PLCs Automate Reliability Testing

By Barry Hupp, Reliability Manager, Viking Range, Greenwood, Miss.

When Fred Carl, Jr. was designing his house in the early 1980s, he wasn’t satisfied with the quality of available ranges. He came up with his own range design, and soon thereafter launched Viking Range. Established on Carl’s requirements for high reliability and quality, further improvements were sought through automated testing.

An in-house dishwasher lab and the cooking/refrigeration lab are two main reliability test areas. Viking started the dishwasher lab in 2003, and the cooking and refrigeration reliability lab in late 2005. Before creating them, the product engineering department conducted its own testing. At that time, product engineers were not using PLCs, and testing products manually was difficult, which presented a need to build several automated test stands for testing components to be used in dishwasher designs.

Automated testing of products like this range enables Viking Range to provide high quality products with superior reliability to their demanding customer base.

By automating the test labs, Viking aimed to reach several goals. Cutting test time and reducing labor requirements were necessary to standardize test procedures with industry standards, and improve product testing in general. Automatic recording of test data would allow analysis and improvement of test procedures. Finally, better test data would enable product designs improvements.

Designing these new products started Viking Range on an evolutionary path toward creating reliability test labs and using PLCs to automate test-stand operation. DirectLOGIC DL06 PLCs from AutomationDirect were used to reach these goals. The PLCs were inexpensive, and could measure everything needed to test the dishwasher components to build more test stands—as well as start the cooking/refrigeration lab. Using both ac and dc input versions of both PLC models thermocouple and 0-10 Vdc analog input were included while using relay outputs instead of analog or discrete outputs.

In 2003, six test stands were created, designed, and built to ensure that dishwasher components exceeded standards for long-term reliability. The components tested were dishwasher motors, drain pumps, water valves, soap dispensers, water heaters, and heaters/blowers for drying the dishes. Building a separate test stand or fixture for each of these part/component types, each of the fixtures had the capacity to test 22 components. A DL06 PLC controlled each fixture except for the water valve fixture, which used a DL05 PLC.

Over the years, changes to the test fixtures and PLC configurations accommodated reliability testing requirements. Today, part of the original dishwasher test lab uses three DL05 PLCs, instead of the initial DL06 PLCs. These PLCs are mounted on custom stands that test individual dishwasher parts such as, soap dispensers and pump and drain motors.

This custom door cycle fixture performs life testing by opening and closing a wall oven door up to 50,000 times, depending on test requirements.

Other dishwasher life testing tasks included a door cycle fixture for opening and closing a dishwasher door from 30,000 to 50,000 times; an upper slide rack fixture that tests a dishwasher’s upper rack by sliding it in and out; and a fixture that tests dishwasher water valves by cycling them on and off repeatedly.

The main reliability lab—also known as the cooking and refrigeration test lab—is the largest testing facility. Testing ranges, wall ovens, cook tops, refrigerators, icemakers, and compactors, the lab uses more PLCs than the other labs, with most of them monitoring range temperatures. The DL06 PLCs operate test stands and control cycle times for ranges between 30 min on and 10 min off for 6000 cycles.

Range and wall oven doors receive rigorous workouts as well. In the cooking and refrigeration test lab, two test stands each with a DL05 and C-more HMI operate and monitor the range and wall oven door open-and-close cycles. The HMIs display the cycle counts, while the touch screen keyboard allows test engineers to reset the count.

DL06 PLCs measure temperatures of ranges, ovens, and cook tops under test. Thermocouples are attached to analog inputs cards and the PLCs are programmed to run repetitive cycles that turn units on for an hour then off for 15 minutes.

DirectSOFT5 Windows-based PLC programming software allowed writing or modifying test programs to the appliances or component parts, without much in the way of prior experience.

The PLCs have enabled continuous component and product testing for more than seven years without any problems. Due to Viking Range’s success with AutomationDirect products, it now uses DL05 and DL06 PLCs in two other manufacturing plants for monitoring and testing products.

Viking Range
www.vikingrange.com

AutomationDirect
www.automationdirect.com

::Design World::