Control Systems

Electronic devices used in different machining industries or in our daily life must be functioning with a control system. Controlling means switching the device ON or OFF, running time, and managing temperature, lighting, and sound. Objects cannot use appropriately, instead of a suitable control system. For example, if a room air conditioner has no control system or the volume of any music system cannot control, it would be difficult to use them. Therefore, it is essential having a control system with an electrical or electronic device. The control system of any electrical or electronic device is mainly of two kinds, manual and automatic control.

 

Manual Control - Here, devices are manually controlled, which means machines can turn on or off or control manually, consistent with their demands. For example, lighting up a bulb through a switch, turning on a motor by a starter, and decreasing or increasing the fan speed with a regulator. 

 

Automatic Control - With an Automatic control system, the device is automatically controlling certain circumstances or conditions. During the Automatic control, a device turns on or off within a selected time frame or controls it, like temperature or intensity of light. However, the manual controller is consolidated with every automatic control system, and there is the co-existence of two control systems (Automatic and Manual) collectively. For example, a system may start manually and stop automatically after attaining a specific state, including three different control operations, managing automatic machines or devices.

 

1. Relays, Timers, and Contractors

2. Micro-Controller

3. Programmable Logic Controller or PLC

 

Relays, Timers, and Contractors

With helping of a relay, timer, and contactor, a machine can control automatically and manage small logical operations efficiently. However, there are some disadvantages to using such a control system. It is very inconvenient and time-consuming, to change any logical operations, as relays, timers, and contactors interconnect with numerous wires. Also, it is unsuitable for extended and complex logical operations. We find this type of control system only with small automated machines, where small logical operations are functional. The following picture describes a typical automatic control system, including a relay and timer.

 

Micro-Controller

A micro-controller is a Special Purpose computer managed for a specific purpose only. Only some limited and special instructions are stored inside a microcontroller and directed to operate a selective machine or control system. For example, washing machines, and microwave ovens are typically controlled with micro-controllers. Applying a micro-controller-based control system is convenient but has some disadvantages. Users can not change the logical operation sequence of an automatic control mechanism if required. It only operates according to the instructions written inside its memory. Using a microcontroller is inconvenient for complex control operations, working with distinct elements, and requires integrating into different methods or modifying the control sequence. The following picture shows a typical microcontroller found with simple machinery and automatic controlling mechanisms.

Programmable Logic Controller or PLC

Introducing of Programmable Logic Controller or PLC can solve technical hitches with the earlier two types of control mechanisms. PLC is a typical digital controller, controlling some output elements, depending on the status of some Input elements and the program written inside it. It makes functional or controls some automatic processes. Here, the operation process or sequence of operation can change easily within a short period, executing this type of control system versatile and easily acceptable. Different PLCs are employed extensively for controlling several automatic control mechanisms. The following picture shows different PLCs, found with small control mechanisms. 

A PLC widely admitted where the operational sequence compelled to change in an Automatic control system. Also, with multiple logical operations with simple or complex machines, a PLC can manage efficiently. The size of a PLC usually depends on input and output handling capability, program size, and memory capacity. Companies like SIEMENS, FANUC, ABB, DELTA, OMRON, BOSCH, MITSUBISHI, and TOSHIBA are some leading manufacturers of different model PLCs, as per requirement. There are some differences with electronic circuitry inside the PLC for a separate make, but the working principles are roughly the same. However, there are some differences in hardware configurations and programming. For example, with small PLCs, CPUs with Power supply and Input / Output ports embedded in a single compact module, and extended PLCs, all elements work as separate modules, interconnected with cables. There is also some specific type of PLC, designed by PLC manufacturers, as per the user’s requirement. With CNC machines, PLC is typically embedded inside a CNC controller and PLC CPU or input/output modules cannot identify separately from outside. Here, all the discussions are confined to a discrete PLC, working independently. 

 

PLC is primarily segmented into two different elements the hardware part designed and fabricated by the PLC manufacturer and the program part written by PLC users, employing special software. PLC program always addresses company-wise specific software, which cannot accomplish in other PLCs. A Ready-made PLC of different companies is available, and SIEMENS and FANUC make PLCs are the most popular ones commonly found in modern machining industries. The following picture shows the common elements of a prefabricated PLC.