What Is Closed-Loop Automation?


During Networking Field Day 22 last week, a lot the questions that were directed at the presenters had to do with their automation systems. One term kept coming up that I was embarrassed to admit that I’d never heard of. Closed-loop automation is the end goal for these systems. But what is closed-loop automation? And why is it so important. I decided to do a little research and find out.

Open Up

To understand closed-loop systems, you have to understand open-loop systems first. Thankfully, those are really simple. Open-loop systems are those where the output isn’t directly affected by the control actions of the system. It’s a system where you’re going to get the output no matter how you control it. The easiest example is a clothes dryer. There are a multitude of settings that you can choose for a clothes dryer, including the timing of the cycle. But no matter what, the dryer will stop at the end of the cycle. There’s no sensor in a basic clothes dryer that senses the moisture level of the clothes and acts accordingly.

Open-loop systems are stable and consistent. Every time you turn on the dryer, it will run until it finishes. There’s no variable in the system that will change that. Aside from system failure, it’s going to run exactly 30 minutes every time it’s set to that cycle. It’s also not going to run unless you set the cycle. As my family will tell you, putting clothes in the dryer and not setting it will not result in magic happening.

Close It Off

In contrast, closed-loop systems have outputs that are dependent upon the control function of the system. If the control function requires something change in the system to achieve the desired output then it will change that thing to get there.

The most classic example of a closed-loop system is the HVAC system in your house. The control function is the thermostat. If you want the temperature in your house to be 70 degrees Fahrenheit (21 degrees C), you set the thermostat and let the system take care of things. If the temperature falls below the required setting, the heating unit will turn on and bring the temperature up to the required level before shutting off. In the summertime, rising above the temperature setting will cause the air conditioning compressor to kick on and cool things down.

Closed loop systems are great because you set them and forget them. Unlike the dryer example above I can set my thermostat and it will run even if I forget to go turn on the heater/AC. But they’re also more complicated to troubleshoot and figure out. As someone with very little practical knowledge of the operation of HVAC it’s rough to figure out if it’s the thermostat or the unit or some other relay somewhere that’s causing your house to be too warm or too cold.

Closed loop systems can also take more inputs given the right control settings. Using the same A/C example, I upgraded my thermostat from a basic model to one from Ecobee. Once I got it installed I had a lot of extra control over what I could do with it. For example, I could now have the settings in the house run based on time-of-day instead of just one basic setting all the time. If I wanted it colder at night I could tell the system to look at the time and change the setting until it was sunrise. I could also tell it to look for me to be home (using geolocation) and raise and lower the temperature if my geotoken, in this case my phone, wasn’t in the area. The possibilities are endless because the system is driven by those inputs.

Automatic for the Non-people

Let’s extend the idea of closed-loop systems to network automation. Now, you can make a system (the network) behave a certain way based on inputs to the control functions. This is a massive change from the steady-state that we’ve worked years to achieve. The system can now react to changes in state or inputs. Massive file transfer activity being done between two branch locations? Closed-loop automation can reprogram the edge SD-WAN gateways to implement QoS policies based on the traffic types to preserve bandwidth for voice calls or critical application traffic. When the transfers are done the system can clean up the policies.

Because closed-loop automation can do a wide variety of actions based on inputs, data becomes super valuable. The information your system is providing as feedback can create more stable results. Open-loop systems are super stable because they are incapable of change. They also run every time someone tells them to run. They require intervention. Closed-loop systems are capable of running without the need for people based solely on the data you get from the system. But they also have issues because bad data or inputs can cause the system to react in strange ways. For example, if the thermostat in a house is placed in direct sunlight or has an error that causes it to think the house is 90 degrees, the A/C compressor may kick on even if the house temperature is far, far below that. Data has to be correct for the system to work as intended.


Tom’s Take

The promise of closed-loop automation is exciting. The ability for the network to run without our help is music to my ears. But it also means we have to be more diligent about keeping the control functions of the system working properly with the correct data inputs. It also means we need to monitor the control system outputs to head off problems before they can impact the reliability of the system. I can’t wait to see how we continue to close the loop and create better, more responsive systems in the future.

1 thought on “What Is Closed-Loop Automation?

  1. Pingback: What Is Closed-Loop Automation? - Tech Field Day

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