1-8 Model 2790 SourceMeter® Switch System User’s ManualBridgewire testThe air bag inflator has two terminals connected to a bridgewire, which is coated with aprimer that ignites when sufficient current passes through the wire. The bridgewire’s resis-tance is typically from two to three ohms (2Ω being the most common). To avoid unintendedignition, the level of test current applied is generally 50mA or less.As shown in Figure 1-3, a fixed current is sourced through the bridgewire. The voltageacross the bridgewire is then measured by the DMM of the Model 2790.Figure 1-3Bridgewire testingWith the low ohms math function selected, the RBRID reading can be read directly fromthe display of the Model 2790.I-source readback — Before performing the bridgewire test, you can verify the actualcurrent flowing in the test circuit by using the I-source readback circuit.NOTE A more accurate ohms reading can be achieved using the Ω4 function of theModel 2790 (1mA fixed). See Section 6 for details.2790DMMvISOURCEBridgewireUnderTest(RBRID )RBRID = VMEASISOURKeithley 2790 SourceMeter Switch SystemKeithley7751,7752,or 7753Module
