Modular control components make small-scale systems easy

By Control Engineering Staff September 6, 2006

The process illustrated uses McMillan components, including model 250 multifunction display and alarm output card, model 104-9 liquid flo-sensor, and cable assembly..

Creating a small control system in-house is easy if you choose a few simple components, as this example shows. Runoff from a food inspection operation collects in a sump that is equipped with a pump serving as a lift station. When the sump fills to its specified level, the pump empties it into a larger storage tank. To promote decomposition of contaminants in the runoff, the plant needs to add a specific amount of a chemical reagent to each sump load.

To automate this process, the customer chose a group of McMillan standard components, including a flow meter, multifunction display, alarm output card, and appropriate connecting cables. A current sensor was added to the lift station pump motor to signal the display alarm each time it empties the sump. When the lift station pump stops after cycling, the control panel energizes the reagent dispensing pump. Operating in totalizer mode, the flowmeter measures the desired amount of reagent and shuts down the dispenser once the next dose has been pumped into the sump. This process repeats every time the sump empties.

Such multi-function components can perform a wide variety of tasks and are easy to program. When combined with compatible supporting devices and wiring harnesses, they can automate small but necessary tasks quickly and economically.

–Control Engineering Daily News Desk Peter Welander , process industries editor