Articles

[Manufacturing] - Humidity Chambers (part 2)

May 17, 2022

4. Construction of a Humidity Chamber

4.1. Walls

The construction of the bulkheads of a humidity chamber is an essential part of the design. A key element in product testing is to ensure that the air produced is not contaminated by the surrounding environment. All humidity chambers are double-walled and can be made modular or welded. The welded design is preferred as it gives better sealing to the case.

4.2. Doors

To preserve and contain the environment in the humid chamber, the doors are double-walled and fitted with heavy duty hinges with a mechanism that completely seals the chamber when closed. Door construction is essential to ensure chamber integrity and prevent any potential ambient contaminants that could skew test results.

4.3. Controllers

The control mechanism for humidity chambers is a proportional integral derivative (PID) controller, which provides continuous modulated data and error values or the difference between the setpoint and measured process variable. The controller takes in the accumulated information and makes automatic corrections in accordance with the proportional, integral, and derivative terms.

A PID instantly and automatically makes corrections to the controlled function. If the particulate humidity falls below the desired setting, the controller makes the necessary adjustments to keep the ratio constant.

4.4. Temperature

The heat for a humidity chamber is provided by a direct heating coil or wire, which evenly distributes heat to all parts of the chamber. When a humidity chamber is designed, its size determines the heat range. Large walk-in chambers have a highly complex heating system connected to the air supply, while smaller chambers are able to use a more direct heating method.

The heating elements are normally encased in ceramic. The calculation of the required temperature is computed by the control system once it has been programmed with the parameters for the items of the testing.

4.5. Air Supply

The purpose of the air supply system is to circulate the humidified air in the inner chamber and consists of a circulating motor, circulating wheel or fan, and air duct system. The air supply system is designed to pull in air from the surrounding environment and distribute the humidified air in the chamber.

4.6. Humidity System

There isn‘t one single way that the humidity in a humidity chamber is produced. Some chambers have a water tank that is heated to produce steam that is vented into the chamber, while other systems have spray nozzles. The heating system has water and vapor controls to meet the required international standards for humidity chambers. In each of the systems, there is an overflow control to avoid having the chamber having too much moisture.

4.7. Materials

One of the key requirements of a humidity chamber is durability. They are constructed of thick and durable metal sheets that are designed for wear resistance of the highest quality steel. The majority of test chambers are made with a welded steel frame on the exterior and a stainless steel interior liner. They have fiberglass or silicone insulation with a 0.25k factor.

To add to the life of a test chamber, the metals are powder coated and painted for corrosion resistance and ease of cleaning. A key feature of humidity chambers is their double wall seal that ensures the quality and accuracy of atmospheric tests.

5. Types of Humidity Chambers

The types and designs of humidity chambers vary according to the type of testing to be completed and the size of the parts. There are test chambers that can fit on a shelf to test the effects of humidity on small parts. On the other hand, walk in and drive in chambers are large enough for a car and large computing systems.

In most cases, the type of chamber, that a customer purchases, is designed to fit the specific needs of the customer. Each industry has requirements and types of data that are needed to ascertain the quality of their products, which necessitates producers to design and manufacture a wide variety of test chambers.

Regardless of the specific designs and varying sizes, there are certain criteria that are applicable to all forms of test chambers.

Types of Humidity Chambers

5.1.  Benchtop Humidity Chambers

Benchtop test chambers are a cost effective method for the testing of products. They are used for testing smaller components such as electronics, sensors, or cell phones. They are made for research labs or small businesses. Benchtop test chambers vary in size from 0.89 cubic feet up to 5.5 cubic feet. They can have the same basic features as larger units in a more compact size.

5.2. Reach-In Humidity Chambers

Reach-in test chambers have a smaller footprint than larger models with similar versatility as benchtop models. They come in a vertical configuration that allows for easy access but are completely sealed during testing. Reach-in models come in several sizes to match the available space. They are designed with casters or wheels for convenience.

5.3. Walk-In Humidity Chambers

When humidity chambers are large enough to be entered, they are specifically designed to accommodate location and temperature requirements. “walk-in” test chambers can be built modularly, where they are installed as a single unit on site depending on customer needs. In the case of “walk-in” humidity chambers the equipment requires a very complex steam flow and distribution system to ensure uniformity of the desired conditions. The “walk-in” type humidity chamber is widely used by automotive, electronics and battery manufacturers..

