EIT Instrument Markets * EIT Inc.

FUNDAMENTALS OF UV MEASUREMENT

What a UV Radiometer Will Do For You
Intense ultraviolet light is used in many industrial applications. While UV offers many advantages over conventional drying methods, it has its own requirements for maintaining process control. In particular, the UV lamps and irradiators deteriorate over time causing less UV energy to reach the cure surface. As the UV energy decreases, adjustments in the process must be made to maintain product quality. The difficulty is in determining when the UV energy is decreasing. Ultraviolet light is generally considered to be wavelengths in the 200nm to 400nm region, recognizing some "deep" UV exists down to 180nm. These wavelengths of light are too short to been seen by the human eye. Just looking into a curing system to see if it is still working will not tell you if the system is actually producing any UV. In fact, as some UV lamps age and the UV is dropping off, they actually produce more visible and infrared light causing them to look brighter. The only way to monitor the condition of these UV reactors is by using instrumentation with UV specific filters.
Why would you want to measure UV used in industrial processing? There are several answers. During setup, "sacrifice" workpieces are run through the process to determine if the curing conditions produce the desired results. This may require several runs and the loss of several pieces until the process has been adjusted properly. By measuring the UV energy when properly cured product is being made, all that has to be done the next time is to adjust the curing system until the same UV levels are achieved. It is not necessary to go through the same time consuming, wasteful setup routine.
UV lamps are expensive and should be replaced only after they no longer produce a usable level of UV energy. Depending on the lamp, the curing system, and how well the system is maintained, UV lamps may last less than 250 hours or well over 3000 hours. UV output must be measured in order to replace lamps only when necessary. The same goes for the reflector assemblies inside the UV irradiator. They, too, are costly and should only be replaced when required.
The cost of downtime when a curing problem has been detected often far outweighs the cost of replacement components and the cost of a radiometer. By using a radiometer to monitor UV output levels, preventive maintenance can be scheduled at a convenient, less costly time rather than right in the middle of a production run.
Using a UV radiometer can save time and money in the following areas:

Set-up time reduced
Reduce cost of "sacrifice" workpieces
Replace lamps only when necessary
Replace reflectors only when necessary
Avoid costly, inopportune downtime
Avoid production of unsatisfactory product
To be able to produce quality product consistently is really the end goal in any process. By monitoring UV levels in a curing system, it is possible to produce quality product time after time and avoid the production of bad product due to improper curing. It is very difficult to measure the cost of producing bad product. Of course, the cost of the materials and labor is lost. In addition, the cost of bad product increases exponentially the closer it gets to the customer before it is discovered. Just think of the loss of goodwill if bad product gets into the customer's hands, not to mention transportation costs, replacement costs, and administrative costs. In some very critical applications, such as medical devices, there are liability costs, as well.
Some companies may be required to have a means of quantifying their UV curing processes because they must meet a MIL or ISO-9000 specification. If these or other statistical process control requirements are to be met, numbers must be attached to elements of the process. Once this data is accumulated, the process can be fully analyzed for variability, trends, preventive maintenance programs, etc.

EIT, Inc., 108 Carpenter Drive, Sterling, VA 20164
Phone: 703-478-0700 · Fax: 703-478-0815

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