Like the test pilots and Mercury astronauts in Tom Wolfe's The Right Stuff, who sought to "maintain an even strain," wastewater effluent also benefits from even treatment.

Orenco Systems Inc. (OSI, Sutherlin, Ore.) manufactures wastewater treatment products that collect, convey, and filter effluent. All its packaged septic tank/pump systems include pump panels with control and alarm features that use "timed dosing" to carry out OSI's wastewater treatment philosophy. This method treats effluent evenly, in small doses over a 24-hour period, which OSI says improves wastewater treatment and prevents overloading of drainfields and sand filters. A typical OSI system uses float switches hardwired to relays, diners, and counters.

Though some large devices have been replaced by digital products, which frequently require costly, customized PC interfaces for field reprogramming or set up, OSI stuck with hard-wired devices—that is, until its engineering staff learned about logic modules. To ensure pump panel reliability and affordability, OSI recently revamped many of its panel designs to include "Logo!" digital logic modules from Siemens Energy and Automation (Alpharetta, Ga.).

OSI uses palm-sized Logo modules that can snap onto a 35-mm DIN rail and digitally replace the traditional relays, timers, counters, and alternators in its pump panels at no more than ¼ the combined cost of the six or eight former devices.

The standard 72 x 90 x 55-mm module included in OSI's pump panels has a LCD screen and built-in programming keys. It can operate on 12 V dc, 24 V dc, or 115/230 V ac, and is used in single-pump applications. OSI also uses a 126-mm wide module with more memory and features for multi-pump applications.

Though a PC can be interfaced to the device, it isn't necessary because there is minimal programming to learn. The module's functions are stored in a function block library, including on-delay and off-delay timers: up/down counters; pulse and latching relays; and 24-hour clocks. The basic module features six digital inputs and four digital or relay (8 A) outputs. Logo's wider version has 12 digital inputs, eight digital or relay (10 A) outputs, an impulse relay function, and an operating hours counter.

Logic modules increase the versatility and reliability of OSI's pump panels and reduce costs at the same time. Besides replacing many former components with one module, Logo needs minimal wiring, which can halve assembly time and save labor costs. The module's decreased space requirement allows OSI to reduce enclosure size, which further cuts production and shipping expenses.

Reduced size and cost have also allowed OSI to incorporate additional components. For example, OSI's panels, which previously offered one timer to control pump cycles, can now have two or more timers to manage flow conditions. Enabled by Logo, OSI's panel designs can use the module's clock generator function to program panels to emit steady or blinking alarm light signals. Previously, a second light and two added relays would have been needed.

The logic module's built-in delay timers increase the reliability of OSI's panels by eliminating potential contactor chattering. With previous panels, a bad float switch could cause chattering of the contacts, which can burn out the main contactor.

In addition, Logo includes a non-volatile, removable EEPROM card option. This allows field technicians to make system changes or upgrades by plugging in a pre-programmed card, rather than retrofitting and reinstalling an entire panel.

In the future, OSI is exploring new uses for the logic modules. For instance, OSI is examining an AS-interface (AS-i) for more complex applications. Adding AS-i could expand the available digital input and output capability presently in the module.

For more information, visit www.controleng.com/freeinfo .