The best Goniometer System is useless if the user can not align the system properly !

Too often, the discussion on the “performance” of light scattering systems is reduced to a few numbers on minimum measurable molecular weight, or diffusion coefficients, the laser power or whatsoever. Although knowing the performance of ALV-Goniometer Systems, we at ALV think that there is no need at all to avoid such a discussion, we still believe that such a discussion is of little help to judge for the quality of a particular device. Even worse, it almost always omitts the problem of “getting there”. Having a goniometer system being able to principally perform a DLS/SLS measurement on a, say very diluted, small polymer is one thing - getting around the obstacles to actually ensuring the goniometer to at the moment being able to perform exactly this measurement is a completely different problem.

Quite obviously, it is of little help for the user to have a goniometer system that is principally capable of performing a certain measurement, but not having any measure to reproducably ensuring this. Most reader have already noticed - the problem is the alignment of the goniometer, the alignment procedure and the potential checks for a sufficiently good alignment.

The alignment of a goniometer system can become necessary for many reasons, the most well known are

• after a laser replacement (aka “worst case scenario”)
• because of temperature changes in the environment
• because of temperature changes in the sample temperature
• regularly at certain periods, because of “standard use” of the instrument

The good news about ALV-goniometer systems is, that they are designed to be exceptionally little susceptible against temperature changes in both, environmental changes as well as sample temperature changes. As long as these are within the limits set (+/- 2°C for the environmental temperature and the specified temperature range for the sample temperature), there simply is no change in the alignment status of the instrument. Along with this, ALV goniometers keep their alignment stable for months and the usual “re-alignment” period can be set as large as once per year. But even such rather long realignment periods do not prevent the user to once in a while being the one actually performing the alignment of the goniometer system.

The ALV Approach to a “deterministic” Goniometer System Alignment

The ALV approach to a “deterministic” Goniometer System alignment is based on a very simple principal - if you can not measure it, don’t use as alignment parameter ! Even in reality, ALV does in fact stick to that principle as much as possible !

Without special tools, enabling the user to precisely measure and reproducably set certain adjustment screws or whatsoever to a certain position, ALV would rate the alignment procedure as being “probabilistic” - sometimes the user will succeed in obtaining a good alignment, sometimes not - in all cases he/she has no idea why it did or did not work. With the proper tools, a deterministic and algorithmic way of using the adjustments of the goniometer system can be found, and even better, since this anyway leads to a systematic scheme, a computer can greatly help the user in doing so, specially remembering numbers, or solving sets of linear equations, or, or ... Thus the three major ingredients of a deterministic alignment are :

• appropriate tools and measuring devices
• de-coupled adjustments (which is that turning one parameter will not change the other !)
• additional software help

All these principles are part of the ALV-Goniometer Systems, numerous tools, dial-gauges, micrometers etc. help the user to align the goniometer system in a few hours after the “worst case scenario” - even less for small realignments. Furthermore, these tools can be used any time to check if a realignment at all - or, if unexpected results are measured by the goniometer system, if these are caused by a misalignment or have other sources. The ALV-WinAlign Software allows even unskilled users to align the goniometer system - step by step guidance with figures about where to find which screw and how to turn it etc. makes it almost impossible to not obtain a good alignment in the end.

 

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