Quality Magazine

Multiplexer Adds SPC Flexibility

May 5, 2003
Efficient process control often depends on the ability to rapidly access data from a large number of sources in the production environment, and with optimum accuracy. That is what Spectrum Brands (St. Louis) sought when it switched to a multiplexer link for verifying tight tolerance weights in both liquid and aerosol filling of product containers at its lawn and garden products division.

Spectrum Brands seized the opportunity when the unit's longtime statistical process control (SPC) software vendor, Hertzler Systems (Goshen, IN), upgraded to Windows-based technology several years ago. To provide the process floor interface to personal computers running Hertzler's Gainseeker SPC software, Spectrum chose the MPX-4S multiplexer from MicroRidge Systems (Sunriver, OR).

The MPX-4S unit can combine, or multiplex, the signals from up to 16 digital gages and serial devices for communication through a single RS232 serial port on a PC. In the Spectrum application, the multiplexer unit replaced "a backplane full of gage ports," says Larry Nestor, Spectrum's quality control manager. "It allowed me more flexibility in setting up programming for speaking to our Mettler balances and scales," Nestor notes.

Spectrum uses the multiplexed set up for process control in the final packaging of Spectrum lawn and garden products, including insecticides, insect repellents and liquid plant-fertilizers. The system monitors weights of liquid filler and, for aerosol products, also crimp measurement of the valve crimped into an aerosol can. Some of the filling specifications need to be so accurate that standard tare weights are not applicable.

The system configuration links four digital micrometers as well as five scales, equipped with serial outputs, to the computer. In this, explains Nestor, "there's a lot of flexibility to customize the way you program, or write the [software's] data-entry templates to communicate with the MicroRidge unit, and then on to the device or gage you're using."

The MPX-4S can handle up to four user-installable input modules, each of which can accommodate up to four devices. Nestor describes his use of the multiplexer: One module in the MPX-4S connects to the four micrometers, which provide data from filler heads on top of aerosol gages. The next two modules handle the Mettler scales; data from four scales goes through one module and data from the fifth scale through the other module. The fourth module slot of the MPX-4S is presently unused, leaving room for additional future capacity.

All this provides plenty of capacity with flexibility in the plant's process control environment, regardless of which filling line is used. "We track individual process streams through all of this data gathering," Nestor says. He notes that the rotary line of 12-head fillers presently charts as many as 84 processes. An "in-line" container-filling line, connected to the five Mettler scales, charts up to 16 separate processes currently. This is double-indexing filling with nozzles to containers on two sides of the moving line.

The system reads weights of selected containers before and after the filling processes for each container. Readings and charting can be done individually and selectively by filling head number. An operator triggers the readings, through either handheld or stand-mounted devices, with an "enter" key or foot switch.

"Part of this extensive SPC data is because of the flexibility of the software," Nestor says. "But getting the gages to the way we want to read them is because of the MicroRidge interface; that's what helps us there."

Hertzler Systems
(219) 533-0571
MicroRidge Systems
(541) 593-3500