The Industrial Physics FAQ guide to permeation testing
Why is water vapor permeation testing important? And how do permeation testing instruments help you?
Let’s start with the first question…in fact, there are several reasons, depending on what you make and how you make it.
We can take a look at an obvious one – food packaging. Nobody wants a soggy, stale potato chip, right? But there’s also more to this to consider. Inadequate impact doesn’t just impact on shelf life – it can also lead to changes in flavor, color, or nutritional value.
Discovering the best water vapor permeation instruments
In response to this Industrial Physics has developed some of the best water vapor permeation instruments on the market. You could say we have permeated the market with our innovative machines.
In fact, you can take a look at our suite of water vapor permeation instruments and oxygen permeation testing instruments in our permeation testing guidebook here.
Techniques for water vapor permeation measurement
Traditionally a WVTR testing, and permeation rate calculation measurement system consists of a wet and adjacent dry chamber, separated by a sheet of barrier material.
Observing ‘Fick’s Law’, strict control of the wet and dry environments can be used to calculate the water vapor transmission rate through a barrier. The law states that diffusion through a barrier is a linear function of the concentration gradient across the barrier and its thickness.
There’s several sensing methods for water vapor permeation measurement. The most common techniques are to use infra-red (IR) light spectral absorption methods.
NDIR is well established and is popular for permeation testing. It’s typically based on the absorption of a single optically filtered peak. And many suppliers rely on it as a well-established, reliable permeation method.
Let’s talk about the coulometric sensor option – the latest technology, the P205, with a new ASTMF3299-18 standard. It’s based on the electrolysis current of the water vapor absorbed in a hygroscopic material; the technology of choice for several permeation instrument manufacturers. Industrial Physics has developed these sensors for many years; our permeation testing instruments provide an economical, yet highly accurate solution.
Water vapor measurement instruments calibration and standards
Most IR sensor-based permeation testing instruments have a characteristic response to water vapour concentration. This is down to the design of the instrument detector, which can be subject to drift over time. Consequently, such devices need regular calibration.
In contrast, the P205 coulometric sensors follow ‘Faraday’s Law’, which relates to the electrochemical dissociation of a water molecule to precisely two electrons; thereby providing a current which is absolutely related to water consumption levels.
Calibration standards are available in the form of traceable gas bottles, producing standards over the range 5-2000 ppbv.
Comparison of commercial water vapor measurement instruments
There are two classes of commercial permeation testing instruments for measuring water vapor transmission rate commonly available. These are the NDIR spectroscopic absorption designs and the coulometric instruments.
NDIR spectroscopic permeation testing instruments are not absolute, so periodic calibration against a standard will be necessary to combat any drift and to maintain accuracy.
Coulometric water vapor transmission rate measurement typically requires a little more housekeeping in the form of sensor maintenance, but beyond that, modern digital instruments are straightforward and user-friendly. Benefits include absolute measurements, directly related to the precise amount of water vapor transmitted, which don’t require the use of a standard. The latest instruments have already exceeded the sensitivity of the NDIR types, with further improvements within reach.
Industrial Physics’ instruments specialize in coulometric P205 type permeation rate calculation. If you need to understand the best type of permeation test for your organization, then get in touch today. We have been at the forefront of research and development of water vapor permeation and gas permeation testing instruments for many decades. We love what we do and we’re only too happy to help.