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Article | May 4, 2010
Scale-to-PLC communications link is the key
Liquid filling gets a big boost in efficiency and accuracy from an Ethernet connection
D&R Packaging designs and builds packaging solutions ranging from dry bulk and liquid filling stations to versatile labeling equipment. When a pharmaceutical company requested a semi-automatic two-head liquid-filling machine—and wanted it within three weeks—D&R needed reliable weighing equipment that would also be capable of advanced data sharing. The solution: an Evolution Model E1070 Indicator from Avery Weigh-Tronix, which has built-in standard fieldbus interfaces for Ethernet 10/100, Profibus DP, and DeviceNet. D&R Packaging’s custom-built machine is used to fill HDPE containers at speeds to 6/min. The operator places bottles into the two stations on an alternating basis and hits a start button. That causes the filling nozzle to descend into the container. The E1070 tares out the bottle weight and then signals the system’s main PLC to begin the filling cycle.
“We needed an integrated scale that would communicate with the PLC in order to control the filling process,” says Cliff Derks, an owner at D&R. “The filling process begins with the tank dispersing liquid at its full rate. The E1070’s first setpoint is configured to activate a relay in the PLC upon reaching a measurement slightly below the container’s desired weight. The PLC then commands a reduction in product flow, down to a slow trickle. The indicator’s second setpoint is configured for the final target weight, and the E1070 signals the PLC to halt product flow once the container has been filled to its proper amount.” “Not only do you get complete industrial network communications in one instrument, you get it standard,” says Gary Barke, network application engineer at Avery Weigh-Tronix. The E1070 comes standard with a NEMA 6/4x rated enclosure that ensures dependable operation in dusty or wet environments. Dual serial ports permit transference of weight information to peripheral devices or printers. Accuracy, says Derks, is another one of the E1070’s distinguishing characteristics. “The customer requested we design a system that provides an accuracy rate of +/- 0.25 percent when used to fill a 5,000-g bottle,” he adds. “Our system can fill containers within 0.5 g of the target weight-an accuracy rate of +/- 0.1 percent.”
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