In this tech tip, we describe how to save a reference spectrum and a dark spectrum in the Schematic View of OceanView spectroscopy software. The Schematic View in OceanView presents data from your device(s) in a diagram format.
(more…)-
High Speed Averaging Mode Boosts SNR Performance
The new High Speed Averaging Mode improves signal to noise ratio (SNR) in Ocean SR2 and other new spectrometers using hardware-accelerated signal averaging. With better SNR comes higher quality spectra and more accurate results.
(more…) -
FAQ of the Month: Setting Data Acquisition Parameters
We describe spectral data acquisition parameters in OceanView operating software, from integration time to scans to average. Use OceanView acquisition and processing features to optimize experiment settings.
Note: Please refresh your browser if you do not see any screenshots or icons in this material.
Q: I’m getting started in OceanView and don’t understand how best to use the data acquisition parameters that are available. What do I need to know?
A: Understanding the key data acquisition parameters available in OceanView will help ensure best results for your spectral measurements. This is important even if you’re using one of OceanView’s wizards, which guide you through the steps for specific measurements (absorbance, color and so on) but still require you to input most data acquisition parameters.
Additional resources offering insight on this FAQ are available at our Glossary and via the links at the bottom of this page.
Integration Time
This is the first parameter that you will set. Integration time is the period of time over which the spectrometer collects photons and correlates with the intensity of the signal that is captured. We find that the best measurements are made when the signal intensity is between 80% and 90% of its full range. When setting integration time, be careful not to allow any pixels to become saturated, as these pixels will not provide useful data.
Quick tip: In OceanView 2.0.8 and higher versions, there’s a convenient feature that automatically selects the integration time appropriate for your setup. Activating this feature is as simple as selecting the Automatic option in the Acquisition Group Window of OceanView.
Scans to Average
This time-based averaging function specifies the number of discrete spectral acquisitions that the device driver accumulates before OceanView receives a spectrum. The higher the value, the better the signal-to-noise ratio (SNR). The SNR will improve by the square root of the number of scans averaged.
Quick tip: To convey the “true” SNR of its spectrometers, Ocean Insight reports SNR specifications without signal averaging applied.
Boxcar Width
Boxcar smoothing is a technique that averages a group of adjacent detector elements across spectral data. For example, a boxcar width value of 5 averages each data point with 5 points to its left and 5 points to its right.
The greater the boxcar width value, the smoother the data and the higher the SNR. If the value entered is too high, a loss in spectral resolution will result and peaks will become flattened. The SNR will improve by the square root of the number of pixels averaged.
Quick tip: There’s a more detailed explanation of boxcar smoothing and its trade-offs in our Glossary.
Electric Dark Correction
Many spectrometers have a small number of dark pixels. A dark pixel is an electrically active CCD detector pixel that has been physically coated to prevent any light from entering. Due to leakage, a small amount of electrons escape from the detector well even if there is absolutely no light.
To eliminate any error due to leakage, electric dark correction computes an average value of these dark pixels over 15 consecutive scans, and then subtracts this average value from all pixels in the spectrum. Although the algorithm specifies that 15 consecutive scans be averaged, the correction factor is applied as soon as the first spectrum of data becomes available. Then additional scans are averaged into the correction factor as these spectra become available. A running average of the most recent 15 scans is maintained.
The amount of electron leakage is proportional to the duration of the integration time. So, whenever the integration time is changed, the previous correction factor is discarded and we then begin to compute a new correction factor based entirely on the new integration time.
Non-linearity Correction
All Ocean Insight spectrometers are calibrated at the factory to maximize accuracy. One of the calibrations performed is to correct for detector non-linearity. This calibration consists of eight numbers used as the coefficients of a 7th order polynomial, which adjusts for the phenomenon that CCD detectors do not respond to stimuli photons uniformly as more electrons drain from the detector well. In other words, the efficiency of CCD detectors may be 30% when the well is half-full but may be only 20% when the well is completely drained of electrons.
By “efficiency” we mean the probability that an incoming photon will drain an electron from the CCD well; 100% efficiency means every incoming photon will drain one electron, while 50% efficiency means an incoming photon has only a 50% chance of causing an electron to drain. Non-linearity calibration is made by averaging together all pixels of the CCD array. Thus, we are assuming that all pixels respond about the same.
Quick tip: Detector linearity is different than absorbance linearity, which is associated with Beer’s Law.
-
Five Simple Rules for Fiber and Probe Maintenance
Ocean Optics optical fiber assemblies, probes and accessories allow users to transmit and collect light in our spectrometer setups. From off-the-shelf patch cords and custom fibers to specially engineered OEM assemblies, your fiber options are as varied as your applications. Here are some tips to ensure reliable, long-lasting fiber and probe performance.
