A Closed Loop Control System is the most important aspect of Maintenance, Regulation and Stability in any Live Process. Nature itself is self regulated in an intricate fashion, a keen observer can notice the subtle controls. In Human Created Industrial systems we have Process control as a complex science. We can start by understanding a Simple One.
When you fill a Bucket with water, You keep an eye on the
Level of water, as you open the Analog Tap, which is an
equivalent of a Motor operated Valve. Your Eye is an advanced
Optical Sensor, which is able to sense the level by the
computation in the brain, which in turn operates the muscles
of your hand, thru the nervous system. The hand along with the
Water Tap is is the Actuator. As the water fills up close to
the top, you start reduction of the water flow and keep
observing, then as it tops up, you tweak the tap to a trickle.
When it reaches the limit you shut off the tap.
Multi Zone Process Scanners and Controllers
While you are half way filling the bucket, what happens if
you take a short nap, or a friend comes by and you are get
absorbed in conversation, the water overflows and goes waste.
Then someone raises an alarm after the Runaway process
happens. This is of minor consequence, but it is not so in the
case of Temperature, Pressure and also many common systems
like the driving of an Automobile. Remember the gears, brakes,
accelerator to control and steer the car to the correct
destination, a Runaway Process causes an accident.
In Industrial Control when a Runaway process can result in
danger or wastage, it is necessary to have a multi tier
protection. It is also better to limit the open loop maximum
to a level which will not cause much damage. So when you need
that extra heat, power or flow, use booster actuators which
will operate for timed bursts in the beginning of the process.
An independent watchdog controller which will shut off power
supply to the entire system when a runaway possibility is
sensed. This can only be manually turned on after repairing
the failed part or controller. A SCADA interfaced to
communication systems can further alert the security, safety
and fire departments.
30th Aug 2020
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