5.4. Drive-In Humidity Chambers

The primary purpose of “drive-in” test chambers is to test vehicles under a number of atmospheric and environmental conditions to determine their lifespan and durability. Just like the “walk-in” booth, the “drive-in” booth had to be designed to meet the needs of customers, mainly automotive companies. Drive-in chambers are programmed to test all movable parts of the vehicle, including doors, windows, switches, lights and knobs. One of the essential features of the transmission chamber is to test the endurance of the engine in a variety of climates..

5.5. Scientific Testing Chambers

Science test chambers are like any other type of test chamber and are used to create small environments. The purpose of science laboratories is to examine samples for potential flaws or problems. The data collected is crucial for the development of future products for the food science, pharmaceutical and electronics industries. Types of test methods range from simple high temperature to excessive humidity. The primary purpose of science laboratories is to complete the testing of specimens on-site rather than sending them to laboratories. Laboratory test chambers are used to create a variety of environmental conditions such as corrosion testing and for biological research.

6. How to Choose a Humidity

6.1. Space

The space the company has available is a guiding factor when making a decision to purchase a test chamber. Chamber manufacturers work with their customers to ensure that the chamber they purchase fits the space available and the customer's needs.

6.2. Temperature

Temperature is an essential part of a humidity chamber since it is necessary to create the vapors and humidity. The majority of chambers are capable of reaching temperatures of 200° C. The factor that can influence the range of temperatures to be achieved is the construction of the chamber and its stability.

6.3. Water Supply

The design of the test chamber determines the amount of water needed to create humidity. As important as this is, it is also critical that there be some form of drainage or method for removing water at the end of a test cycle. The location where the chamber will be placed should be designed for a water supply and proper drainage.

6.4. Time

Every humidity chamber has a different ramp-up and pull-down time. When planning to purchase a unit, it is important to consult with researchers to determine the time frame they require to complete the collection of data. Long ramp-up times can delay tests and may produce tainted results depending on the item to be tested. Manufacturers are careful to examine this factor with their customers to ensure the unit meets the customer‘s requirements.

6.5. Relative Humidity (RH)

Most humidity chambers have an RH factor between 20% to 98%. This consideration is determined by how the product is to be tested and what data is required. In the majority of cases, this is planned long before contacting a test chamber manufacturer.

6.6. Controller

The decision for the type of controller is a central factor when purchasing a humidity chamber. The features that offer the best results are controllers with a microprocessor, which can be LED, LCD, or touch LCD. An RH display comes with all humidity chambers as well as a solid state RH sensor.

7. Weaknesses Humidity Chambers Test

Coatings

Many products have coatings to protect them from harsh and damaging atmospheric conditions. Humidity chambers place coated products in the harshest of environments. The results of the tests can cause cracking in the coating, expansion, contraction, moisture ingress, corrosion, and abrasions.

Fogging

Sealed units that have a window, viewport, or windshield are tested for moisture seepage between the layers. Since these products are exposed to rapid temperature changes, they are normally put through tests that rapidly raise and lower the temperature and humidity. If the product fogs, it is an indication of its potential for failure and poor quality.

Tightness

The two most damaging atmospheric conditions are temperature and moisture. To ensure that a product is not susceptible to water ingress and has a tight seal, it is subjected to several cycles of humidity with varying moisture content. The failures that emerge from the testing is leakage and water droplets or collecting.

Mechanical Failures

Atmospheric conditions create a great deal of stress on a product as it passes through a variety of climatic conditions. Humidity chambers are able to create any of the types of conditions that can cause the mechanism of a product to fail. In essence, the test of mechanical components and their proper function is the main concern for manufactures especially in relation to electronics and microcircuitry.

8. Humidity Chamber Regulations and Standards

There is an endless number of agencies, organizations, committees, and governmental regulations that govern humidity chambers. The more stringent regulations are related to pharmaceuticals, medical suppliers, and food production. A few of the regulating groups are listed and described below.

-       Institute of Environmental Sciences and Technology (IEST)

-       Food and Drug Administration (FDA)

-       International Organization for Standardization (ISO)

Conclusion

1. A humidity chamber is a mechanism that examines how products react when exposed to humidity.

2. The different varieties of humidity chambers allow testing to be completed in a static or dynamic state depending on the required data and the type of product.

3. In most cases, humidity chambers are designed, manufactured, and produced to fit the setting that the customer requires.

4. Industries use humidity chambers to judge the effect of different weather conditions on the physical, chemical, and mechanical properties of assemblies, parts, and components.

5. Humidity chambers are made of materials that ensure their durability and optimize their performance so that they can provide accurate and reliable data regarding the many factors that can cause deterioration and failure of products.