1-6 Model 2790 SourceMeter® Switch System User’s ManualInflator testsThere are three primary tests for an inflator:• Shunt bar test• Bridgewire test• Insulation resistance (HIPOT) testNOTE Interlock – The three primary tests can only be performed if the interlock of the7751/7752/7753 module is enabled. With interlock open (disabled), the I-sourceof the 7751/7752/7753 module and the V-source of the 7751/7753 module aredisconnected from the switching module matrix. Details on the interlock are pro-vided in Section 5.The following information provides an overview of the three tests that are usedto test an inflator. The actual detailed procedures for these tests are provided inSection 5.Shunt bar testNOTE A shunt bar test is typically tested again after all other inflator tests are completed.As a final test, it verifies that it is safe to install the inflator in a vehicle.A shunt bar (shorting clip) is used to short the bridgewire(s) to prevent accidental ignitionwhen handling or installing the inflator. However, an oxide can form between the shuntand the inflator terminals. It is this high-resistance oxide that diminishes the ability of theshunt bar to act as an effective short across the bridgwire(s). Without a good contact short,detonation could occur. The measured resistance of a shunt bar is typically between 10 to100mΩ.One method used for the shunt bar test is shown in Figure 1-2. In this case, the dry circuitmode of the 7751/7752/7753 clamps voltage at 20mV (1mA maximum) for the constanttest current of the I-source. This low voltage will not pierce the oxide. With the low ohmsmath function (SxIohms) selected, the RSHUNT reading can be read directly from the dis-play of the Model 2790.
