In recent years, a lot of the conversation around advancements in x-ray fluorescence (XRF) technology has related to the detector systems. XRF analyzers are offered with two major types of detector technologies…the more traditional proportional counter detectors and newer solid-state detectors. Unfortunately, even though proportional counter may be a great choice for some applications, it is often not discussed because the XRF sales company doesn’t offer it or are more focused on promoting the newer, more hyped, technology.
However, proportional counter detection systems still have a place and organizations looking to purchase an XRF should answer an important question before moving forward with any investment…“What detector system is best for our situation and testing goals?“
Background on XRF Detector Systems
When x-ray fluorescence (XRF) technology was first made available for coating thickness measurement needs they featured proportional counter detector tubes. However, the industry saw the potential to expand the application reach of XRF and began introducing analyzers that used solid state detectors. Two types of these solid state detectors offer higher resolution and potentially faster measurement times; Silicon PIN Diode Detectors (Si-PIN) and, more recently, Silicon Drift Detectors (SDD). These new detector technologies were initially featured in XRF analyzers built for elemental analysis (RoHS testing, geological, etc) while proportional counter remained the go-to for metal finishing quality control.
Manufacturers of XRF recently began looking to the newer solid state detectors for plating thickness applications. The higher resolution of Si-PIN and SDD can be beneficial for very thin coatings (think ENIG, ENEPIG, coatings under 2u”, etc) but proportional counter systems still have a place in coating thickness measurements – and offer critical benefits. It’s important to know if…an XRF manufacturer only offers solid-state based analyzers because discussing your goals with organizations that offer both styles can help you learn about all the unbiased options and benefits.
Benefits of Proportional Counter Systems
The major benefit of proportional counter detectors is their lower cost. When compared to an XRF with a high quality Si-PIN or SDD, the proportional counter system itself will be a lower initial investment and future repairs will also be lower in cost. Note the reference to ‘high-quality’ Si-PIN or SDD, which may not always be offered…systems with lower quality solid state detectors may have a competitive list price but more detector issues in the long-term plus, potentially, not as good a resolution which defeats the main purpose of a solid state detector.
In addition to lower costs, proportional counter detectors will typically provide better longevity. As we’ve noted in the past, a bad working environment can negatively affect an XRF but we’ve seen that to be especially true for units with Si-PIN or SDD technology…specifically, they appear to be more susceptible to heat and humidity than a proportional counter detector. This durability ties in with the component cost and long-term benefits that proportional counter can offer.
When a Proportional Counter Should Be Considered
As previously noted, solid state detectors (Si-PIN and SDD) were first offered for elemental analysis and remain the best option for those applications. However, their application reach expanded to where they can be considered for some coating measurement needs. Organizations can now consider solid-state detectors when looking to measure thin film coating measurements (ENIG, ENEPIG) or coatings where resolution could benefit accuracy (multi-layer stacks, etc).
That being noted, proportional counter still offers excellent performance (with the benefits noted above) for more typical coating applications and can still be considered for many thin coatings or complex multi-layers. Each individual application will have a different threshold for where proportional counter detectors will offer better accuracy…the threshold being where thicker coatings should be measured with a proportional counter detector and thinner ones should look to a solid-state detector.
While coating measurements occur for many applications and at a variety of organizations, it’s important to note that any general metal finishers will often be plating thicker coatings and that is just one reason metal finishers should really consider the benefits of proportional counter based XRF analyzers.
Bottom Line (especially for general metal finishers)
Any organization looking to add an XRF to measure coating thickness should certainly consider the detector system options – taking into account the finishes to be measured and the benefits of each detector.
Remember too, that some XRF manufacturers only offer Si-PIN and SDD based systems…so, they won’t point out when proportional counter would be a better fit. However, other XRF analyzer sales companies, like distributors of Hitachi High-Tech (Eastern Applied Research Inc being one), offer both types of detector tube options. Some new analyzers like the Hitachi XStrata920 are even offered with the buyers choice of detector tube.
So, discuss your specific testing goals, and even test out specific applications by submitting samples, etc. This can help identify when the benefits of proportional counter will be a long-term benefit to your company (while meeting your performance needs of course).
Contact an XRF Application Specialist from Eastern Applied Research
to discuss your situation and the pro’s/con’s of various XRF Analyzers.
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