PLC is Programmable Logic Controller and the Hard-Wired Control is a classical control..
PLCs are programmable as the name implies but hardwired control although it is more reliable but cannot be reprogrammed to change its behavior unless we make some rewiring modifications in the hardware.
hard wired means the logic circuitry is fixed and can't change without rewiring .
PLC is programmable ( which is in soft form ) we can mostly changes without changing in circuitry . much reliable quick .
Dear Abdeladim Moftah,
A Programmable Logic Controller, or PLC, is a ruggedized computer used for industrial automation. These controllers can automate a specific process, machine function, or even an entire production line. PLC executes the Control Instructions contained in the User's Programs. This program is stored in "nonvolatile" memory, meaning that the program will not be lost; also it can be modified if the technological process undergoes changes.
Hardwired control is a control mechanism that generates control signals by using an appropriate finite state machine (FSM). Micro-programmed control is a control mechanism that generates control signals by reading a memory called control storage (CS) that contains control signals. Also we can say that fixed logic circuits that correspond directly to the Boolean expressions are used to generate the control signals. · Hardwired control is the control hardware can be viewed as a state machine that changes from one state to another in every clock cycle, depending on the contents of the instruction register, the condition codes and the external inputs.
Best regards
Hard Wired Control is based on physically wiring feedback signals to acting devices commands in order to fulfill some kind of goal: For example, a temperature signal provides feedback to a burner controller to maintain the temperature of a boiler...
PLC control first "centralize" all the feedback signals and the commands signals to a controlling unit (funny enough, this is some kind of hard wiring too). The second big difference from Hard Wire control, is that the control decision is made through a Program which 'virtually' connects the feedback signals to the command signals.
In order to make it simple for electrician, at the time of inception of PLC, 20 century late 70's, a programming language was invented: Ladder Logic (LD), which mimics the hard wiring usually made into automation panels at that time.
LD was one of the first synchronous programming language (or reactive programming language)!
Ruggedize computer, as somebody mentioned, and LD are the two 'big' things of a PLC. Beside being ruggedized, a PLC is also very different from an IT computer concerning the Input/Output system: a PLC system is able to "process" many different kind of feedback signals (compared to a "regular" computer taking care of audio, video and digital communication) and to control many different kinds of actuators.
The three above criteria have been sufficiently discriminent for the inception of a niche market: the PLC market also known as the PAC market (Programmable Automation Control) which is roughly B€10 in size (2018).
PLCs do have something which may be hard to realize with hard wire logic - flexibility in creating, modifying and testing highly complex logic schemes. In cases where logic scheme requires remote signals to be wired, implementation and testing may be very hard to achieve. Contrary to hard wired logic, PLC have the possibility to communicate with each other using either proprietary or any of standard communication media and protocols (MOdbus, Profibus) to exchange information between (remote) PLCs. This highly reduces volume and complexity of plant wiring.
Hardwired control is a control mechanism that generates control signals by using an appropriate finite state machine (FSM). Microprogrammed (PLC) control is a control mechanism that generates control signals by reading a memory called a control storage (CS) that contains control signals.
One concept that I'd like to add to the discussion is the matter of complexity. Hard-wired control systems are well suited to applications that have limited complexity. The number of relays used in such a design is somewhat restricted due to space limitations, power limitations, and heat removal.
With PLC or PAC controls one can implement as many control 'relays' as memory will permit. If more control functions are required, multiple PLCs can be networked as mentioned previously expanding the capability. The final output relays in a PLC controlled system are generally smaller than those required for hard-wired control systems. With the reduction in wiring and the increased control functions available a much more complex application can be developed.
PLC is based on a Processor.
ie. discrete timings, responsiveness / real time capability is harder to achieve. Resolution issues regarding A/D conversion can occur. Complexity of control-algorithm can be chosen with less restrictions.
As the name say ,PLC is programibile controler is programabile ( changable on line ).Wheach mean he have development platform for design of aplicative program for logic design purpose . He have digital inputs outputs, as well as analog for handling of proces control . On the other side hard wire is design of controls with physicali wired controls with using of reley logic and usualy is implenmentedfor safety purpose ( if ESD is not implemented ) and for low logic problems where using of PLC is too expensive
I agree all the answers, and additionally, we can say that from point of view of process, where we have flexibility and a big amount of data it's used PLC, and in contrary conditions, it's used Hard-Wired Control
I agree all the answers.. However, hard-wired control which is based on electro-mechanical components (relays, contactaros, timers, etc) are still needed for some cases. Also, the electro-mechanical components are used with the PLC control because the contractors are used for starting the motors and not possible to connect them directly to the output modules of PLC, so in this case, the relays can be used to control the contactor by receiving the output signal from O/P module, on the other hand, the relay is working as an interface between the O/P module and the contactor.
The difference is very big as the manual control is done by a human being and the control using the plc is done by means of a program that was built to operate a specific system without boredom and no rest, in addition to that it can work in all environmental conditions that a person cannot work and control manually and can control a large number of The devices are parallel and this is not possible for manual control and it can be adapted to the environment as it is a program
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