When it comes to different types of kiln controllers, there are two broad categories you need to keep in mind: process controllers and limit controllers. These two controllers have very different roles and functionalities that will impact how you use your kiln or heat treat oven.
So, what’s the difference?
Process Controllers vs Limit Controllers: Function & Use Cases
If you use an at home kiln or a studio kiln, chances are you’re more familiar with a process controller. Process controllers, also known as programmable digital controllers, automatically adjust kiln temperature to execute kiln firing schedules with very little user involvement.
These controllers use sensors to measure chamber temperature and then dynamically adjust output to the elements to make sure the kiln progresses through the desired setpoints.
Limit controllers, on the other hand, don’t directly execute firing schedules. Instead, they monitor kiln temperature and ensure that the kiln automatically shuts off if the kiln exceeds a specified temperature.
Also known as high limit or safety limit controllers, limit controllers are more commonly used with ICS control systems, industrial kilns, and manual kilns.
Here’s another way to think about it: Process controllers execute processes; limit controllers enforce limits. Simple, right?
Primary vs Secondary Kiln Control Methods
Another difference between limit controllers and process controllers is whether or not you can use them as your primary kiln control method.
Process controllers are a primary kiln control method. That means that you can use them to fully control every operation of your kiln.
Limit controllers, while not usually suitable to be the primary control method, are an important part of kiln safety and can protect you, your equipment, and your property in the case of relay or system failure.
If I Already Have a Process Controller Why Would I Need a Limit Controller?
If you’re reading this article and you already have a process controller, you might be asking: Why would I need a limit controller?
The answer? Safety.
Even though advanced process controllers, such as the TAP II and TAP II Pro, provide max temperature safety shutoff in case of relay failure, redundancy is the key to safety. Safety limit controllers such as TAP Monitor add an additional layer of safety. When installed and wired to a redundant safety relay, TAP Monitor will automatically shut off your kiln if it exceeds a specified temperature – even if your primary relay fails.
Benefits of TAP Monitor Limit Controller
TAP Monitor is an advanced, user-friendly kiln limit controller and pyrometric device that can be paired with any manual or automatic kiln controller to provide safety shutoff and remote temperature monitoring.
Available as a plug-and-play standalone pyrometer or as a set of configurable components for DIY installs and oven builds, TAP Monitor gives ceramicists, potters, glass artists, and knifemakers the ability to:
- Wire TAP Monitor to a safety relay to provide redundant safety shutoff.
- Precisely monitor the temperature of their kiln, oven, or forge via the TAP Kiln Control Mobile app.
- View digital pyrometric readouts from any manually controlled kiln, including remote readouts via TAP Kiln Control Mobile when TAP Monitor is connected to a local network.
- Easy installation for precise, real-time digital temperature readings to their manual kiln or oven.
- Pair TAP Monitor with their existing automatically or manually controlled kiln for remote monitoring.
Explore Kiln Control Solutions by SDS Industries
In addition to the TAP Monitor Limit Controller, the TAP Ecosystem includes a variety of programmable kiln controllers that give artists complete control of their kilns. The TAP II [Single Zone] and TAP II Pro [Multi-Zone] Controllers by SDS Industries provide users the most advanced, precise, and easy-to-use programmable digital kiln controllers on the market today. With responsive touchscreen controls, an intuitive graphical UI, and integration with the TAP Kiln Control Mobile app, TAP Kiln Controllers can pair with any relay-controlled kiln or oven.
We invite you to explore our selection of programmable kiln controllers, pyrometers, standalones, and conversion kits on our online store. You can also purchase TAP Digital Controllers or TAP Controlled Kilns and Heat Treat Ovens through one of the following distributors:
- Evenheat
- Hot Shot Oven & Kiln
- Paragon Kilns
- Mobile Glassblowing Studios, LLC
- Jen-Ken Kilns
- Kiln Frog
- Sheffield Pottery
- Delphi Glass
Process Controllers vs Limit Controllers FAQ
Do I need a limit controller for my at home kiln or oven?
For at home kilns or heat treat ovens – or even most studio kilns – you don’t technically need a limit controller. In fact, your process controller should already include max temperature shutoff that enforces limits when your kiln exceeds a predefined temperature.
However, adding a limit controller in addition to your primary kiln controller has multiple benefits:
- Enhanced Safety: Your process controller only provides safety shutoff if your primary kiln relay is working. If that relay fails and gets stuck in the on position, your kiln will keep heating up indefinitely. A limit controller uses a secondary safety relay, ensuring that your kiln safely shuts off even if your primary relay fails.
- Remote Temperature Monitoring: Most kiln controllers don’t provide remote temperature monitoring (it’s one of the features that sets TAP apart). Using an advanced limit controller like TAP Monitor lets you easily add remote monitoring and push notifications to any electric kiln or oven build with any type of kiln controller – even if you’re still using a kiln sitter!
- Temperature Verification: Some artists still use pyrometric cones to verify that their thermocouples and elements are working properly and that their kiln is consistently reaching the right firing temperatures. A limit controller provides that verification without having to purchase pyrometric cones or wait around to watch when they melt.
If you’re interested in adding these benefits to your kiln or oven build, we encourage you to check out TAP Monitor!
What sets TAP apart from process controllers by other kiln controller manufacturers?
If you’re in the market for a process controller, we encourage you to check out TAP. We designed TAP from the ground up to be the most advanced, precise, and easy-to-use kiln controller on the market today – whether you’re controlling your kiln from its touchscreen or remotely from your smartphone or tablet.
Compared to other temperature controller manufacturers, TAP Kiln Controllers provide a host of benefits that make life easier for artists:
- Program your kiln faster, reduce eyestrain, and spend less time reading user manuals with intuitive touchscreen controls and a graphical UI that contains all the information you need at all times.
- Save, name, and execute unlimited firing schedules with unlimited steps – so you can consistently execute the schedules you need without having to shuffle through your kiln notebook or recreate schedules.
- Multitask more effectively and enjoy more peace of mind with real-time temperature monitoring, push notification alerts, and true end-to-end remote control through your smartphone or tablet.
- Enjoy maximum precision with PID (“Proportional Integral Derivative”) control algorithms that monitor chamber temperatures and dynamically adjust outputs to ensure your kiln adheres as closely to the programmed schedule as possible.
- Easily integrate your controller with the industry’s – by far – highest rated kiln control app and the only one that offers remote kiln control.
The TAP Ecosystem is designed to work with virtually any electric kiln or oven and has options for a variety of functions and budgets – so that you can find the kiln controller that’s perfect for you!
How are limit controllers utilized on industrial control systems?
While this article deals more specifically with limit controllers for temperature control, industrial control systems use limit controllers to enforce limits for a variety of setpoints that extend beyond temperature.
These include:
- Temperature: Ovens or machinery overheat or underheat.
- Pressure: Too much or too little pressure is built up in a control system.
- Electrical: Too much or too little power is being delivered throughout a control system.
- Mechanical/Physical Processes: The physical movement of machinery exceeds specified ranges, jeopardizing accuracy and flexibility.
- Sound Control: Processes result in sound that exceeds specified volumes.
- Accuracy or Error Limits: Ensuring the accuracy and consistency of outputs.
As you can see, different types of limit controllers play a role in virtually every type of manufacturing or industrial process. To learn more about ICS controllers and industrial control systems, check out ICS Controllers for Industrial Control Systems.
