PC-based multichannel data-acquisition equipment

Situation

An aging data acquisition system at Sawyer Research Products Inc. (Eastlake, Ohio), producer of high-quality quartz crystal for electrical component manufacturers, was limiting efforts to improve process reliability and overall yield. Growing quartz crystals requires high precision and constant monitoring and adjustment of process temperatures. The company felt its operation was in jeopardy from a reliability standpoint, because it monitors temperature data from the autoclaves to track the culturing process from start to finish. It's critical to accurately monitor the autoclave temperatures, since crystal growth is controlled entirely by maintaining internal autoclave temperatures at optimum levels throughout the process. The old manual controllers were unwieldy and unreliable, requiring a technician or engineer to physically walk to each individual autoclave each time a temperature adjustment is necessary. The crystal growing process is controlled with skin temperature, so replacing the old controllers to bring skin temperatures into the data acquisition system also was important.

Objectives

• Streamline the entire process
  
• Find an affordable solution
  
• Automate temperature control
  
• Install equipment that meets current standards
  
• Easy equipment upgrade without custom programming
  
• Expandable and flexible equipment

Solution

The company implemented a three-phase project to fully automate the entire crystal-growing process at the Eastlake plant by replacing their antiquated data acquisition system. The equipment had to meet current standards, future software upgrades and modifications had to be possible without custom programming and the new system had to be expandable and flexible well into the 21st century. After looking at several approaches to find a solution that was affordable and equally capable of handling the technical rigors of the application, Sawyer turned to Yokogawa Corporation of America (Newnan, Ga.), a leading manufacturer and supplier of process, test, and measurement instrumentation.

Yokogawa's Darwin series DA-100 is the functional heart of Sawyer's new system. While the stand-alone unit is capable of monitoring up to 40 channels, the expandable unit can track up to 300 channels, and provides enough flexibility to handle applications ranging from small-scale data logging to large multipoint data acquisition applications. Sawyer's Eastlake facility consists of 405 autoclaves, distributed evenly among nine buildings. Taking advantage of the DA-100's modular configuration, the facility was divided into three building groups, using a single DA-100 linked to a PC as the data acquisition hub for each group. A fourth PC and remote monitor were installed in the facility supervisor's office to track the entire system.

Polling two data channels per autoclave, each DA-100 hub acquires 270 channels of data from a pair of Darwin DS-400 and DS-600 modules in each building. The DS subunits, capable of feeding up to 40 and 60 channels, respectively, back to the DA-100, are wired to the autoclaves via thermocouples. Replacing all the old wiring with J-type thermocouple extension wire was also a necessity to eliminate ongoing resistance problems with the old copper wire used to transmit growth chamber temperature.

"We used to use a differential hook up to manually calculate the change between the growing and dissolving chambers," said Sawyer's Process Control Engineer Glenn Kleckner. "With the new system, we can run both sets of temperature data straight through Darwin and calculate the delta in the computer," he added.

The new controls allow adjustment of temperature set points from the computer, and provide improved programmable warm-up control. Manual temperature charting is replaced with real-time trending, and the creation of a historical database is used as a base for analysis and to create physical models and new control algorithms.

"Engineering and manufacturing are married on a minute-by-minute basis in our business," said Kleckner, "and data acquisition technology is finally enabling us to take better control of our overall process through real-time data analysis and to gain new insight into the hard science behind what we do."