Evolution of Industrial Process Control Systems
A closed loop controller is the heart of an
Industrial Automation System. Right from an On-Off Hysteresis
Controller to a Auto Tune PID Controller, we find solutions of
different complexities. Each solution might suit a particular system;
depending on the requirements of Ease-of-use, Cost and Process Type.
The Evolution of Temperature Control
- Bimetal Thermostat
- Analog Dial On-Off Controller.
- Analog Dial Proportional Controller.
- Digital Display - Analog Controller - On-Off.
- Digital Display - Analog Controller -
Proportional.
- Digital Display - Analog Controller - PID.
- Microcontroller Based Process Controller.
(On-Off, Prop., Universal TC, RTD, mA Input)
- Process Profile Controller (Microcontroller
Based).
- Microcontroller Based Fuzzy or Auto-Tune PID
Controller.
- Data Logger, Computer, PLC or SCADA based
Solutions.
Even today, the controllers at every stage of
evolution, from the thermostat to Auto-Tune, are used in many
countries, for many different industrial applications. No solution
above is obsolete! The developing Countries still use
electro-mechanical or semi-automatic means for control in some areas.
A PC based multiplexed scanner controller with
data-acquisition cards and I/O Cards can be solution for Laboratory or
Research. This is used when real time control is not required or where
the control failure will not lead to damage or loss.
A PLC or Microcontroller based controller should
be used with a Analog Controller Protection or Over temperature
Trip-Alarm.
Outputs could be Relay or SSR, Voltage and Current
outputs like 0-10V and 4-20mA are needed sometimes to drive DC/AC
Drives or to control Motorized Valves. Relays and SSR can be On-Off or
Time proportional (PWM). The Cycle times can be 10-20 Secs for
Electromagnetic Relay and around 1 Sec for SSR. This is because
Mechanical Relays and contacters have limited number of operations. The
zero crossing SSR has to be cycled slower than mains frequency.
In Curing rubber, which is one of the more
complicated process, we need a profile based controller, which also
triggers other timers or counters which need to be activated at
different segments.
When a very big area is controlled, with materials
or load placed un-symmetrically, Every corner or section has to have
separate sensor and controller. These are then governed by a SCADA,
Supervisory PLC or Master Controller.
Even a Big Die for Plastic Moulding with an
Unsymmetrical Object or long object to be moulded; needs compensation
for sides which will absorb more heat.
Anantha Narayan
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