Basic PLC functions, advantages/disadvantages?

I did a large refinery tank farm control system back around 1985, Totally redundant Mod-icon (3) 528 PLC's and Mod-view operators touch screen console. The farm consisted of 32 tanks and 128 MOV's all at the end of a cross country pipeline and feeding a large refinery. It was a fun project, and i programmed the mod-view in pascal. I guess that would fall into the rack mount category.

Whats up i'll aid u A Programmable good judgment Controller, PLC, or Programmable Controller or common sense field is an digital device used for automation of industrial tactics, such as control of equipment on factory meeting traces. Unlike common-cause computer systems, the p.C.Is designed for a couple of inputs and output arrangements, elevated temperature ranges, immunity to electrical noise, and resistance to vibration and have an effect on. Programs to control computing device operation are commonly saved in battery-backed or non-risky memory. A p.C.Is an instance of an actual time process due to the fact that output results need to be produced in accordance with enter stipulations inside a bounded time, or else unintended operation will influence. An illustration for u.,........... Example As an illustration, say the ability needs to store water in a tank. The water is drawn from the tank with the aid of an extra system, as needed and our instance system ought to control the water degree within the tank. Utilising only digital alerts, the %has two digital inputs from float switches (tank empty and tank full). The percentuses a digital output to open and shut the inlet valve into the tank. If each float switches are off (down) or best the 'tank empty' change is on, the %will open the valve to let more water in. If handiest the 'tank full' change is on, the valve turns off. Each switches being on would sign that something is improper with some of the switches, because the tank can not be both full and empty while. Two glide switches are used to hinder a 'flutter' situation where any water utilization activates the pump for an extraordinarily brief time inflicting the system to wear down turbo. An analog procedure would use a load mobile (scale) that weighs the tank, and an adjustable (throttling) valve. The p.C.Would use a PID suggestions loop to manipulate the valve opening. The weight mobile is connected to an analog enter and the valve is connected to an analog output. This approach fills the tank rapid when there may be much less water in the tank. If the water stage drops swiftly, the valve can also be opened broad. If water is simplest dripping out of the tank, the valve adjusts to slowly drip water back into the tank. In this procedure, to avoid 'flutter' changes that may put on out the valve, many p.C. Comprise "hysteresis" which well-nigh creates a "deadband" of exercise. A technician adjusts this deadband so the valve strikes only for a big trade in price. This may in turn shrink the motion of the valve, and shrink its put on. An actual system might combine both approaches, utilizing flow switches and easy valves to hinder spills, and a expense sensor and rate valve to optimize replenish rates. Backup and preservation methods could make a real process very problematic. Hope this is the quality answer........ All the fine