Taking Control Using Control Systems

Control systems are common place in almost every industry and market. They are used in our microwaves, televisions, ovens, toasters and refrigerators, which are some of the simple uses of control systems, but of course there are neater applications, like in our beloved Star Wars characters R2-D2 and CP3O, in aerospace navigation and airplanes, as well as in rockets and medical surgical robots. But whether it is practical, or just for fun, any control set-up involves three key elements.

The Parts of a Control System

Sensors

Sensors are the items we place all over the place in order to get information. For use in our surroundings, this could be photon sensors or humidity sensors, and on our bodies this could be our eyes and ears, or our sense of touch.

Actuators

Actuators are the part of the system that get all the action (pun intended). For example, these range from ballasts and CO₂ burners, or they could be motors in your car when cruise control is activated, or the muscles in your arm when you swing away from a bug bite.

Controllers

Controllers are quite literally the brain of the entire operation. Controllers take the input data from sensors and put it through a control algorithm that then computes the output and sets the entire system that is being controlled into action to combat whatever disturbance was sensed. For our bodies, obviously this is our brain. For our growrooms, things are a little less complex and the controller becomes our microcomputers, or our fellow gardeners.

Control Schemes

There is a whole other science happening outside of putting together equipment and tools to create a control system, and this is the science of algorithms. These mathematical formulas act as the sorcery or the magic that makes our entire systems work. Whenever we have a sensor that lets us know that something has changed, that signal is converted into a number or string of numbers that flows into the controller.

The controller has an algorithm that takes this number and checks how the system needs to change to get rid of this sensed trouble. Once it is done it sends it back out into the system and towards the actuator. The actuator then acts on the new signal to correct the disturbance and then the sensor should read its set-point before the disturbance.

This is just one cycle of what the control system goes through, and it is literally happening as many times as 100,000,000 times a second in things like aircraft homing missiles, and in our brains. Controllers for hydroponics do it a couple of times a second to (up to 10,000) because the need for nanosecond accuracy is just a bit much for our plants.

Equipment for Controlling Different Growroom Parameters

In a growroom the main variables that need to be controlled are CO₂, lighting, humidity, root-zone temperature, greenhouse or growroom temperature, nutrients and pH levels in our growing solution. In order to control these we have to set up sensors for each of these. The standard sensors are things like pH sensors or TDS/EC sensors and these let us know how our growing solution is doing.

As for lighting, we can use a standard photon flux meter or a spectrometer if we really want to get into the complexity of tailoring light so that our plants can think they’re in Africa during one part of a grow and in the South American jungle in another. Other equipment that is needed is a little bit harder to find, but for things like humidity and CO ₂ we use chemically reactive sensors that give us electrical signals that change with concentration to let us know how our growroom variables are doing.

Lighting

Lighting in a growroom is among the simplest things to control because all we really need to do is turn lights on or off to change the total light period and plan our lighting according to what stage plants are in during their lifecycle. For this set-up we really just need a controller. Our actuator is a relay and the algorithm we use is a simple boom-boom control system that turns the system on or off based on the time inputs we give it.

Humidity

A little more complex than light, we have to be able to control the amount of water in the air around our growroom and this is no simple task. For a large growroom there can be huge differences in the amount of water in the air from one side of the room to another. If you can imagine a wave of mist moving from one side of the room to another, you can imagine that if the system only had one sensor on one side of the room, the humidity could be perfect on one side and absolutely dry on another. This sort of variable needs multiple sensors across the room if a large growroom is involved.

CO­2

Like humidity, this variable is hard to control because of the volatility of gasses and the fact that unless vent fans or channels to direct flow are used, it is going to be very difficult to get even coverage throughout a growroom or a greenhouse. For this reason we usually put our sensor far from our actuator and in many cases in a centralized or opposing area of the room so that if we are only using one sensor we know that it is giving us a really accurate reading of where the entire room is at.

Nutrients and pH

These are the most complex variables in our plants grow cycle. This is the food that we give our plants to grow and we really need to take a visit back to Goldilocks to appreciate why. First off, too little nutrients will starve our plants so they won’t be able to grow. Second, too many nutrients and our plants will not be able to eat them and grow. But, when we make sure that pH and nutrients are just right for growth and made appropriate for that stage in the growth cycle, then we have a happy plant that grows quick, which is just right!

A final note

All in all, control systems are a part of the indoor gardening industry that make our lives easier and allow us to watch ourselves get bigger grows and do more with our time and money than allow error to ruin our plants. Control systems are an emerging tool for all growers and it is recommended that growers keep up with the pace of these evolving products, which are quickly becoming essential.