2D and 3D IRTRACC configurations have been introduced to try to describe the true position of a point in space relative to an ATD referenced coordinate system. The idea is to try to more reliably record oblique impacts where displacements can be quite large in reality, but would not necessarily be captured by a uniaxial displacement device as it would simply be pushed sidewards.
2D and 3D IRTRACC's do this by having a different set of calibration values to enable them to measure distance (sometimes called "absolute length", "pivot point to pivot point" or "radius") relative to a fixed point in the dummy, which when combined with the angle(s) allow a calculation of displacement at the point of impact on the ATD.
2D IRTRACC's consist of 1 distance and 1 angle measuring channel.
3D IRTRACC's consist of 1 distance and 2 angle measuring channels.
IRTRACC's without associated angle channels are more traditionally used to directly measure displacement using the "tube in - tube out" calibration factors.
IRTRACC distance and angle channel(s) allow the description of the displacement in what is called a "polar coordinate system", and post processing algorithms allow the conversion of this distance and angle measurement(s) into the more familiar SAE J211 X,Y,Z Cartesian coordinates.
This is a typical "tube in- tube out" displacement calibration result :
Note how the measured displacement is not related to the local spine coordinate system and the linearized output has a -ve slope (the blue line)
This is a typical "radius" calibration result :
Note how now the distance is related to the local spine coordinate system and the linearised output has a +ve slope (the blue line) .
Also note how the ISO code is DC not DS and the direction is 0 [directionless]. This is critical for post test analysis software so that the right mathematics is applied.
With 2D and 3D IRTRACC's calibrated to measure distance, the starting values of these channels when viewed in real time or pre T0 in a data set, will be at the nominal design position of the ATD. This allows the user to readily verify that all is well with the set up prior to a test and will highlight permanent channel deformations that need investigating.
Here is a side by side comparison of "displacement" and "radius" calibration values :-
Because TDAS Control is a legacy product, DTS has had to try to implement the calibration factors for a radius calibration into the well known and existing SIF user interface that has always supported the traditional displacement calibration values. Unfortunately the linearization algorithm was written in such a way that it always forced a -ve calibration factor as per the slope of the displacement graph in order for the mathematics to work out.
In order to support radius calibration the calibration factor needs to be entered as a counter intuitative NEGATIVE number so that the linearization algorithm forces a negative value and a double negative becomes a positive as per the radius calibration graph.
This would be what you would enter to support the radius calibration values as above :
NOTE : the sensitivity value is entered as mV/mm so the Inverse CF V/mm value is used from the cal sheet and multiplied by 1000 to convert from V/mm to mV/mm
The full entry is :
Here is another way to view the information to be input :
The other part to consider with 2D and 3D IRTRACC's is the angle sensor entry. In order for the distance mathematics to work, the default starting position and sense of the angle channel is critical and dependant on where and in which ATD type the 2D/3D IRTRACC is mounted.
You should refer to the IRTRACC calibration report for an overview of the angle entry values based on ATD type and mounting position.
This is a typical 2D IRTRACC calibration report :
It tells you that for a WSID 50th set up for a Left hand side impact, the angle SIF sensitivity entry will be -3.169mV/V/deg and the initial engineering unit offset value should be 93.18 deg.
If the sensor was mounted in a Q10 set up for a frontal impact then the sensitivity would still be -3.169mV/V/deg but the initial engineering unit offset value should be 3.178 deg
These values are not quite the nominal 90deg (for side impacts) and 0 deg (for frontal impacts) to the physical mounting in the ATD at the design position.
It gets even more complicated in some circumstances where the orientation of the sensor has to be upside down. In these circumstances note how both the polarity of the sensitivity and the polarity of the initial angle both change :
The best way to handle this is to have multiple SIF entries for the angle based on ATD type and orientation otherwise it is far too easy to use the wrong angle sensitivity and start position.
To make sure that you have it all correctly set up it is always advisable to follow the SAE J211 dummy manipulations described in the ATD manual to verify that not only is the starting position correct but that the channel moves in the right direction when the ATD is manipulated.
This is an example of the WSID 50th rib entries that clearly define what to expect :
[All sensor calibration and ATD manual information is curtesy of Humanetics ATD inc.]