why are PID's so much more popular than PLC?

why are the PID based systems seemingly more popular than a PLC? (for the DIY crowd) is it that PID's are somewhat plug and play, while a PLC requires knowledge of how to create a program? he deems that a PLC would be a cheaper and more customizable option, but they surely don't seem to be as popular, so wondering what the reasons are.

Person 1

I would say the plug and play would be the answer. I would have loved to gone with a PLC system when I built my new control panel.

Person 2

PLC is probably more expensive and definitely more work if you are programming yourself. Buying a PID you basically enter the set point and I imagine you can enter tuning parameters (ie how fast or slow you want the heating element to heat the wort/mash etc..) I would go PID. I am currently using my electric stove, pretty rudimentary, right now until I have enough to invest in an electric system myself and will definitely get PID controllers.

Person 3

PID - Proportional Integral Derivative. A controller for controlling rate of change of a value with other outputs that it may control.

PLC - Programmable Logic Controller. A PLC is simulated relay logic controller. Typically a bank of discrete inputs and outputs; Digital or Analog, AC or DC.

A long time ago people used to use mechanical relays (switches) to hard wire logic (AND, OR, Latches, Timers-ON and Timers-OFF). Now its all done in ladder diagrams to simulate hard wiring.

I'm an automation engineer and have been away from this hands-on type of work for awhile. I am going to assume PID controllers are more popular because people don't want to create the code to do what a PID controller can do. While its possible to do on a PLC its easier to use PID Controller all alone or integrate it into a PLC.

While I don't have any recollection of the calculus for a PID I would use it as a module within a control system. Its easy, you have set points and limits to plug in and its all there. Somebody has done all the hard (logic)work for you. You just have to figure out the power supply, temp inputs and heating/cooling outputs.

Another example where you consider a PLC or another controller might be a frequency drive controller. This device controls the amount of voltage going to an AC Motor to change the rpm. (you might have it connected to a pump) It has canned routines for ramping 0-1725 rpm within a given time. It also can have dynamic braking to slow or stop an AC motor. The logic is all ready programmed into the controller. The user interface is built into the controller or it can be controlled by a PLC.

Now a days I think an industrial PLC might have a software PID module and hardware plug ins. Like I said I've been away from this for awhile.

A simple system with a single temp control purpose - stand alone PID controller with the 110 VAC power supply, thermo-couples, heating elements and etc.

A complex system with a multiple control features (like switches, multiple power requirements, AC and DC, thermo-couples, pH meters, lights, motors, solenoids, contacters, heating elements, and pumps) - use a PLC and a PID module.

Person 4

I am confident PID loops are easy in a PLC. It's just the hardware is much more expensive. As noted above, the PLC can do lots more, but if you don't use it, it's a waste.

Person 5

I've been designing/programming industrial controls (for the power plant industry) for the past 30 years. As mentioned when using PLC's the costs add up by adding automated valves, analog input modules, transmitters, etc. If you opt to add an HMI you have added cost of the HMI unit and associated software but gain the advantage of having more information available (status of pumps, valves, temperatures, etc.) and can have a menu system setup for different styles of beer.

What most people don't realize is the life cycle of PLC's and HMI's. By life cycle I am referring to when the manufacture no longer manufacture parts or provides support for the hardware. For HMI's the life cycle also includes the windows operating system used for windows based units as well as the programming software. PLC's typically have a 15 year life cycle and HMI's usually have a 7 year life cycle, HMI's have a shorter life cycle mainly due to the windows based hardware platform becomes obsolete which is also related to the software used to program the HMI. There are options to upgrade the HMI software, however if it doesn't support the hardware platform then you have to upgrade both.

Over the years I get involved with control upgrades for our systems but there are still a handful of relay based control systems that are still working after 75 years.

I plan on designing a control panel for my 2 BBL electric RIMS system and I am leaning on using the non-PID based controller  since I feel that a PID controller is overkill for the home brewery application. I also plan on using old fashioned switches, lights and pushbuttons for control. I however will use a variable frequency drive (VFD) to adjust the speed of my recirc pump. This also will allow me to feed the VFD with 220V single phase power and the VFD will provide the pump the needed 3-phase power.

PID Control systems for brewhouse and fermenting tanks

Our recommends:

(1)If you are expecting a fully automated control via PLC, it is not realistic as it is too much expensive.

-If you only use the PLC program and touch screen, but the valve is still manual, then the PLC will not show any advantage on reducing labor compared with the PID. Then PID is till recommended.

So if you really prefer the PLC, we recommend to use the pneumatic valves for the brewhouse.

(2)Set multi mashing temperatures and resting steps at one time (we also call this ‘temperature recipe storage’)

Comment:  This is suitable for this kind of mashing: mash in the kettle via direct heating rather than mashing via mixing with water.

(3) To display a more visual mashing process, and to look modern etc.

Comment: Some clients just expect to have a visual or modern image from the touch screen, then PLC with manual valve can be good enough

4)Is PLC good for cellar?

In the quote, the FV control panel is PID not PLC&touch screen.

If you would like the FV control panel to be touch screen too, then we need to combine the FV control panel with the brewhouse control panel.