By Rainer Storbeck

Summary: Presented with a quality control problem a couple of years ago in testing drinking water treatment units incorporating ultraviolet disinfection as they came off its production line for UV intensity, Amway turned to a specialist in detection systems to provide better assurance that units were operating effectively.


One of the more recent popular products marketed in Asia by Amway Corporation of Ada, Mich., is a carbon filtration and ultraviolet (UV) light disinfection unit for countertop residential water treatment use. As performance of the unit is dependent upon effective transmission of UV light through the water being treated, it incorporates a new testing system that provides purchasers with assurance their water treatment devices are operating according to specification, thus ensuring the highest possible levels of water quality.

Amway, with more than 450 products to its name, is one of the world’s largest direct selling companies. It has more than 14,000 employees around the world and a distributor force of more than three million worldwide, recording global sales of more than $5 billion in estimated retail for the fiscal year 1999. Amway has affiliates in 49 countries and the majority of its business is outside North America. The carbon/UV unit discussed in this article has been introduced in Taiwan, Hong Kong, Malaysia and Indonesia. A similar unit with more advanced electronic features was introduced in Japan and South Korea.

Sensing the intensity
Optical sensors that have been used to test UV water treatment systems can be fooled by ambient light, occasionally allowing a system with a defective lamp or electrical component to pass the test. The new testing system incorporates a detector from Solar Light Inc. of Philadelphia, Pa., that directly measures UV intensity. Also, optical sensors require frequent replacement, causing line-down situations periodically.  The detector is more reliable by a factor of 12-to-1. Thus, the new testing device has paid for itself many times over in reduced warranty expenses and in higher customer satisfaction.

A typical carbon block filter removes chlorine, and to a limited degree, other lightweight volatiles. The Amway unit uses UV light to kill disease-causing viruses, bacteria, algae and fungi. By providing totally chemical-free disinfection, UV does not impart any taste or odor to the disinfected water. And minerals some view as beneficial, such as calcium and magnesium, are not removed or altered. UV disinfection is also economical compared to other disinfecting technologies, such as ozonation.

The high intensity UV irradiation generated by the mercury lamp within a quartz sleeve is at 254 nanometers (nm)—or the germicidal wavelength—and is driven by an electromagnetic ballast and starter, providing the disinfection in the water treatment system. Defects in any of these components can prevent the system from operating properly. In the past, units were tested on the production line by having an operator insert a probe into the water treatment system. The probe was designed to reflect light from the lamp back to a photocell detector that recorded the light intensity. Testing was performed on every unit as soon as assembly was completed.

Ambient light
The problem with this testing method was that the optical sensor didn’t distinguish between UV and visible light. UV light falls within the 180-to-400 nm wavelength range (UVA/UVB/UVC spectrum is 180-to-400 nm), while visible light is in the 400-to-750 nm range. Any slight misorientation of the probe could cause it to pick up ambient light and pass the test even though the lamp or starter was not working. While this was not a frequent occurrence, it happened often enough that Amway management insisted on an improved testing method.

The important part of the new testing system had to be a detector that distinguishes between UV and visible light. Dave Vachon, Amway’s mechanical process specialist assigned to the task, examined several available detectors and selected the Solar Light detector. The key advantage was that it provides a high resolution 0-to-4-volt output that makes it easy to distinguish between a working lamp and background UV sources such as fluorescent lights. The other systems that he looked at had only a 0-to-1-volt output, which would provide a less reliable reading. These other systems could be converted to provide the desired 0-to-4-volt output but that would require a separate interface unit, which cost about $1,000 and would also introduce extra complexity into the testing system.

Stable response
The Solar Light detector was designed to provide an accurate measurement of UV irradiation from artificial sources. It’s applicable to wastewater treatment facilities, potable water treatment, air monitoring or air sterilization equipment for any type of airborne disease, food packaging and medical disposables—anywhere germicidal lamps are used. The unit has fast response, making it suitable for dosage measurements; and it’s small in size, rugged and affordable.

Solar Light has a strong history of innovation in the solar detector and simulator fields. Founder Daniel Berger invented the world’s first UV solar simulator in 1967, as well as improved meter technology to measure UV irradiation from the ultraviolet to infrared in narrow or broad bands up to 10,000 nm. The company can create custom configurations to meet almost any industrial safety and hazard monitoring need. Its detectors also are used to evaluate products that protect against UV light, such as suntan lotion and cosmetics. With UV increasingly present in the workplace for curing, welding and measuring photodegradation, such detectors are called upon to determine efficacy and safety, often under special conditions such as temperature extremes or water immersion.

Testing process
Vachon used the detector as the core component of a new testing system for the Amway unit. The water treatment system comes down the assembly line on a conveyor to the test station. The operator puts the unit onto a fixture and inserts the probe consisting of a long, 3/8-inch diameter aluminum tube. With the detector’s probe inserted into the system, light passes through a hole in the probe striking a dichroic mirror reflecting the UV light up the tube to the detector’s photodiode. Then the operator presses a button to begin the test. An air cylinder is activated to connect power from a General Purpose Interface Bus (GPIB), also known as an IEEE-488 Bus, for a controlled power supply to the water treatment system. This connector applies voltage to the starting system and activates the UV source.

The analog output from the detectors is fed into an analog-to-digital converter card in a personal computer. LabView data acquisition and analysis software from National Instruments is used to collect the data from the detector and, depending on whether the signal is above or below the present threshold voltage limit, makes a pass/fail decision. The detector measures the presence of germicidal irradiation only, making it impossible for ambient light to provide a false reading. The new testing system also performs several electrical tests including current draw and the functionality of the appliance leakage circuit interrupt that protects the user against shock in the case of a short circuit.

Application assistance
Vachon said Solar Light was extremely helpful in developing the new testing system. “They helped me to interface a PC with an analog-to-digital converter to the detector and gave me advice on setting threshold limits. They also helped by calibrating our detector to NIST-traceable standards.”

Conclusion
The new testing system provides Amway customers with the highest possible levels of quality. Since it was installed, not one single case of a water treatment system with a faulty ultraviolet source has been found to pass final inspection. The ability of the UV detector to distinguish between ambient light, background ultraviolet sources and working disinfection units made the difference.

About the author
Rainer Storbeck is with Structured Information, a Birmingham, Mich., public relations firm. He can be reached at (248) 540-5610, (248) 540-3506 (fax) or email: rainer@strucinfo.com

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