Technical Terms - Keithley 2790 User Manual

Model 2790 SourceMeter

Technical terms

The following defines and explains technical terms associated with airbag inflators:
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Initiator — Pyro-technic device used to trigger the main gas charge generation
action. Sometimes referred to in classic military terms as a "squib". The term
"squib" may be used to refer to the core element of an initiator (explosive coated
bridgewire) or to the entire initiator.
Airbag inflator — The gas generating assembly, typically made of steel, contain-
ing a stored chemical or pressurized inert gas (or both), and an electrical initiator.
Hybrid inflator — An inflator that uses both pressurized gas and a chemical reaction
to generate the gas charge for bag inflation.
Airbag or Airbag module — The fully functional device including initiator, inflator,
textile bag and mounting frame (or enclosure).
E-check — Industry standard term for electrical testing of airbag inflators and
modules. Consists of two basic resistance measurements:
– Test continuity of the bridgewire (typically 2 to 3 ohms) using a constant current
method (typically 10 to 50mA).
– HIPOT test — Measure the insulation resistance (≥100MΩ) between the
bridgewire and the inflator housing using an applied voltage (typically 500V).
HIPOT — Used in this manual to describe the high resistance measurements made
using high voltage. The intent is not to break down the insulator, but to measure the
leakage current that flows through the insulator.
Body check (contact check) — Prior to HIPOT testing, connections to the inflator
housing must be verified. This is necessary because an open connection would
result in a reading that appears to be the resistance of the insulator, but would
instead be a high resistance reading that is the result of an open circuit.
Shorting clip (shunt bar) — For handling and transport safety against ESD
(electro-static discharge) or other accidental discharge, every inflator module has a
spring loaded clip that shorts the initiator/squib pins together when a connector is
not installed. The connection cables also include shorting clips since many inflator
modules have cables attached when manufactured such that the open end of the
cables also have shorting clips. These clips are pneumatically pushed open during
E-check testing just after the clips resistance (as a short) is measured.
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