Design and Validation of a Fail-safe Digital Igniter tester for Pyro initiator health measurement

Pyro initiators (squibs) are reliable elements meant for staging events in launch vehicle, satellite, ballistic missile applications. The health of the initiator system is assessed by safely measuring the resistance of the bridge wire element. This paper details a simple technique to safely and reliably measure the resistance of this bridge wire in igniter assembled condition. A ratiometric technique is employed which ensures that the measurement technique is independent of most of the circuit parameter variations. The voltages developed across the measuring line are fed as input to an Analog to Digital converter (ADC) and the output is displayed using low current displays. The circuit is capable of operation from a single AA cell of 1.5V, making it a low-voltage, low-power device. The ADC and integrated display is powered using a charge-multiplication technique, which ensures that the output current level are orders of magnitude below the No Fire Current (NFC) levels of the squib. Failure mode tests have been carried out extensively and the circuit is fail-safe even in case of multiple component failures. The circuit has been tested for various conditions and the worst case non-linearity is within 0.08% in Standard Room Condition (SRC) and within 0.2% under all environmental conditions.