Master Sgt. Lars Mirandamuller, AEDC PMEL/Chemical Laboratories section chief, and Dave Compton, Aerospace Testing Alliance (ATA) PMEL manager, examine a high voltage divider during a recent inspection held annually at one of the most unique calibration labs in the world. (Photo by Jacqueline Cowan)
11/30/2012 - ARNOLD AIR FORCE BASE, Tenn. -- When Arnold Engineering Development Complex's (AEDC) engineers conduct mission-critical flight simulation testing on leading-edge aerospace systems, including aircraft, rocket motors, spacecraft and missiles, they rely heavily on what the Complex's Precision Measurement Equipment Laboratory (PMEL) provides.
What PMEL's workforce does is the "behind the scenes" effort that ensures that the test data is consistently accurate.
"Data is the reason we test," said Lt. Col. James Peavy, AEDC's Turbine Engine Ground Test Complex (TSTB) Test Division Branch chief. "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. PMEL has the folks that 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 at AEDC there are hundreds of hours of hard work and support from the PMEL shop."
Dr. Ed Kraft, AEDC Chief Technologist, said the AEDC's PMEL is not only unique, but has an excellent reputation for a good reason.
"The PMEL is responsible for assuring all the critical instruments we use in the test facilities are calibrated to be consistent with the NIST (National Institute of Standards and Technology) and that's the whole foundation of assuring we have quality data in our test facilities," said Kraft. "One [factor] is the nature of the work we do here and then the magnitude of it, too. They [PMEL's 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."
Dr. Kraft credits the lab's far-reaching and solid reputation among the complex's customers to the highly-skilled technicians, the forward-looking management of PMEL's leadership and the lab's state-of-the-art equipment.
PMEL has long provided AEDC's 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 that are traceable to the NIST. These are standards recognized nationwide.
Certified by the Air Force Metrology and Calibration (AFMETCAL) program facility in Heath, Ohio, PMEL has even led the way in setting measurement standards for the military.
Dale West, ATA's supervisor of the mechanical labs at the PMEL, said, "The measurements we make at AEDC 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 AEDC," West said. "Our PMEL provides that traceability back to a national standard which is the National Institute of Standards and Technology (NIST)."
PMEL includes 18 different measurement work areas throughout the lab, including pressure flow, force, mass and torque, and also AC and DC voltage electrical current, resistance, RF/microwave frequency, temperature and a dimensional measurements area.
West said the equipment throughout PMEL is "state-of-the-art and is operated and maintained in a stable, controlled environment."
Vince Chapman, with AEDC's Test Systems Sustainment Integration and Support Branch, said people like West and James Winchester deserve much of the credit for PMEL's excellent long-standing reputation among the metrology community and the customers they serve.
"Our PMEL's flow capabilities have really been a benchmark for the Air Force," he said.
James Winchester's work to improve our flow capabilities has not only benefitted AEDC, but the entire Air Force. The metrologists at the Air Force Primary Standard's Laboratory have learned a tremendous amount from Mr. Winchester's work. They, in turn, have implemented many improvements with Air Force liquid flow calibration methodologies which have directly benefitted other bases in the Air Force Material Command, including Hill AFB, Utah and Tinker AFB, Oklahoma."
Winchester, who spent much of his 32-plus year career as an AEDC PMEL metrology and instrumentation & 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 AEDC, but for AFMETCAL, the Air Force, Army, and DOD facilities worldwide, according to Chapman.
PMEL Technical Manager Greg Holcomb said PMEL is comprised of a number of 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 PMEL 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. "The PMEL 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 PMEL 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 RF (radio frequency) and DC (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 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 at AEDC's PMEL, 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 for PMEL - 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 noted. "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 METCAL to ensure that everyone's in agreement with how to calibrate and certify equipment."
Currently a senior engineer with ATA's technology branch, Winchester sees a bright future ahead for AEDC's PMEL, despite ongoing economic challenges.
Winchester and Holcomb credit their team's academic backgrounds, on-the-job mentoring and the equipment available at AEDC in providing them all with the specialized skills to excel in their field at Arnold's PMEL.
"We have the calibration standards to meet the requirements of the state-of-the-art instrumentation that is used in the test cells at AEDC," Holcomb said. "The engineering and management support for the PMEL 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 at AEDC 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.
"The AEDC PMEL is well positioned to meet the upcoming calibration challenges of today's Air Force and future requirements," Holcomb said. "We have the best trained technicians that can adapt to the rapidly changing technology requirements of metrology."