Industrial Air Dryer Designs Demand a Keen Eye for Safety

Created: March 20, 2018
Updated: September 25, 2020
Dryer graphic with rotation arrows

Early in my school days, I was lazy and forgetful. I would procrastinate on everything, including washing my school shoes. Pressed for time, I often dried my shoes under the radiator coil of an old-school refrigerator. Of course, that didn’t spare me from an earful of mom’s scolding.

In one of my first industrial electronics designs, I did more than drying shoes. I designed an intelligent air dryer controller for a local milk powder processing plant. Being new to manufacturing, and specifically the industrial air dryer industry, I learned that safety is the topmost priority in hardware design.

By using the right software, and through continually reminding yourself of the challenges and constraints that you’re working with when designing hardware, you can also build an air dryer or any hardware you need for your electronics environment.

What is an Industrial Air Dryer?

In the typical air that we breathe, there is a percentage of water vapor that can corrode or affect manufacturing processes. It can also cause contamination when food processing is involved. An industrial air dryer ensures that the air is free of vapor before entering manufacturing areas.

A type of industrial dryer is the regenerative desiccant dryers where desiccant beads are used to adsorb the moisture in the air. These are performed by a couple of towers where the air is in one of the towers while the desiccants are being regenerated in the other. This takes place for a period of time before the air is switched to the second tower.

Designing an Industrial Air Dryer Controller

For hardware designers who’re used to designing commercial electronics involving complex algorithms, an industrial air dryer controller may appear simple. After all, it’s nothing but a set of relay outputs and analog inputs connected to a microcontroller. However, underestimating the hidden concerns in air dryer design can lead to safety risks.

Industrial worker with safety equipment and signs
Safety is the priority in industrial air dryer controller design

Controlling The Valves

There are at least four valves that need to be controlled by your hardware. From the perspective of a designer, these are simple relay outputs. But what a designer must understand is that the pressure of air in the tower is very high and any mistakes in switching the valves can lead to some of the equipment exploding.

There are two critical of relay output design that demands your full attention. One is when the airflow is switched from one tower to another. It is important that the valve for the second tower is opened before the first one is closed. This is to prevent the sudden spike in air pressure when the air has nowhere to flow.

While hardware designers have little control of the firmware algorithm, they can ensure that the relay signals are protected from any electrical interference. Besides routing the signals far from high-frequency tracks, it is best to ensure that relay signals are pulled up or down so the valves are open when microcontrollers enter an undefined state, even for a short period.

Acquiring Accurate Parameter Values

There are two important parameters for an industrial air dryer. The controller needs to regularly monitor both the pressure and dew point when the air is being adsorbed at either tower. The air pressure in a tower should not exceed its rated maximum value when the regenerative valve is being closed. A functional air dryer should have the dew point dropping to the desired value during the adsorption process.

These values are usually monitored by industrial sensors, while their readings are acquired by the controller thorough Analog to Digital Conversion (ADC). Working with analog signals in an industrial environment increases challenges for a designer. The electrical environment of a factory is often notorious for causing electrical interference.

It is important to follow the best practices of analog design in your PCB. The tracks need to be separated from high-speed digital or power tracks and a separate ground plane needs to be placed under analog components to provide stable sensor readings. You do not want the controller to be oblivious to abnormal increases in air pressure.

Pressure gauge and sensor values meter
Expect nothing but high pressure with an industrial air dryer

Perfecting the Industrial Air Dryer Controller Design Process

Designing an industrial air dryer that works in the lab is child’s play for most designers. But designing one that is safe and robust requires near perfectionism. A good designer must be prepared to restart from scratch, if needed, to address potential issues like electrical interference and spikes in air pressure. 

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