Automation of the 27.1 kN Dead Weight Machine at NIST Kevin Chesnutwood, Samuel Ho NIST Mass and Force Group Stop 8222, 100 Bureau Drive Gaithersburg, MD

The Constitution of the United States Sect. 8. The Congress shall have power... To coin money, regulate the value thereof, and of foreign coin and fix the standard of weights and measures;

Unique Facilities at NIST Serve the Nation Mass Standards Facility –Houses U.S. National Prototype Kilogram –Custom environment with world-class measurement capability 4.44 MN Force Deadweight Machine –Largest in the world - all other large deadweight machines are traceable to this one Small Force Lab –World’s first laboratory for the realization of traceable forces in the mN to pN ranges.

Force Metrology Group Maintains and disseminates the unit of force Provides calibration services & special tests Serves as the technical arm of NCWM; performs type evaluation tests (NTEP) Participate in international key comparisons Provides leadership in national & international standardization work Performs R & D

Mechanical Metrology is Critical for the Technological World Customers Secondary Cal Labs & Instrument Manufacturers Aerospace Industry Federal Agencies & U.S. Military Power Plants / Nuclear Industry BIPM & National Metrology Institutes State W & M Labs Pharmaceutical / Biotech / Chemical NIST Divisions Fundamental Constants Automotive / Construction / Heavy Equipment

Force Metrology Laboratories Cross-Section Showing Six Deadweight Machines NIST Engineering Mechanics Building (202)

CAD Model of the 27.1 kN Machine

CAD Model Highlighting Design and Operating Principles of the Machine

Photo of the 27.1 kN Machine at the Laboratory Level

Photo of the Weight Stack and Hydraulics (below lab level)

Goals of the Project To automate and upgrade the only remaining non automated dead weight machine at NIST. Use current technologies and methods that would be able to serve as a model to upgrade the older automation systems. Have the user interface and control upgraded to a current software that will have longevity. Automate the full range and capabilities of the machine. Avoid custom control boards and circuitry. Be compatible with our current and future high precision DVM’s used in ratio calibrations.

Automation challenges 22 separate switches to control the loading and unloading of the weights (120 VAC) 23 indicator lights that show the status of each weight (loaded or unloaded) (24 VAC) 60 cam roller switches that determine the weight status and control the indicator lights When raising or lowering the weight frame, the height has to sensed in a non contact manner. Must be able to stabilize the weight frame shaft while changing loads. Had to keep “manual mode” operational. Software had be able to interface with user as well as control and monitor machine operation.

Photo of Operator’s Console Used in Manual Operation

Photo of Terminal Block Used to Integrate the “New with the Old”

Photo of USB Controller Board (right) and 3 High Voltage Boards (left)

Photo of Frame Height Indicator (used in manual operation)

Photo of Infrared Shadow Sensor Initially Used to Sense Machine Frame Height

Photo of Laser Measurement Sensor Currently Used to Sense Machine Frame Height

CAD Models of Snubber System

Sample Front Panel Display Using LabView

Other Modifications and Additions to the Dead Weight Machine Motor starter/control for the jack screw assembly was replaced Various lockouts and safety features were added using both hardware and software. Diagnostics added to the graphical user interface

Conclusions Automation system is being used as a model to upgrade our other systems. “Off the Shelve” components keeps design simple and costs reasonable. No modification to any part of the calibrated assemblies of the dead weight machine; meaning no recalibration of the masses. Automated split frame capability allows use of the full measurement range of the machine. Software platform should exist well into the future. Manual operation is still possible for proving ring or loop dynamometer calibrations. Future web access to check status, examine test data, and/or remotely control machine during overnight or weekend testing.