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INTERNAL MODEL CONTROL BLOCK (IMC)
An Advanced Control Block in the MANTRA Process Control System
The Internal Model Control Block (IMC) controls a single process variable by
manipulating a single controller output (similar to a PID Control Block). The IMC Controller has an advantage over a PID Controller when the process has a large deadtime.
For example, control of the weight of paper in the papermaking process has
a large deadtime, because the pulp is added in at the wet end of the machine, and the measurement is performed after the dryers.
A PID controller typically must be detuned to compensate for the deadtime. IMC accounts for
deadtime, thereby achieving tighter control of the process.
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How:
The Internal Model Controller (IMC) provides predictive control on an
error signal calculated from the process variable and setpoint values, compared with the output of an internal model of the process.
The controller uses a first order lag with deadtime model of the
controlled process. Bumpless transfer is implemented using controller output (CO) rate limiter to limit both CO increase and decrease.
The controller output is held within specified high and low limits to
prevent CO windup.
Features:
- Self-Tuning
- Bumpless Transfer (rate limiting of the controller output)
- Full Alarming
- Anti-windup implementation
- PV deadband
- Control of both integrating and nonintegrating processes
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Use Examples:
Flow of Highly Viscous Fluid
Process Variable Flow
Controller Output Valve position
Level Control
Process Variable Level
Controller Output Pump Speed
Temperature Control
Process Variable Temperature
Controller Output Coil or Burner
Flow with Long Deadtime
Process Variable Flow
Controller Output Valve
Paper Weight Control
Process Variable Weight
Controller Output Pulp Flow
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Key Parameters:
- Process Control Parameters
- Setpoint (SP)
- Process Variable (PV)
- PV Dead Band
- Controller Output (CO)
- Manual CO Value
- Minimum CO Value
- Maximum CO Value
- Auto-Manual mode switch
- Rate Limit Pos
- Rate Limit Neg
- Model-Based Parameters
- Model Gain
- Model Time Constant
- Model Deadtime
- Filter Time Constant
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Limits and Alarms
- Positive Dev HiHi Alarm
- Positive Dev Hi Alarm
- Negative Dev Hi Alarm
- Negative Dev HiHi Alarm
- Alarm Deadband
Other Parameters
- Controler Output Direction
- Controller Speed
- Noise Level
- PV Tuning Limit
- Tuning Step Size
- Start Tuning
- Tuning Status
- Warm Init
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