Impact Sensor: Description and Operation

DUAL POLE ARMING SENSOR
The dual pole arming sensor is a protective switch located in the high side(power side) of the deployment loops. The dual pole arming sensor is calibrated to close at low level velocity changes(lower than the discriminating sensors).

This ensures that the inflator modules are connected directly to the "36 VLR" outputs of the DERM or "Ignition 1" voltage when any discriminating sensor closes.

The dual pole arming sensor consists of: a sensing element, two sets of normally open switch contacts, diagnostic resistors and diodes. The sensing element closes both sets of switch contacts when the velocity of the vehicle changes at a rate indicating a potential need for deployment.

Two of the diagnostic resistors are connected in parallel with the switch contacts. This allows a small amount of current to flow through each of the deployment loops during normal, non-deployment operation. This current flow results in voltage drops across each component in the deployment loops. The DERM monitor these voltage drops to detect circuit or component malfunctions. There are two additional diagnostic resistors within the dual pole arming sensor which allow the DERM to monitor the voltage supplied to the high side of the deployment loops. These monitored voltages are used by the diagnostic logic of the DERM to make a more precise determination of the actual deployment loop malfunction.

The diodes within the dual pole arming sensor provide isolation between the "36VLR" outputs of the DERM and the vehicle electrical system "Ignition 1" voltage. The presence of the diodes prevents a direct continuity measurement through the dual pole arming sensor resistors to terminals"3","4" or "5".

DISCRIMINATING SENSORS
The discriminating sensors are protective switches wired in parallel on the low side(ground side) of the deployment loops. These sensors are calibrated to close with velocity changes which are severe enough to warrant deployment.

The discriminating sensors consist of a sensing element and normally open switch contacts when the vehicle velocity changes are severe enough to warrant deployment.

A diagnostic resistor is connected in parallel with the switch contacts within the LH forward discriminating sensor and RH forward discriminating sensor. These parallel resistors supply the ground path for the current passing through the deployment loops during normal, non-deployment operation. This current flow results in voltage drops across each component within the deployment loops. The DERM monitors these voltage drops to detect circuit or component malfunctions.