
Set value