Process Controls
PROPORTIONAL PLUS RESET CONTROL SYSTEMS
PROPORTIONAL PLUS RESET CONTROL SYSTEMS
Proportional plus reset control is a combination of the proportional and
integral control modes.
EO 1.4
DESCRIBE the characteristics of the following types of
automatic control systems:
d.
Proportional plus reset control system
Proportional Plus Reset
This type control is actually a
Figure 22 Response of Proportional
Plus Reset Control
combination of two previously
discussed
control
modes,
proportional
and
integral.
Combining the two modes results
in gaining the advantages and
c o m p e n s a t i n g
f o r
t h e
disadvantages
of
the
two
individual modes.
The main advantage of the
proportional control mode is that
an immediate proportional output
is produced as soon as an error
signal exists at the controller as
shown in Figure 22.
The
proportional
controller
is
considered a fast-acting device.
This immediate output change
enables the proportional controller
to reposition the final control
element within a relatively short
period of time in response to the
error.
The main disadvantage of the proportional control mode is that a residual offset error exists
between the measured variable and the setpoint for all but one set of system conditions.
The main advantage of the integral control mode is that the controller output continues to
reposition the final control element until the error is reduced to zero. This results in the
elimination of the residual offset error allowed by the proportional mode.
Rev. 0
Page 33
IC-07
