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20 cies were addressed, and the upgraded device was accepted in December, 2006. 3.2.3 Medical Device Testing Services First Article The Medical Device Testing Services (MDTS) first article is shown in Figure 15. The equipment is relatively small. It con- sists of (1) a main wheeled cabinet (26 in. wide by 76 in. high by 24 in. deep) that houses the test chamber, the hydraulic pump, the hydraulic actuator, and associated control elec- tronics; (2) a separate heat exchanger (16 in. wide by 23 in. high by 20 in. deep) that provides temperature control for the test cell; and (3) laptop computer for controlling the machine and collecting and analyzing test data. The heat exchanger is Figure 13. Interlaken specimen mounted under the laptop computer table in Figure 15. An interesting extensometer system. feature of the MDTS SPT is the hydraulic system operates on 115 V AC power, and the hydraulic pump only operates intermittently, which makes the unit very quiet during oper- compliance tests detailed in Version 2.0 of the specification ation. The heat exchanger requires single phase 208230 V were performed. Table 9 summarizes the items included in AC power. The unit also requires compressed air to raise and the specification compliance testing. The specification com- lower the test chamber and apply confining pressure. pliance testing revealed several deficiencies with the upgraded Figure 16 shows the MDTS SPT with the test chamber equipment summarized in Table 10. Most of the deficiencies open, and a specimen inserted for confined testing. The test were related to the control and analysis software. Table 10 chamber is relatively small, only 10 in. in diameter by 21 in. also summarizes the changes made to resolve the deficiencies. high. The reaction posts are located in an awkward position, Substantial effort was expended by both the research team making installation of the instrumentation on the specimen and Interlaken to resolve the deficiencies. All of the deficien- for dynamic modulus testing difficult. The test cell heat exchangers and associated fans are mounted in the top of the test chamber. The test chamber is insulated; a sight glass and lighting are provided to allow the operator to view the speci- men during testing. The chamber is opened and closed by a manually controlled pneumatic actuator located at the back of the machine as shown in Figure 17. It is locked in the closed position by a manual ring locking mechanism that has posi- tion switches that are interlocked with the pressure and load control. The specimen mounted deformation system consists of two magnetic LVDT extensometers mounted 180° apart as shown in Figure 18. Each extensometer includes two very flexible springs that allow only vertical movement of the ends. Each extensometer includes a pin that centers the measuring system. When the pin is released, the extensometer is acti- vated. These extensometers are similar to those developed by Interlaken. This deformation measuring system is the third system that was developed by MDTS for the SPT. The other two systems did not function properly during the ruggedness testing. To quickly and accurately mount the glued gage points to the specimen, MDTS designed the gluing apparatus shown in Figure 19. This system has pneumatic actuators that press the gage points against the specimen at the correct gage Figure 14. Interlaken gluing apparatus. length at the center of the specimen.
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21 Table 9. Summary of specification compliance tests. Specification Item Section Method Assembled Size 4.4 & 4.6 Measure Specimen and Display Height 4.4 Measure Component Size 4.7 Measure Electrical Requirements 4.5 & 4.6 Documentation and trial Air Supply Requirements 4.8 Documentation and trial Limit Protection 4.9 Documentation and trial Emergency Stop 4.10 Documentation, visual inspection, trial Loading Machine Capacity 5.1 Independent force verification Load Control Capability 5.2 5.4 Trial tests on asphalt specimens and manufacturer provided dynamic verification device. Platen Configuration 5.5 Visual Platen Hardness 6.1 Test ASTM E10 Platen Dimensions 6.2 Measure Platen Smoothness 6.3 Measure Load Cell Range 7.1 Load cell data plate Load Accuracy 7.2 Independent force verification Load Resolution 7.3 Independent force verification Configuration of Deflection Measuring 8.1 Visual System Transducer Range 8.2 Independent deflection verification Transducer Resolution 8.3 Independent deflection verification Transducer Accuracy 8.4 Independent deflection verification Load Mechanism Compliance and 8.5 Measure on steel specimens with various degrees of lack of Bending parallelism Configuration of Specimen 9.1 Visual Deformation Measuring System Gauge Length of Specimen 9.1 Measure Deformation Measuring System Transducer Range 9.2 Independent deflection verification Transducer Resolution 9.3 Independent deflection verification Transducer Accuracy 9.4 Independent deflection verification Specimen Deformation System 9.5 Trial Complexity Confining Pressure Range 10.1 & 10.5 Independent pressure verification Confining Pressure Control 10.2 Trial tests on asphalt specimens Confining Pressure System 10.3 & 10.4 Visual Configuration Confining Pressure Resolution and 10.5 Independent pressure verification Accuracy Temperature Sensor 10.6 & 11.4 Independent temperature verification Specimen Installation and 9.5, 10.7 & Trial Equilibration Time 11.3 Environmental Chamber Range and 11.1 Independent temperature verification Control Control System and Software 12 Trial Data Analysis 13 Independent computations on trial test Initial Calibration and Dynamic 14 Certification and independent verification Performance Verification Calibration Mode 14.6 Trial Verification of Normal Operation 15 Review Procedures and Equipment On-line Documentation 16.1 Trial Reference Manual 16.2 Review
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22 Table 10. Interlaken deficiencies and solutions. Deficiency Solution Slow temperature recovery. Modified the temperature control software to switch control from the test chamber probe to the bath probe when the chamber is opened, then back to the test chamber probe when the chamber is closed. Cooling fluid leaks. Replaced plastic hose clamps with steel band hose clamps. Units for temperature control. Modified software to use both U.S. customary and SI units. Test chamber binding. Lubricated actuator shaft and realign chamber. Test chamber air leaks. Added temporary seal to affected areas. 0.01 Hz loading for dynamic Modified software to allow user to test at 0.01 Hz loading. modulus. Irregular first cycle data during Modified software to collect additional cycles that are not stored. Only the dynamic modulus testing. last 10 cycles are stored and analyzed. Incorrect computation of dynamic Modified software to correct computations. modulus data quality statistics. Poor dynamic load control at high Added a tuning algorithm to allow user to develop and store templates with temperatures. servo-hydraulic gains. Software occasionally crashes Modified strain limit shut down algorithm. when maximum strain is reached during flow number testing. Incomplete documentation. Provide required documentation Final design, fabrication, and shop testing of the MDTS rized in Table 9 was performed. The specification compliance SPT required approximately 18 months. MDTS was given testing and the ruggedness testing revealed several deficien- authorization to proceed with the machine on February 6, cies with the equipment, which are summarized in Table 11. 2004. The machine was delivered on September 14, 2005. Most of the deficiencies were related to the control and analy- Upon delivery, the specification compliance testing summa- sis software. Table 11 also summarizes the changes made to Figure 15. Overall view of MDTS SPT. Figure 16. Open test chamber for the MDTS SPT.