Texas weather had the maintenance crew scrambling with brooms and shovels at Cargill Foods' Dry Milling Division plant in Saginaw. Load cells used to measure the contents of finished flour bins were failing due to variation in temperature and air moisture levels. In the fall and spring, bins sometimes overflowed on a daily basis. Daily temperature swings during the summer only perpetuated these problems.

"It was a real mess, losing product and production time in our packaging center," says Roger Grinstead, maintenance technician at the plant. "Some spills were so large we were forced to shut down bagging machines several hours for clean up and repair."

Grinstead found a simple solution in Milltronics' ultrasonics system with a SmartLinx interface card, using standard Allen-Bradley Remote I/O protocols and direct links. SmartLinx fits a number of Milltronics controllers, including the AiRanger XPL Plus controllers that Grinstead chose for Cargill's bagging plant. They allowed Cargill's existing Allen-Bradley PLC-5/25 to access all instrument data from the AiRangers using standard block transfer protocols.

"It was much easier to install ultrasonics than it would have been to replace the load cells," adds Grinstead. "Setting up all 12 bins took two of us just two days, including programming. By comparison, it took two weeks for a four-man crew to install the load cells."

Milltronics' systems uses high frequency sound wave and advanced echo-processing software to monitor the level and movement of materials, despite airborne contaminants such as dust. The Cargill plant operates a 24/7-work schedule, producing up to 1,200 tons of flour per day.

"This is a dynamic operation, with most bins filling and drawing at the same time," notes Grinstead. "Flour is blown into the bins pneumatically at 30,000 lb. per hour." The 18,000-lb. capacity, 6-ft. diameter, 20-ft. deep bins begin filling when levels drop below 7,000 lb. and shut off when levels reach 17,000 lb. The ultrasonics system is fast enough to follow each level, detect the high cutoff point then transfer the data to the Allen-Bradley PLCs in time to stop the conveyors and prevent overfill.

Cargill chose AiRanger XPL Plus controllers because of their speed and capacity of controlling up to 10 ultrasonic points each simultaneously.

Milltronics, 709 Stadium Dr., Arlington, TX 76011. Tel.: (817) 277-3543; Fax: (817) 277-3894