Condensation & Outdoor Electronic Enclosures
Postado por Adelle Webber em
Condensation & Outdoor Electronic Enclosures
Water and electronic devices don’t mix well. Many electronic device manufacturers control the introduction of moisture by completely sealing the device to protect from any moisture entering the devices.
I now have bluetooth speakers that float in a pool and a cell phone that can take pictures underwater. The dynamics and challenges of outside industrial control systems housed in cabinets offer far greater challenges than sealed controls.
Preventing condensation in outdoor enclosures.
It is much more difficult to completely seal an electronic control enclosure from moisture and humidity. In my first job as an electronics control engineer, I help design temperature and power controls that were installed in enclosures for a wide variety of industries. The firm was small enough I not only designed the devices but tested them in the industrial enclosures, help install them at the industrial site, and would respond to troubleshoot the systems when there were problems.
These panels and controls were installed in glass, fiber, paper, Nuclear power, aluminum, chemical, textile, automotive, and coal mines.
The primary concern for most of the instrumentation and electronic controls was the enclosure temperature due to the ambient or heat generated by the electronics. Too much heat and the electronic components could fail or change their operating characteristics. The cabinets always had fans for moving air across the components and in some cases installed on the power components themselves. This was effective when the control panels were installed indoors on factory floors where there were some heating and cooling for employees and equipment.
My first challenge with high humidity and the humidity effect on the circuit boards was in the coal mines. The deep mines lacked air conditioning or dry air where the warm moist air caused humidity problems played out leading to short-circuiting with damaged electronic boards of the boards. Humidity and electronics don’t mix.
We would use different NEMA rated cabinets for applications where conditions warranted but for the most part very few needed outdoor enclosures where weather conditions were extreme. Ambient temperature in the factories high enough that condensation inside the electrical enclosures was seldom a problem.
The air does not to be warm and moist to cause the humidity effect to occur. Outside installations when temperatures fall below the dew point it becomes difficult to control condensate inside the outdoor cabinets.
When the temperature is lower than the dew point.
The point of condensation or dew point is when the air is cool enough it can no longer hold moisture. Humid air coming into contact with cooler surfaces of devices inside the cabinets there is a chance for water droplets to form on the devices. Thermal insulation can be used to prevent condensation in the cabinet and devices but it is difficult to control the humidity inside the cabinet if it needs outside air for ventilation.
Once the humidity level outside raises and moist air begins to circulate inside the cabinet the water droplets forming on the colder surfaces of the equipment can drop on exposed electrical components causing short circuits or build-up of moistures in displays.
If the relative humidity is 90% and the outside temperature is 86 degrees Fahrenheit the dew point is 82.7 degrees. Condensation can form on surfaces at that temperature of below. At 50 degrees outside the dew point for 70 percent humidity is about 40 degrees.
There are many parts of the US and the world where these conditions can exist and internal components and surfaces of electrical cabinets temperatures can be at the dew point and condensation will form.
Have you ever noticed condensation on the outside of your home or car windows when the inside temperature reaches the dew point? It can happen in summer or winter although less likely in winter when humidity is generally lower.
Controlling condensation inside outdoor electronic enclosures.
Outdoor enclosures installed where these types of conditions exist need thermal management systems to prevent the temperatures from falling below the dew point.
Where do these conditions exist? Many gas & oil facilities are in locations where the temperature and humidity vary considerably with the seasons. Texas, northern Africa, the Middle East, are a few. My first experience was with control systems mounted outside along the fertilizer and plastic processing lines in factories located in Basra Province or Iraq.
It never occurred to me that those locations had temperature ranges from 125 F to 25 F. These temperatures included a wide range of humidity and dew points. It was impossible to use NEMA 12 enclosures even with the chemical hazards.
Heaters are often used to keep the humidity inside the cabinet lower than the dew point. These heaters are mounted at the bottom of the cabinet where nature convection carries the heat through the cabinet.
Sometimes a fan is used to ensure the heat is evenly dispersed to all surfaces. Point surface conduction heaters can also be used on selected components that might be more susceptible to condensation forming on their surfaces.
What can be used to sense humidity and control the condensation?
A humidity sensor (or hydrostat) senses the moisture in the air. The humidity sensor, hygrostat measures, and reports both moisture and air temperature. The ratio of moisture in the air to the highest amount of moisture at a particular air temperature is called relative humidity. Relative humidity becomes an important factor when combating condensation.
When the sensor senses the moisture is getting too high relative to the temperature it can turn on heating elements to raise the temperature. Raising the temperature decreases the relative humidity in the cabinet and reduces the chance for condensation. These types of control loops can be found in your household refrigerator preventing condensation from forming on the inside walls and food. Typical household freezers don’t have condensation protection due to the lower temperature and you will find ice (condensation) on the surfaces of the packages inside.
The same concept occurs inside outdoor electronic cabinets such as ATMs, kiosks, traffic light controls, industrial applications like oil & gas, windmills, and others installed in remote locations.
Overview of what controls and devices are available from DBK USA.
DBK USA has available a wide range of controls and PTC devices to help you prevent condensation in your outdoor enclosures. View or product section of the website or follow the links below to find out more about the individual devices.