Due to their unique working principle and system design, Harmolign systems do not require any scheduled calibration.
Harmolign has an electro-optical camera that views a set of light emitting targets and thus determines the set of targets’ position in space – doing this for two or more sets of targets simultaneously enables the calculation of their relative position and orientation. If the relationship between a set of targets (a LED Pad) and a mechanical interface – such as the locating features of a LRU tray – is known, the orientation of that interface can be calculated. The LED Pad and the mechanical interface or adapter makes up an LRU PHP (Platform Harmonization Pad).
To measure correctly, Harmolign therefore relies on correct characterization of (1) the camera – meaning that the light propagation errors in the lens/sensor system are accurately known – and (2) the relationship between each set of light emitting targets and the corresponding mechanical interface – meaning that the position of each PHP target relative to the mechanical interface is correctly known.
Harmolign is designed with a very robust BIT system exploiting the unique possibilities for self-checking that follows from the above. For example, since there are 8 targets on each PHP, the correctness of the camera characterization is tested for every measurement taken – without the correct characterization, it is impossible to accurately fit all 8 targets into the same image. If a fit is not possible, then either the camera is bad or the set of targets on the PHP has been damaged, and testing another PHP will help determine the root cause.
Above and beyond the robustness of the BIT system where the absence of any error message indicates consistent system accuracy, it is of course necessary to be able to prove positively that the system measures accurately. Harmolign systems therefore typically include a compact collapsible ‘master jig’. The jig is referred to as the LTR – LRU Tray Replicator. This jig normally contains a separate set of 8 fixed targets, and replicates the mechanical interfaces of all units to be boresighted. Prior to shipment, each PHP is inserted into the LTR and the relationship between the targets of the PHP and those of the LTR is recorded and stored on the system.
At any time, it is therefore possible to verify system performance end-to-end by simply inserting the PHPs into the LTR and having system software compare the present measurement with that stored initially. From the above follows that a match is only possible if both the camera and the PHP (as well as the LTR) are unchanged from the as-shipped condition.
LTR usage is required when instructed by the BIT system – e.g. if one of the system’s on-board computer-read shock indicators are tripped – and can also be required on a by-calendar or by-use basis as determined from the operational environment.
Consequently, the availability of the LTR means the Harmolign system requires re-characterization only on-condition, never on-calendar, and the condition is failure of the LTR verification process.
If the LTR verification should ever show a unit in need of re-characterization, this is a specialist task, but can be carried out on-site.