OE750: Your Questions Answered

The OE750 OES analyzer contains some of our most advanced technology and delivers excellent performance for low-level metals detection across the entire spectrum. Unsurprisingly, questions about the OE750 tend to be about the analysis technology and operational performance.

In this post, our product manager, Wilhelm Sanders, answers five common questions on the OE750 asked during our product demos.


1. Does it use PMT or CCD detector technology?

Neither. The OE750 uses state-of-the-art CMOS detectors, which are semiconductor-based sensors (as are CCD detectors). Semiconductor based systems have advantages over photomultiplier tube (PMT) systems as they cover a wider range of wavelengths and therefore elements. While PMT technology enables high detection limits at low sensitivity, each sensor can only cover a limited wavelength. This means that you’ll need several PMT detectors in a single instrument to cover a wide range of elements, and adding additional capability will mean adding extra detectors, which can be expensive or it is even not possible to add them to the optical system due to their bigger geometrical size.

As CMOS detectors have much better resolution and dynamic range than standard CCD technology, their use delivers better analytical performance, as is seen in the OE750. This means that we can cover the complete element range of interest for metals analysis: from 119nm to 766nm  – correlating to an element range from hydrogen to uranium (depending on application and matrix).

In short, the CMOS sensor gives you the advantages of both kinds of technology: you get the ultra-low detection limits and almost the sensitivity delivered by PMT with the full spectral coverage delivered by CCD.

(NB: We are planning to publish an article that goes into detail about these technologies, so subscribe to our blog [include link] if you’d like to find out more)


 2. How many samples can be tested per day?

Typical measurement times are below 15 seconds per burn for all mentioned matrices. To give a few examples:

Aluminum matrix: 14.5s per burn.

Steel matrix: 12.5s per burn.

Other matrices: 11-12s per burn.

The OE750 is designed to work in a continental shift schedule, i.e. a 24 / 7 shift coverage, and if we assume two burns per sample, then it’s entirely possible to do several hundred analyses per day.

However, maintenance will have a bearing on this. How frequently you will need to clean the spark stand depends on the matrix. For steel, we recommend cleaning after 2,000 burns, whereas for aluminum we recommend 1,000 burns. This is because the lower the melting point of the material, the more will be deposited during sparking, resulting in a shorter cleaning interval. Maintenance (and therefore downtime) of the OE750 is kept to a minimum by the direct optical light path that eliminates optical fibers. However, for heavy, continuous use, we recommend at least one service visit per year by our service team to clean and maintain the instrument.


OE750 Live Demo


3. What is the argon consumption and typical argon flow?

This will depend on how much testing you do, but if we take a couple of scenarios, we can work out the argon usage over a year.

The constant flow of argon is 12 l / h and the analytical flow is 50 l / h. Let’s say that we’re measuring steel, which gives us a measurement time of 12.5 seconds. For our first scenario, we’ll assume 100 burns per day, for 200 days of a year and the system is in standby for 24 hours. In this case you will need six  bottles of argon per year of 50 l / 200 bar.

If you measure 300 samples per day, with all other factors equal, you will need seven bottles.

We should mention that the argon usage for transparency of the optics is very low as the OE750 uses a unique mid-pressure system with a low argon flow purge. This means we can use an oil-free membrane pump which reduces the risk of contaminants entering the optics.

So with purchase of an instrument you should also consider the operating costs, which can easily make a big impact on the overall investment.


4. How long does it take to purge the optics with argon?

It depends on the initial state of the instrument. For example, for initial installation after delivery, the argon flow into the optics will take 12 hours. (What we call a full pump cycle run). However, once installed, you should keep your system in stand-by mode – which ensures the optics are always surrounded by argon.

But let’s look at scenarios where the instrument may be switched off:

A weekend shut down with argon flow
You’ll need to run a short pump cycle (takes 15 minutes) and make five measurements of a burn sample. (A burn sample, for example is RE12 in Fe base.)  This procedure is necessary to achieve a good burn spot and to reactivate the argon to the spark stand.

A weekend shut down without argon flow
Exactly as described for the with argon flow scenario above.   However, we always recommend to do a transparency check after any shut down with the provided check sample for this procedure. This check is easy to do and takes less than a minute.

Vacation period shutdown

Here you’ll need to run a long pump cycle of 12 hours, plus a transparency test and measure a burn sample to verify the burn spot.


5. Does using a boron nitride disk to reduce the spark stand hole diameter affect analysis accuracy?

Yes, it does. There are minor precision and accuracy deviations when compared with samples covering the complete 14 mm spark stand gap. This is due to interference from air entering the spark gap. The OE750 has unique jet stream technology that reduces this effect as much as possible, but as you reduce the diameter, the interference from the ambient air has more of an effect.

Another issue is that nitrogen and boron cannot be analyzed as they are part of the boron nitride disk itself. We are currently developing on an alternative to boron nitride to allow for the analysis of boron. Nitrogen, unfortunately, will remain an issue as there is simply too much coming in via the spark stand gap from the ambient air.


Find out more…

If you’d like to find out more about the OE750’s capabilities and how it can support your business, you can book a one-to-one consultation using the form below. 


Book a Demo

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Date: 28 April 2020

Author: Wilhelm Sanders, OES Product Manager

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