Spectral Measurement Applications

Jeti GmbH, located in Jena, Germany, develops and produces spectroscopic equipment. Given the numerous benefits offered by USB devices, Jeti had decided to implement USB interfaces on their spectral measurement devices - specbos 1000 (spectrometer) and specbos 1100 (spectroradiometer). Using a Mitsubishi microprocessor, the Philips PDUSBD12 USB interface for communication over USB, and data acquisition software development tools from National Instruments - Lab Windows CVI, Jeti set out to create a USB spectrometer*(specbos 1000) and a USB spectroradiometer**(specbos 1100).

Jeti's spectrometers, specbos 1000, 2000, 3000 are used by vendors of various types of "illumination" devices such as television sets, car-displays, LCD displays, LED displays, traffic lights, lamps, that have to comply with certain standards, for example color, brightness and spectral dissipation. Jeti's spectroradiometer, specbos 1100, measures diffuse light sources, screens and other such devices.

Prior to implementing the USB standard, Jeti's spectrometers were based on the RS232 serial port communications standard. The motivation for implementing a USB interface were achieving true plug and play capabilities, fast and secure data transmission, and simple cabling. Having taken on the task of implementing USB, Jeti's engineers were unaware of the daunting task that lay ahead of them in the form of developing their applications and USB hardware access.

A General Description of the Products
Please refer to the block diagram below. The specbos 1000 (spectrometer) and specbos 1100 (spectroradiometer) operate as follows: Light from an application specific measurement head is guided through fiber to the spectrograph. The spectrograph is made up of the fiber-input, the grating and the photodiode-array. The grating diffracts the light into the different parts of the spectrum. The diffracted light is then imaged on to the photodiode-array. The photodiode-array's video signal shows the spectral distribution of the light in pixel format. This analog information is converted into digital values with a 16-bit analog to digital converter (ADC). The values from this converter are read by the micro-controller and calculations are performed (for example, pixel-wavelength relationships), so the spectra can be transferred to an application program that resides on a PC. In this application, further calculations can be done to determine color coordinates, radiation data of light sources (luminance, illuminance), width of film and many other properties, depending on the application.