BTS2048-UV-S-WP

BTS2048-UV-S-WP BiTec sensor spectroradiometer for high-quality outdoor UV measurements

The BTS2048-UV-S-WP is a high-quality spectroradiometer whose compact design and elaborate optical, electronic and mechanical interfaces make it ideal for high precision outdoor UV measurements. Due to its innovative filter and spectrometer design it is able to measure solar radiation with a very good straylight reduction performance. Accordingly, even the edge of the sun below 300 nm can be resolved for some orders of magnitude (see figure 2). With the included S-BTS2048 application software, precise measurements and data analysis (Erythema, ICNRIP, etc.) can be performed intuitively. In addition, the spectral range can be extended from the UV to the NIR with the complementary BTS2048-VL-TEC-WP. Applications in the whole Si spectral region (e.g. solar-cells) are possible.

BiTec sensor for high-end light measurement 

One of the outstanding features of this exceptional spectroradiometer is its BiTec sensor (see technical article about BiTec sensor). It combines the special properties of a photodiode with those of a back-thinned CCD diode array. Through bilateral correction of measurement signals from both sensors, the BiTec sensor ensures precise radiometric and spectral-radiometric measurement values over a large dynamic range.

Spectrometer based on a high-quality back-thinned CCD detector 

The spectrometer unit is based on a CCD with usable spectral responsivity range between 190 nm and 430 nm. It has a 0.7 nm optical bandwidth and a pixel resolution of 0.13 nm/pixel. Due to the back-thinned technology, the CCD is substantially more sensitive as compared to conventional front-illuminated CCD chips. Furthermore, the CCD is one stage cooled (1TEC) to reduce the dark current and and thereby increase the signal to noise ratio.

Precise spectral radiometry (low straylight)

To facilitate optimal use of the CCD sensor‘s dynamic range and to overcome the problems of most array spectoradiometers in the UV range, a remote-controlled filter wheel (open, closed, optical filters) is located in the optical beam path. This filters combined with smart measurement and stray light correction routines enables high quality measurements of the BTS2048-UV-S. Results are comparable with double monochromator results (see figure). However, the measurement duration is significantly lower.

The BTS2048-UV-S-WP is equipped with a particular set of filters optimized for solar irradiance measurements. Those allow a superior stray light suppression compared to other spectroradiometers that puts the device’s performance on the same level as double monochomators. The results of a direct intercomparison study are presented here.

However, the BTS2048-UV-S-WP cannot only be used for solar irradiance measurements but for the measurement of other UV sources as well. Usually, no WP (weather proof version) is required for that particular purpose (see the models BTS2048-UV and BTS2048-UV-S). In some applications e.g. when measuring extraterrestrial solar simulators, a good stray light suppression is key to precise measuring results. Gigahertz-Optik’s stray light calibration technique can be used in combination with further smart measurement routines to enable the superior stray light suppression. See also our technical article about stray light reduction for spectroradiometers. The calibration of a BTS2048-UV-S-WP’s additional stray light correction matrix is available optionally on request.

WP means weather proofed

The housing of the BTS2048-UV-S-WP is designed for outdoor measurements. The cooled back-thinned CCD and the spectrometer unit are temperature controlled in a second housing. In this housing, humidity is removed by an exchangeable cartridge. In order to avoid deposits of dust, rain or snow on the entrance optics on the entrance optics the quartz dome is blow-dried by warm air.

Diffuser window directly connected instead of light guide 

As for the input optics, the BTS2048-UV-S-WP has an incorporated diffuser window with a cosine corrected field of view. The fact that a light guide has not been used improves sensitivity and calibration stability which is a big advantage for outdoor use. The device‘s compact size is also of significant benefit. The f2 error of the cosine corrected field of view to less than 3% makes it possible to use the BTS2048-UV-S-WP for direct measurement in absolute radiometric quantities:

● Irradiance (W/m²)

● Spectral irradiance (W/(m² nm))

State of the art interface

The BTS2048-UV-S-WP is controlled via a USB 2.0 or Ethernet interface. With regards to the communication speed and cable length, the Ethernet port is superior to the USB2.0 interface. Furthermore, data preparation occurs in the BTS2048-UV-S-WP to optimize the data-transfer speed. For this purpose, an independent, high-performance microprocessor is incorporated. Data and power interface are of course of weather-proof design as well.

User software with flexible desktop structure 

The BTS2048-UV-S-WP‘s scope of delivery includes the S-BTS2048 user software. One of the characteristic features it has to offer is the flexible desktop that can be individually configured by the user.

This entails a potpourri of graphical and numerical display windows from which the user can choose:

● Freely definable numerical displays in decimal or scientific representation. Zoom function.

● Numerical display fields for radiometric, spectral and other measurands.

● Measurement protocol of the selected measurement parameters.

● Spectrum. Zoom function.

● Data logger. Zoom function.

Traceable calibration 

Calibration of the BTS2048-UV-S-WP, including its accessories, is performed by Gigahertz-Optik ISO/IEC 17025 calibration laboratory for optical measurands with reference to national and international calibration standards. Due to the small dimensions of the device it can be shipped easily for re-calibration purposes.

International Measurement Campaign

Additional to the above mentioned scientific campaign the BTS2048-UV-S-WP has took part in an international intercomparision (ATMOZ) in Tenerifa, to prove the quality of the measurement data in the scientific framework in TOC measurements.

A scientific publication by INTA showed a very good agreement in a three comparison campaigns of global UV spectral irradiance measurements: Comparison of global UV spectral irradiance measurements between a BTS CCD-array and a Brewer spectroradiometer.