Measurement Standards and Calibration Laboratory
WSTF supports an extensive number of test programs, most of which are instrumented for temperature, pressure, load, acceleration, and other measurements. The WSTF Measurement Standards and Calibration Laboratory ensures that the instruments used to make these measurements are accurate by calibrating them against recognized standards. A two-level tier of standards is used. The first level contains high-accuracy reference standards. These standards are traceable to the National Institute of Standards and Technology (NIST), and their accuracy is known in terms of national standards. Reference standards are highly stable and repeatable; for example, measurement uncertainty of the voltage standard is less than 0.5 ppm. The second level of standards is a group of 80+ working standards. These standards are calibrated by the reference standards and used to calibrate customer instruments in 25 major measurement disciplines.
The Measurement Standards and Calibration Laboratory has experience in providing support to NASA, other government agencies, and private industry. Current customers include NASA, U.S. Air Force, and U.S. Army. The Measurement Standards and Calibration Laboratory is certified to meet the ISO 9001 Standard.
Mechanical calibration is primarily based on mass and length, both of which exist in the form of artifacts. The other mechanical measurements are derived from these basic units. Temperature is defined by the ITS-90 (International Temperature Scale of 1990) in terms of the melting and freezing points of pure materials as measured by a standardized platinum resistance thermometer.
Physical Standards: WSTF can calibrate mass within the range of 0.5 micrograms to 30 kilograms, and length in a range from 50 microinches to 120 inches (1.3 µm to 3 m).
Pressure Calibration Laboratory: WSTF has two deadweight pressure systems: 1000 psi (7 MPa) and 10,000 psig (70 MPa). They operate using the basic definition of pressure-force per unit area. In this case, weights are placed on a piston giving pounds per square inch (psi). Using very small area pistons, it is possible to generate 10,000 psi (70 MPa) without placing 10,000 lb (4 Mg) of weight on the piston. The 1000 psi system can be operated in absolute (vacuum reference) or gauge (atmosphere reference) mode.
Straight Pressure Calibration Stations: WSTF has five stations with four different pressure ranges: 0 to 30 in. of water (7 kPa), 0 to 1000 psia (7 MPa) (one manually operated and one fully automated), 0 to 10,000 psia (70 MPa), and 0 to 30,000 psig (21 MPa).
Differential Pressure Station: WSTF has the capability of holding a base pressure of up to 250 psig (1.7 MPa) while measuring differentials in the range of 0 to 100 psi (700 kPa), or we can do differentials vs. atmospheric pressure up to 1,000 psig (7 MPa).
Flow Calibration Laboratory
Liquid (Incompressible): The liquid used is water, and WSTF can measure flows from 0.4 to 400 gal/min (1.5 to 1,500 L/min).
Gas (Compressible): WSTF has the capability of flowing nitrogen, helium, compressed air, or anything nontoxic/nonflammable that can be supplied in a standard DOT pressure bottle in the lower flow ranges: 0.0008 to 12 SCFM (0.37 to 5,400 cm3/s). In the higher flow ranges up to 200 SCFM (90,000 cm3/s) only nitrogen is available, but WSTF can test with any nontoxic/nonflammable gas the customer can supply in sufficient quantity/pressure. One customer supplied a helium tube bank semitrailer for high flow calibrations.
Temperature and Humidity Laboratory
Temperature: WSTF's temperature lab uses Standard Platinum Resistance Thermometers (SPRT) calibrated to ITS-90 as the primary standard, and can calibrate in the range from -197 ºC (liquid nitrogen) to 500 ºC.
Humidity: WSTF's humidity standard and chamber can calibrate in the range of 1 to 98 percent relative humidity, within a temperature range of 15 to 30 ºC (normally 20 to 23 ºC).
Force and Tool Calibration: We can calibrate force measuring devices in tension or compression up to 50,000 lbf (220 kN). We can also calibrate cable tensiometers vs. weights.
Torque Wrenches: WSTF can calibrate torque wrenches in the range of 3 in-oz to 1,000 ft-lb (0.02 to 1,400 N-m).
Crimpers and Strippers: WSTF can gauge, inspect, and conduct pull tests for a wide range of these tools.
Vacuum Calibration Laboratory: WSTF has a vacuum calibration system, with a range from 1000 torr (100 kPa) (760 torr is atmospheric pressure) down to 10-7 torr (10 µPa).
Software Engineering: Computer-aided calibration systems are used extensively at WSTF. Both off-the-shelf and custom designed, written by in-house staff programmers, are utilized. Electronic data can be provided upon customer request.
The Electrical Calibration Laboratory provides calibration and repair services for a wide variety of equipment types including:
- Resistance and capacitance decade boxes
- Digital and analog multimeters
- Power supplies
- Electronic loads
- Thermocouple simulators and readouts
- Current shunts
- Digitizing and analog oscilloscopes
- Microwave signal generators
- Spectrum analyzers
- Power sensors
Equipment outside of WSTF capabilities are outsourced to the manufacturer or other government laboratories, allowing customers to use WSTF's laboratory as a single source for all of their calibration support requirements. Expense statements are provided quarterly to all non-WSTF customers.
Electrical Laboratory: This station is used to calibrate microwave signal generators, spectrum analyzers, attenuators, frequency counters, amplifiers and other associated equipment. The system consists of measuring receiver, mixer, local oscillator, microwave signal generator, and spectrum analyzer. The system uses automated calibration software for most of the microwave signal generators calibrated by WSTF. Software is also used for most attenuator and spectrum analyzer calibrations.
Scope Station: All of the oscilloscopes calibrated by WSTF are done at this station. The standard is a calibration generator for timing and amplitude accuracy, and a signal generator for bandwidth measurements. This system is controlled by MET/CAL® software procedures. Seventy percent of the oscilloscopes are calibrated using MET/CAL® procedures.
Digital MultiMeter (DMM) Station: There are two calibration standards at the DMM station: a multifunction calibrator and a multiproduct calibrator. A custom subroutine was written by WSTF to allow MET/CAL® to control the multifunction calibrator, which is used to calibrate all of the benchtop multimeters of 5-1/2 digit or greater resolution. Seventy-five percent of these meters can be calibrated in a fully automated fashion using MET/CAL® procedures written by WSTF. The multi-product calibrator is used for the rest of our DMM workload, along with some thermocouple readouts and simulators. Ninety percent of the handheld DMMs are calibrated using MET/CAL® procedures.
Reference Standards: WSTF Measurement Standards and Calibration Laboratory reference standards are maintained in the shield room. The volt is represented by a bank of three voltage cells. They are calibrated by the NASA Portable Josephson Array Voltage Standard (PJAVS). The PJAVS returns to WSTF approximately every 6 to 9 months. The ohm is represented by an Thomas-type1-ohm standard resistor. This resistor was originally acquired in 1964, and since then has been the WSTF ohm standard. The value of this resistor is maintained by annual calibrations by higher laboratories, primarily NIST and the Primary Standards Laboratory at Sandia National Laboratories. Additionally, WSTF is participating in the NASA Ohm Measurement Assurance Program administered by Kennedy Space Center.