2. Injury channel architecture in Q-Series dummies

Q-Series dummies are not simply scaled-down adult ATDs. Their injury channel architecture reflects the biomechanics of a child occupant: smaller masses, shorter moment arms, more compliant ribs, and a proportionally larger head. For NCAP assessment, the practical consequence is that every channel you read out of a Q-Series dummy must be traced back to a specific transducer, a specific conditioning path, and a specific channel definition in the data acquisition system. Misidentifying any of these three layers produces plausible-looking but wrong injury numbers, which is far more dangerous than a missing signal.

This section maps the architecture channel by channel: where the sensors sit, how the measurement chain is built from transducer to filtered output, and how each channel is defined so that the calculated injury criterion matches the NCAP protocol.

Sensor locations and what each one physically measures

The head of a Q-Series dummy carries accelerometers arranged to resolve linear acceleration in three orthogonal axes and, depending on the variant, angular rate sensors for rotational kinematics. The linear accelerometers are mounted close to the head centre of gravity so that the measured acceleration approximates the CG acceleration without a large lever-arm correction. The head channel definition for NCAP purposes is the resultant linear acceleration, computed from the three filtered components, and the injury criterion is derived from that resultant over the appropriate time window.

The neck region uses a multi-axis load cell or a set of transducers that resolve forces and moments at the neck interface. In Q-Series dummies the neck is deliberately more flexible than in adult ATDs, and the load cell measures the occipital condyle–equivalent loading: axial force, shear force, and bending moment in the sagittal and lateral planes. The channel definitions here are the neck bending moment and the neck tension/compression, each with its own filter class and its own criterion.

The chest carries deflection measurement, typically through a rib deflection transducer that outputs a displacement proportional to sternal-to-spine compression. Some Q-Series variants add chest acceleration for the acceleration-based criterion. The abdomen channel uses a similar deflection principle but with a different transducer geometry and a different allowable deflection, because the abdominal content of a child is far more vulnerable to penetration than to acceleration. The pelvis carries a load or acceleration channel depending on the variant, used to assess pelvic loading and to support the overall restraint interaction assessment.

A useful mental model: head and chest acceleration channels answer "how hard was the occupant decelerated", while neck, chest deflection, and abdomen channels answer "how much local deformation did the restraint and belt geometry impose". These are different physical quantities and must never be substituted for one another.

The measurement chain from transducer to reported channel

Every channel passes through the same logical chain, and understanding it is what allows you to diagnose a bad signal. The chain is: transducer → cable and connector → signal conditioning (bridge excitation, amplification, anti-alias filtering) → digitisation → channel definition in the DAQ software (gain, offset, polarity, filter class, sample rate) → post-processing (resultant computation, criterion calculation).

The critical point is that the channel definition is not just a label. It encodes the sensitivity in mV/V or pC per unit, the zero offset captured during the pre-test shunt or balance check, the sign convention, and the filter class. If the definition says the positive X axis points forward and the transducer is mounted rotated 180°, the reported acceleration will be inverted and the resultant will still look numerically reasonable — a classic silent failure.

Q-Series Injury Channel Architecture Head Neck Chest deflection Abdomen Pelvis Triaxial linear accelerometers near head CG → resultant acceleration channel Neck load cell: Fx, Fy, Fz, Mx, My, Mz → neck moment / tension channels Rib deflection transducer (sternum–spine) → chest deflection channel Abdominal deflection transducer → abdomen penetration channel Pelvic load / acceleration transducer → pelvis loading channel Transducer bridge / piezo Conditioning excitation, gain, AA filter Digitisation sample rate, resolution Channel definition sensitivity, offset, polarity, filter class Post-processing resultant, criterion calculation Sign convention (all channels): +X forward, +Y left, +Z upward, right-hand rule for moments. Verify transducer orientation against this convention before every test.

Channel definitions and the filter classes that go with them

NCAP protocols assign a filter class to each channel, and the filter class is part of the channel definition, not an afterthought in post-processing. Head acceleration channels are typically filtered with a CFC 1000 class filter, while neck moments and chest deflection use lower cut-offs such as CFC 600 or CFC 180 depending on the criterion. Applying the wrong filter changes the peak value and therefore the criterion, sometimes by several percent — enough to move a result across a pass/fail boundary.

A practical channel definition table for a Q-Series test looks like this. The values below are illustrative example parameters for teaching purposes, not measured data from any specific test.

Channel Transducer Filter class Derived quantity
Head acceleration Triaxial accelerometer at head CG CFC 1000 Resultant linear acceleration; HIC-type criterion
Neck moment Neck load cell, My CFC 600 Peak sagittal bending moment
Neck tension Neck load cell, Fz CFC 600 Peak axial tension
Chest deflection Rib deflection transducer CFC 180 Peak sternal compression
Abdomen deflection Abdominal deflection transducer CFC 180 Peak abdominal penetration
Pelvis load Pelvic load cell / accelerometer CFC 600 Peak pelvic force or acceleration

Verifying the architecture before the test

Before any NCAP run, the channel architecture should be verified in a fixed order. First, confirm the physical mounting: each transducer is seated, torqued to specification, and oriented according to the sign convention. Second, perform a balance or shunt check and record the zero offset for every channel; an offset that drifts between the balance and the run indicates a cabling or conditioning problem. Third, confirm the channel definition in the DAQ: sensitivity, polarity, filter class, and sample rate must match the transducer datasheet and the protocol. Fourth, run a tap or function check and confirm that the expected channel responds with the expected sign and magnitude.

A common failure symptom is a channel that reads a clean, plausible curve but with the wrong sign. This usually means the polarity in the channel definition does not match the physical mounting orientation. Because the resultant of a triaxial set is sign-independent, head acceleration can look correct while an individual component is inverted — always check components, not just resultants.

Another frequent issue is a deflection channel that saturates or clips. Deflection transducers have a limited travel range, and a belt routed too low or too high on the Q-Series chest can drive the transducer beyond its range. The symptom is a flat-topped peak; the fix is to inspect the restraint routing and confirm the transducer range is appropriate for the expected deflection, not to post-process the clipped signal.

Once the architecture is verified, the channel definitions become the contract between the test and the injury assessment. Every criterion computed later — head, neck, chest, abdomen, pelvis — depends on the chain being correct at the definition stage. Treat the channel definition table as a controlled document for each test series, and re-verify it whenever a transducer, cable, or DAQ configuration changes.

← Previous 📖 Contents Next →