Rule #1: Choose Wisely
Modular spectral systems are only as good as the sum of their individual parts. The same care you put into choosing a spectrometer should go into choosing a light source, the sampling optics, and the fibers or a probe. Are you measuring absorbance or reflectance? Are you measuring wavelengths below 270 nm, where UV exposure can solarize certain fibers? Where will the fiber be placed in your setup? Is the sample environment chemically harsh? Determining those criteria will help us guide you to the optimum combination of components – including fibers – that meets your needs and tolerates sample conditions.Rule #2: Handle Fiber Connectors and Terminations Carefully
Without proper care, SMA 905 and other fiber connectors can be scratched or damaged and affect measurements. On occasion, customers have even inadvertently separated the connector or ferrule from its fiber or probe assembly by pulling on the end too forcefully.Since the ends of fibers receive the most wear and tear, manufacturers design terminations with extra strain relief and boot collar protection. But just be mindful when removing end caps to use one hand to hold the fiber by the connector and the other to pull off the end cap. Ocean Optics XSR extreme solarization-resistant fibers go one step further by having an end cap that screws on to the end of the fiber — no pulling necessary.
Rule #3: Mind the Bend Radius
Although optical fibers and probes are used to move light around your spectrometer setup, there is a limit to how much bending those assemblies can tolerate. The bend radius of a fiber denotes how sharply the fiber can bend before damage occurs in the fiber. This damage can range from fiber attenuation to fiber breakage, which leads to even more dramatic light loss.That’s why it’s good practice to inspect fibers periodically to ensure that light transmission is occurring. Broken fibers stop transmitting light.
Ocean Optics reports both long-term bend radius (LTBR) and short-term bend radius (STBR). LTBR is the minimum bend radius recommended for storage conditions. STBR is the minimum radius recommended during fiber use.
Bend Radius for Visible-NIR, UV-Visible and Solarization-resistant and Extreme SR Fibers
Fiber Core Size Fiber Types LTBR STBR 50 ± 5 μm VIS-NIR, UV-VIS 4 cm 2 cm 100 ± 3 μm VIS-NIR, UV-VIS 4 cm 2 cm 113 ± 6 μm (115 μm nominal) XSR 4 cm 2 cm 200 ± 4 μm VIS-NIR, UV-VIS, SR 8 cm 4 cm 230 ± 12 μm XSR 4 cm 2 cm 300 ± 6 μm SR 12 cm 6 cm 400 ± 8 μm VIS-NIR, UV-VIS, SR 16 cm 8 cm 455 ± 22 μm XSR 8 cm 4 cm 500 ± 10 µm VIS-NIR, UV-VIS 20 cm 10 cm 600 ± 10 μm VIS-NIR, UV-VIS, SR 24 cm 12 cm 600 ± 30 μm XSR 24 cm 12 cm 1000 ± 3 µm VIS-NIR 30 cm 15 cm 1000 ± 20 µm UV-VIS 30 cm 15 cm Rule #4: Avoid Excessive Heat
Avoid exceeding the temperature thresholds for the fiber materials: For standard fibers, the temperature threshold for the silica fiber is 300 °C, while the epoxy and PVDF zip tube are rated to 100 °C. For premium-grade fibers, the entire assembly is rated to 220 °C. Jacketing options including stainless BX offer better protection, but it’s always best to consult your Ocean Optics representative for assistance with applications in challenging environments.As one university professor recently shared with us, some Ocean Optics optical fibers in his freshman chemistry lab had “survived” 20 years in the hands of beginning chemists. These fibers might have lasted longer, but a few students got those fibers too close to the flame of the Bunsen burner they were measuring, melting the fiber boot collar and PVDF zip tube.
Chemical resistance is another criteria that may be important for your application. Avoid immersing the fiber in materials that can damage quartz, nickel, steel, aluminum, or the epoxy. In harsh sample environments, choosing durable jacketing materials including silicone monocoil or stainless steel BX is your best bet. Custom sleeves and ferrules are another option.
Rule #5: Remember the Little Stuff
Although this might not always be practical, it’s helpful to replace the end caps on optical fiber connectors when the fibers aren’t in use. This helps to prevent scratches and avoid contamination from dust and fingerprints. Also, we suggest cleaning the fiber ends periodically with lens paper and distilled water, alcohol, or acetone. Avoid scratching the surface. -
How to Ensure Reliable Absorbance Results
Absorbance Repeatability with the Square One Cuvette Holder
IMPORTANT: PLEASE REFRESH YOUR BROWSER IF YOU DO NOT SEE ANY IMAGES/SCREENSHOTS/SPECTRA ON THE PAGE.
Cuvette-based absorbance measurements are only as good as the system used for the measurements. Baseline drift and other spectral changes attributed to varying ambient conditions can be addressed by taking frequent background and reference measurements. Cuvette-to-cuvette variability is overcome using matched cuvettes.
(more…)