PLC (Programmable logic controller) vs PID - what are the differences?

Totally different sorts of things. A PLC is s general purpose controller. Often these are used in mechanized automation, but it very broad in application. PID usually refers to a form of closed-loop control; named for the terms Proportional, Integral and Derivative. PID controllers are often used in temperature control. It's a fairly general term as it has been implemented in hundreds of different forms. A PID loop can be implemented on a PLC.

P.I.D. = Proportional - Integral - Derivative

It is a mathematical calculation that can control many things.

Temperature is the most common that you will find.

I had helped develop a P.I.D. proportioning valve using Labview.

Very time consuming when starting from scratch!

In the end it worked great!

PLC = Programmable logic control. As it's name suggests it controls on the basis of pre-programmed logic.

PID has already been answered by Bjorn and Kid. They are different.

My dear cooleagues, In PLC You do have both open-loop and closed-loop control systems. So, You can control sequential processes as well as to apply PID control by means of analog modules of PLC!

Regards,

Ljubomir Jacic

PLC stand for Programmable logic controller. PLC can be used as remote terminal unit. PLC also used for interfacing with SCADA system. I am also agree with Ljubomir Jacić.

PLC somehow relates to hardware. PID is one of the simplest example of controller for feedback loop, based on 3 different kind of action on the error (proportional, integral and derivative). One can implement PID using a PLC, or with it's favourite hardware. That's all.

Dario is correct!

You will program a PID control into the PLC.

The hardware is the PLC, and the software is the PID.

Chitta:

What are you needing to do using these?

thanks for spending your valuable time. suppose i want to control the level and temperature of a tank. so in this case which will be more help to achieve my set point.

1. two pid contoller with labview

2. pid contoller with PLC

You may want to look into an Omega temperature controller, before trying to program your own logic, as it is very time consuming.

Then using labview, you can control outputs for solenoids to handle your Level.

Labview has great charts to monitor everything, then if you do have the time to spend on it, will do just fine but you may need some reference on building the PID inside your main loop.

PID is one type of controller, which can be implemented using several techniques. PLC is a general term for a controller which is programmable. PID can be implemented on PLC. Several controllers can be implemented in PLC.

I think it is just like windows installed in your PC. So, PID is like windows and PLC is like your PC.

PLC is a digital controller while PID is analog controller

PID can also be implemented digitally.

PLC is mainly used in automation plants as a remote terminal unit.

PID is not a controller.....

It is actually a mathematical equation that is implemented through a PLC.

Copied from:

PID Control:

The third controller type provides proportional with integral and derivative control, or PID. This controller combines proportional control with two additional adjustments, which helps the unit automatically compensate for changes in the system. These adjustments, integral and derivative, are expressed in time-based units; they are also referred to by their reciprocals, RESET and RATE, respectively. The proportional, integral and derivative terms must be individually adjusted or "tuned" to a particular system using trial and error. It provides the most accurate and stable control of the three controller types, and is best used in systems which have a relatively small mass, those which react quickly to changes in the energy added to the process. It is recommended in systems where the load changes often and the controller is expected to compensate automatically due to frequent changes in setpoint, the amount of energy available, or the mass to be controlled.

OMEGA offers a number of controllers that automatically tune themselves. These are known as autotune controllers.

(1) I agree with Bjorn Burton's comments.

PID is proportional–integral–derivative controller. It uses a feedback loop to correct the difference between the measured system output and a desired setpoint.

PLC is programmable logic controller. It is used to control a machine or interlock different equipment. Early PLCs were designed to replace relay logic systems. These PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic.

Most modern PID controllers in industry are implemented in PLCs or as a panel-mounted digital controller.

(2) Quote Chitta Behera's question "suppose i want to control the level and temperature of a tank. so in this case which will be more help to achieve my set point."

 

(a) You can implement "1. two pid contoller with Labview". One PID controller to control the level, and one PID controller to control the temperature.

The following two papers implemented one PID controller using Labview to control the level of a tank. 

WK Ho, Y Hong, A Hansson, H Hjalmarsson, and JW Deng, "Relay auto-tuning of PID controllers using iterative feedback tuning," Automatica 39 (1), January 2003, pp. 149-157.

 https://www.researchgate.net/publication/223504459_Relay_auto-tuning_of_PID_controllers_using_iterative_feedback_tuning

W.K. Ho, T.H. Lee, H.P. Han, and Y. Hong, "Self-Tuning IMC-PID Control with Interval Gain and Phase Margin Assignment," IEEE Transactions on Control Systems Technology, 9(3), May 2001, pp. 535-541.

 (b) You can also implement "2. pid contoller with PLC."

Either Labview or PLC would work well to control the level and temperature of a tank. The choice depends on your available experimental resource on hand.

I agree with Kid Cowles's comment "Labview has a chassis that can monitor temperature, and another module for relays, and other sensors."

I agree with Alessandro Tasora's suggestion "you buy a cheap PLC and implement the PID loop on it" if currently you does not have either Labview or PLC on hand. PLC is much cheaper than Labview for your implementation to control the level and temperature of a tank.

 (3)  Discussions on control system design

"What are trends in control theory and its applications in physical systems (from a research point of view)?"

Chitta:

Do you need to use labview to do this operation?

Or can you just use off the shelf controllers to take care of your:

1. Temperature

2. Level control

Labview has a chassis that can monitor temperature, and another module for relays, and other sensors.

You can build anything you can possible desire! If need be I can find the chassis and modules that I have used to point you in the right direction.

Many years ago people implemented PIDs via analog hardware, but nowadays most PID control loops are implemented as software algorithms in digital devices. A PLC is only a special case of such devices. That is, you can have one (or more) PID running in a PLC box, or in an industrial PC, or in a SOC system-on-chip like ARM microcontrollers, or in very cheap microcontrollers like Arduino or PIC 8-bit processors, or on a CompactRIO box with sophisticated real-time operating systems, etc... It is up to you. But if you need a very simple control, that does not need high bandwidth, my suggestion is that you buy a cheap PLC and implement the PID loop on it - depending on the brand of the PLC you'll find many programming examples.

Chitta: Labview is a tool which can be used to generate control signal like PID controlled o/p. However, in any case there is a need of digital/analog device to transform computer programmed signal from Labview. PLC is one of the digital device can be programmed to behave according to PID logic.

Now you can make a PID algorithms in PLC . In addition , you can use PID controller card in your PLC racks. I am agree that PID was analog controller . Now it is fully digital. 

if I need to use PID controller in the system , I will use it in PLC program.

But sometimes, if your process is very important means dangerous,you need extra safety logics. In this case you will need to use safety PLC s. In this focus , you can think to use PID controller which is independent from PLC systems.