BACKGROUND.

TPM's will likely be produced in multiple form factors and with differing capabilities. Most TPM's will be electronic devices, which communicate via a wireless link in addition to presenting a visual indicator to the operator or technician. One TPM under consideration is the mechanical TPM made by Accu-Pressure. This TPM displays green if the tire pressure is in the acceptable range, and red if the tire pressure is 10% or more below the target. Accu-Pressure TPM's are available in a variety of target pressure settings.

PURPOSE.

The test is designed to measure the leakage rate of the TPM itself. No amount of leakage is acceptable. The test will also measure the repeatability of the devices by testing at least 100 units. It will also verify the thresholds at which the display changes.

PROCEDURES:

1. Leakage Rate
   Create a pressure vessel capable of holding 200-psi steady state pressure. Arrange the pressure vessel so that an Schrader/tire inflation fitting (provided by the engineer) can be mounted. Inlet air must be gated. Measure the internal pressure of the vessel with a suitable electronic device accurate to +/- 1 psi capable of unattended data logging.
    
   Affix an Accu-Pressure TPM to the Schrader fitting of the pressure vessel. Pressure the vessel to the pressure indicated on the cap of the TPM. Close the supply line valve to isolate the pressure vessel. Log the internal pressure of the vessel for 72 hours.
    
   Repeat the process for each of the 100 TPM's supplied by the engineer.
   
2. Accuracy
   With the pressure vessel of Test I, affix an Accu-pressure TPM to the pressure vessel. Pressurize the vessel to the TMP's rated pressure. Bleed air from the vessel at a rate of 5- psi per minute. Record the prssure at which the display goes from green to red. Compare the recorded pressures to the manufacturer's specification as a percent error.
    
   Repeat the process for each of the supplied TPMs.
    
3. Repeatability
   Use the data from Test II and calculate min, max, average, and standard deviation for the transition pressures recorded.
    
4. Thermal Cycling
   WIth the pressure vessel of Test I, affix an Accu-Pressure TPM to the pressure vessel. Pressure the system to 100 psi. Place into the Russels climate chamber and cycle from -40°F to 165°F as quickly as the chamber can cycle. Repeat the cycle five times. Repear the process for ten Accu-Pressure TPM's.
    
5. Pull Apart - Thread Failure
   The objective of this test is to determine the ultimate strength of the plastic threads in the Accu-Pressure TPM. Mount a valve stem of valve stem facsimile into the Instron material tester. Place an Accu-Pressure TPM onto the test device. Pull the Accu-Pressure unit off the threads, measuring the force required to strip the Accu-Pressure TPM. Test five units.
    
6. Pull Apart - Weld Failure
   This test is designed to study the weld integrity of the "Glass Body" to "Valve Body" joint. Fixture the Accu-Pressure in the Instron material tester so that tension is applied to the indicated weld joint. Measure the force required to rupture the unit. Test five units.

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