TULLAHOMA – When the Engineering Development Complex’s engineers at the Arnold Air Force Base conduct mission-critical flight simulation testing on leading-edge aerospace systems, including aircraft, rocket motors, spacecraft and missiles, they rely heavily on what the Precision Measurement Equipment Laboratory provides.
Master Sgt. Lars Mirandamuller, a Chemical Laboratories section chief, and Dave Compton, Aerospace Testing Alliance manager, examine a high voltage divider in Nov. 30, 2012, at Arnold Air Force Base in Tullahoma, Tenn. (Photo courtesy of U.S. Air Force)
What the lab does is the behind-the-scenes effort that ensures test data is consistently accurate.
“Data is the reason we test,” said U.S. Air Force Lt. Col. James Peavy, chief of the Turbine Engine Ground Complex Test Division. “If we don’t accurately measure and record the event then, in effect, it never happened. It is critical to have instruments with the accuracy and precision to measure both the expected and unexpected events. (The lab) has the folks who do this vital work for us. You can’t have a world class test facility without a world class instrumentation capability. They rarely get the credit they deserve, but for every successful test we do, there are hundreds of hours of hard work and support from the shop.”
Ed Kraft, chief technologist for the complex, said the lab is not only unique, but has an excellent reputation for a good reason.
“It is responsible for assuring all the critical instruments we use in the test facilities are calibrated to be consistent with the National Institute of Standards and Technology, and that’s the whole foundation of assuring we have quality data in our test facilities,” Kraft said. “One (factor) is the nature of the work we do here and then the magnitude of it too.
“Technicians calibrate from 8,000 to 9,000 instruments a year, and we deal with precision measurements. If you go to a flight test, they obviously do a lot of measurements also, not nearly as precise because they can’t control the environment the way we do. The volume and the precision our folks have to deal with is what set us apart from those other labs.”
Kraft credited the lab’s far-reaching and solid reputation among its customers to the highly skilled technicians, the forward-looking management, and the lab’s state-of-the-art equipment.
The lab has long provided customers with
calibration of test measurement instrumentation such as voltage, temperature and pressure measurements and dew point standards, at the appropriate intervals to ensure measurements are traceable. These are standards recognized nationwide.
Certified by the Air Force Metrology and Calibration Program facility in Heath, Ohio, the lab has even led the way in setting measurement standards for the military.
Dale West, a supervisor of the mechanical labs, said, “The measurements we make at (the complex) in our test cells, wind tunnels, turbine cells and our space chambers, we want those to be the same measurements that would be made anywhere else in the country.
“We’re providing traceable measurements that are made at (the complex). Our (equipment) provides that traceability back to a national standard.”
The equipment at the lab includes 18 different measurement work areas, including pressure flow, force, mass and torque, and also electrical current, resistance, microwave frequency, temperature and a dimensional measurements area.
West said the equipment throughout the lab is “state-of-the-art and is operated and maintained in a stable, controlled environment.”
Vince Chapman, who is with the Test Systems Sustainment Integration and Support Branch, said people like West and James Winchester deserve much of the credit for the lab’s excellent long-standing reputation among the metrology community and the customers they serve.
“Our flow capabilities have really been a benchmark for the Air Force,” he said.
He said James Winchester’s work to improve flow capabilities has not only benefitted the complex, but the entire Air Force.
The metrologists at the Air Force Primary Standard’s Laboratory have learned a tremendous amount from Winchester’s work, he said.
They, in turn, have implemented many improvements with Air Force liquid flow calibration methodologies, which have directly benefitted other Air Force bases.
Winchester, who spent much of his 32-plus year career as a metrology, instrumentation and controls engineer, continues to contribute to an ongoing effort to perfect flow meter calibrations for test customers at the complex.
Winchester also helped to develop more accurate flow meter calibration processes, not just for the Air Force complex, but also for Army and U.S. Department of Defense facilities worldwide, Chapman said.
Technical Manager Greg Holcomb said the lab comprises several smaller labs in an environmentally controlled building. His current role is development of increased automation of calibration processes conducted in these various labs.
“My colleagues at the (lab) also calibrate optical transits to set up test equipment in the test cells, (to) get everything on the test cell center line and properly leveled,” he said. “It also has a mass lab where calibrated weights are used for calibration of weighing scales. The mass lab also calibrates other weights which are then used for field calibrations of weighing scales.
“We also have a gas laboratory where hand held analyzers are calibrated against standard gas mixtures to make sure that workers in the field know that adequate oxygen is available in breathing air and that explosive levels of hydrocarbons are not in the air.”
Holcomb pointed out that the lab has an accelerometer and vibration sensor calibration station.
“Vibration sensors and accelerometers are used on numerous test articles as well as heavy plant equipment to detect oscillations, or if a bearing is beginning to fail or something of that nature,” he said. “Then we have the electronics lab where both radio frequency and direct current electronic equipment is calibrated.”
Holcomb continued, “We have a temperature lab and we have a hygrometry lab. In the hygrometry lab, we calibrate sensors utilized to measure moisture levels in air. This is done primarily to tell how much moisture is being carried by the air in the wind tunnels to maintain the right conditions for testing.
“The temperature lab is somewhat unique to the Air Force. We have the highest temperature standard available in the Air Force and we also have the lowest temperature standard in the Air Force. We can go from about 14 Kelvin (degrees) to 2,750 Celsius and everything in between. The low cryogenic temperatures are for sensors that are used in the rocket test area, and for cryogenic test articles being delivered for work in our space chambers.”
The higher temperatures are utilized for calibrating optical pyrometers primarily for the arc heater facility, a materials test facility for missile and space re-entry vehicles’ heat shields.
Chapman said the workforce, just like at any metrology laboratory, face challenges as technology continually evolves and calibration requirements for those technologies are worked out and established.
“The biggest challenge – looking at the research and development course of events – we’re seeing a lot of new items come in the door that they’re not accustomed to supporting,” Chapman said. “Now, they frequently have to write a test procedure or do some research to find out what’s the proper way of calibrating [the test and test support equipment].
“Plus, all of the calibrations are blessed by Air Force METCAL. So there’s a process that they have to go through – not only on this end, but also exchanging information with Air Force (agencies) to ensure that everyone’s in agreement with how to calibrate and certify equipment.”
Currently, a senior engineer with the technology branch, Winchester said he sees a bright future ahead, despite ongoing economic challenges.
Winchester and Holcomb credit their team’s academic backgrounds, on-the-job mentoring, and the equipment available at the complex in providing them all with the specialized skills to excel in their field at the base.
“We have the calibration standards to meet the requirements of the state-of-the-art instrumentation that is used in the test cells,” Holcomb said. “The engineering and management support is always looking to the future to improve the uncertainty of our calibrations and increase the automation of our calibrations to be able to support the instrumentation requirements within current budget restraints.”
Holcomb said he is confident about what lies ahead because of the teamwork between the lab’s staff and those who manage and support it.
“We are well positioned to meet the upcoming calibration challenges of today’s Air Force and future requirements,” Holcomb said. “We have the best trained technicians who can adapt to the rapidly changing technology requirements of metrology.”