PLC automates test stands

Gary Mintchell -- Control Engineering, 12/1/1999

EG&G Engineered Products Inc. (EG&G EP, Beltsville, Md.) builds components for engine and aircraft frame manufacturers, such as McDonnell Douglas, Boeing, and General Electric. In the past, EG&G EP used manual test stands to performed threshold tests on components. Safety, accuracy, and customer satisfaction motivated engineering test and development lab personnel to seek an automated approach to performing the tests.

An incident during a typical high-pressure test prompted EG&G EP to investigate the feasibility of building containment enclosures around the test stands. Although an enclosure increases safety, it makes monitoring test parameters, collecting data, and adjusting mechanical components in the stand more difficult for the technician.

In addition to increased safety, EG&G EP wanted to improve accuracy in setting and maintaining test parameters and provide more test data for customers. By employing an automatic data acquisition system, data points could be increased and reported in an easy-to-read format with minimal technician involvement.

Similarly, Acquired Data Solutions Inc. (ADS, Alexandria, Va.) developed a data acquisition system that can be automatically operated outside a test stand enclosure. The system centers around a programmable logic controller (PLC) from Omron Electronics Inc. (Schaumburg, Ill.). ADS chose PLC control because of its reliability and ability to control such critical functions as collecting sensor data and opening and closing pressure valves.

EG&G EP selected Omron's C200H Series PLC for the test stand application because of its user-friendly programming interface, reliability, repeatability, and low cost. The PLC controls and maintains temperatures at approximately 500 7°F through a PID control loop; cycles pressures between 0 and 85 psi; monitors and collects temperature and pressure data; and communicates the information to a central Microsoft Windows NT workstation for processing and storage. ADS saved design and implementation time by using several components implementing temperature control feedback loops.

ADS wrote a ladder logic program allowing the C200H to perform other functions, as well as shut down the PLC when an operating parameter goes out of range. ADS also wrote another application to remotely monitor data collection from the PLC in real time using graphical user interfaces (GUIs) developed with National Instruments' (Austin, Tex.) LabView. GUIs permit technicians to enter inputs not gathered by the PLC. This application dials a pager that contacts an off-duty technician if test parameters are not maintained. ADS integrated ODBC into LabView to pass sensor data to Microsoft Access for analysis and report generation.

This integrated approach provided a turnkey solution that met EG&G EP's requirements. The system is secure and self-contained, allows the operator to monitor data, and presents customers with easy-to-read reports. Also, technicians can remotely run pressure tests from the laboratory, their desks, or anywhere outside a containment enclosure.

For more information circle the following or go to www.controleng.com/freeinfo.Omron Electronics www.omron.com National Instruments www.ni.com