Discriminating Sensors

There are two Discriminating Sensors in the SIR System: the Forward Discriminating Sensor and the Passenger Compartment Discriminating Sensor. The Passenger Compartment Discriminating Sensor is contained in the same housing as the Arming Sensor. This assembly is referred to as the Dual Sensor. Although the Arming Sensor and Passenger Compartment Discriminating Sensor require replacement as an assembly, they are referred to independently.
The Discriminating Sensors are wired in parallel on the deployment loop's ground side (low side). These sensors are calibrated to close with velocity changes severe enough to warrant deployment. The Discriminating Sensors consist of a sensing element, normally open switch contacts and a diagnostic resistor. The sensing element closes the normally open switch contacts when vehicle velocity changes are severe enough to warrant deployment.
A diagnostic resistor is connected in parallel with the normally open switch contacts within each Discriminating Sensor. These parallel resistors supply the ground path for the current passing through the deployment loop during normal non-deployment conditions. This small current flow results in voltage drops across each component within the loop. The DERM monitors these voltage drops to detect circuit or component faults.