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PRESYS
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Instruments
proportional action whenever a ramp occurs in the controlled variable. The derivative
action provides a quick response at the control output resulting from any rapid
variation in the controlled variable. It is used to eliminate oscillations. Note that on the
DCY-2057 Controller the deviate is applied to the controlled variable; this inhibits the
derivative action whenever the setpoint only is altered.
Proportional control only (P)
The proportional control only, usually results in a response with high overshoot
and presenting a regime error (offset) related to the setpoint value.
Proportional plus integrative control (P + I)
The PI control eliminates offsets, but causes a response with very high
overshoot and a very high stabilization time for the oscillations to cease and the
system to reach a stationary regime.
Proportional plus derivative control (P + D)
The PD control, usually, leads the system to the stationary regime with less
oscillations; however, the offset may still remain.
Proportional plus derivative plus integrative control (P + I + D)
The PID control is a solution incorporating the advantages of the PI control
and the PD control. Therefore, the offset is eliminated by the integrative action. The
derivative action eliminates the overshoot and reduces the oscillations caused by the
PI control.
PID control with current or voltage output
To obtain this form of control one just has to select the PID control mode
within the Control level 5 for the desired control block 1 or 2 and to have voltage or
current output modules as built-in output devices (output 1 for control block 1 and
output 2 for the control block 2).
Time proportioning control
This PID control mode is provided with an ON/OFF output device: SPST relay,
solid-state relay and open collector voltage. Therefore, the difference between this
one and the previous form of control is the presence of output devices. Any one of
those devices may be plugged-in as output 1 for control block 1 and the same applies
to control block 2 which may be equipped with any of those devices to serve
DCY - 2057 Pressure Controller
Maintenance
Page 40
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