Circular geometry measurements of rotors for gas turbine generators are important. The rotating parts of a turbine rotor unit range up to 96 inches in diameter, 120 inches in length and weigh up to 25,000 pounds. During assembly, approximately 24 of these components are stacked and bolted together to form the spinning core of the power generation unit. The accuracy of these components is critical to the performance of the finished unit. If each part is only a few thousandths of an inch off, the accumulated tolerances will result in a "stack," in which the bearing surfaces are out of alignment. This can lead to premature bearing wear and possibly failure.

Using current manufacturing methods, it is virtually impossible to build these massive parts with small enough tolerances so they can be bolted together without inspection. Instead, turbine manufacturers attempt to accurately measure each of the rotors in the assembly. They then match the rotors based on their flatness measurements so that the entire stack will run true. However, the parts’ sizes mean that an enormous number of data points must be collected to have an accurate match. And high production volumes leave little time to perform the necessary measurements. An environment with high vibration and noise adds an additional challenge.

Turbine Metrology’s (Kansas City, MO) Paragon system acquires over 1.2 million samples per second, making it possible to perform all the necessary measurements in a single revolution of the rotor. The company designed its Paragon system so that rotor manufacturers could collect more samples in a single revolution. "The mechanical aspects of the process are difficult. These large and heavy rotors must be centered and rotated accurately enough to prevent their run-out from affecting the measurements," says Neill Fleeman, technical director. "We also needed to eliminate the influence of external seismic and acoustic inputs. Because restacking an assembled rotor can cost upwards of $150,000, these measurements are critical."

The Paragon system has mechanical underpinnings and uses precision air bearing rotary inspection tables from Eimeldingen Ltd. (Bath, England). Heidenhain (Schaumburg, IL) encoders read the angular position of the table. Paragon can handle up to eight input channels. In the standard system, four electronic lever-type gauge heads from Brown and Sharpe (North Kingston, RI) trace the surface of the part to 0.000004 inch. These components generate a vast amount of information from a turbine rotor in a short period of time.

Once the company developed a system that would allow rotor manufacturers to accurately take measurements, the biggest problem was developing a system to process the enormous volume of data required to thoroughly characterize parts of these sizes.

Using a single server to handle both processes created a problem. A fast and accurate data acquisition system that could run independently of computer’s operating system was needed. This would allow the operating system to process the data that had already been collected.

The solution was Microstar Laboratories’ (Bellevue, WA) iDSC 1816 data acquisition processor (DAP) board. The DAP board simultaneously collects and processes data apart from the host server. This makes it possible to quickly and thoroughly evaluate the huge rotors as soon as they are machined. The rotors can then be stacked with others whose dimensions complement their own to produce smooth-running turbines. It can sample analog inputs at a rate of 1.2 million samples per second.

The iDSC 1816 also has an onboard microprocessor that runs a multitasking, real-time operating system optimized for high-performance data acquisition and control applications.

There is never any danger of losing data. The data acquisition processor continues to run the special routine that collects data from the acquisition devices totally independent of the central processor.

With the DAP board in place, the Paragon system can characterize the turbine rotors by collecting 720,000 measurements in a single revolution. This enables rotor manufacturers to accurately determine their dimensions early in the manufacturing process.

For more information on data acquisition processors, call 425-453-2345 or visit