3. Dummy anatomy and instrumentation

Before any Q-Series child dummy is installed in a sled, buck, or crash rig, the technician must be able to read the dummy as a measurement system rather than as a passive mannequin. Every external segment — head, neck, thorax, abdomen, pelvis, and limbs — is a mechanical structure with a defined mass, a defined joint stiffness, and one or more embedded transducers whose outputs are interpreted against a channel map. Positioning checks fail most often not because the dummy is placed badly, but because the instrumentation is misunderstood: a load cell is assumed to measure what it does not, a channel is zeroed at the wrong reference, or a cable is routed so that it preloads a joint. This section establishes the anatomy-to-channel relationship that the rest of the installation procedure depends on.

Segment architecture and what each segment measures

The Q-Series child dummy family is scaled to child anthropometry, and each segment is built around a rigid or semi-rigid internal structure covered by deformable padding and a vinyl or urethane skin. The head is a rigid shell with an internal cavity that carries accelerometers and, depending on configuration, angular rate sensors. Because the head is treated as rigid, its instrumentation measures the kinematics of the head centre of gravity, not deformation. The neck is a flexible column of butyl or comparable elastomer discs bonded between end plates; it is a structural element, not a transducer, and its behaviour is characterised by static and dynamic bending tests rather than by an installed channel.

The thorax is the most heavily instrumented region. It contains chest deflection measurement — typically a spring-loaded or IR-based displacement sensor bridging the sternum and the spine box — plus accelerometers mounted on the spine box and, in some configurations, on the sternum. The abdomen carries a force or pressure sensing element that responds to belt and airbag loading, and the pelvis carries accelerometers and, where specified, iliac or pubic force transducers. The limbs carry load cells at the joints or at the segment interfaces: upper-leg and lower-leg load cells measure axial and shear loading transmitted through the femur and tibia, and arm load cells, where fitted, capture shoulder and elbow loading.

Reading the instrumentation as a signal chain

Each transducer feeds a conditioning path: strain-gauge bridges and piezoelectric elements require different excitation and filtering, and the conditioned signal is digitised and mapped to a named channel in the data acquisition system. The figure below shows the segment-to-channel relationship for a representative Q-Series configuration, including the measurement axes and the physical reference points that matter during installation.

Why the zero reference is a positioning issue

The most consequential instrumentation detail during installation is the zero reference. Accelerometers are zeroed with the dummy in its installed, pre-test attitude so that the gravity component on each axis is captured as the offset. If the dummy is later re-oriented — for example, reclined to a different seat-back angle — without re-zeroing, every acceleration channel carries a bias equal to the change in the gravity projection. For a ±500 g accelerometer, a 10° attitude change produces roughly 0.17 g of apparent acceleration on the affected axis, which is small but not negligible when integrated into injury criteria. The practical rule is: zero after final positioning, not before.

Load cells follow a different logic. Limb load cells are zeroed with the limb hanging free or supported so that no external load passes through the cell; any preload from a cable, a suit, or a fixture becomes a permanent offset. Chest deflection sensors are zeroed at the unloaded fit between sternum and spine box, and the zero must be re-established if the thorax is opened or the sensor is reseated. Abdomen force sensors are zeroed with the belt routed but not tensioned. In each case, the zero is a statement about the mechanical state of the dummy at the moment of zeroing, and the installation procedure must reproduce that state exactly.

Channel map and cable routing as installation constraints

A working channel map for a Q-Series installation typically looks like the following. The channel names are illustrative of a representative configuration and should be replaced with the actual map supplied with the dummy.

Cable routing is part of positioning because cables are mechanical elements. A cable that is too short will preload a joint as the dummy settles into the seat; a cable that crosses a belt path will be pinched and will produce a spurious force spike at the moment of belt loading. Route signal cables along the posterior or lateral surfaces, secure them with low-mass ties at intervals that do not cross joint centrelines, and leave a service loop at every articulation so that the cable does not become the stiffest element in the load path. After routing, re-check the zero of every load cell: a shift in the zero after cable installation is direct evidence of preload.

Verifying the instrumentation before the test

A short static verification sequence catches most instrumentation faults before they contaminate a run. With the dummy fully installed and zeroed, apply a known gentle manual load to each limb in the measurement direction and confirm that the corresponding channel responds with the correct sign and a plausible magnitude; release and confirm the channel returns to zero within its noise band. Tilt the head a few degrees and confirm the accelerometer channels change consistently with the gravity projection. Press the sternum inward by a measured amount and confirm the chest deflection channel reads that displacement. If a channel does not respond, does not return to zero, or responds with the wrong sign, resolve it before proceeding — a reversed axis or a stuck channel is far cheaper to find now than after a destructive test.

Finally, record the as-installed state: zero offsets for every channel, cable routing photographs, and the attitude at which zeroing was performed. This record is what allows a later reviewer to distinguish a genuine dummy response from an installation artefact, and it is the reference against which any post-test inspection of the dummy is judged.