Industrial Process Control Circuits
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
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 No solution above is obsolete!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.
The Evolution of Temperature Control
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.
20th Mar 2020
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