PTB News 1/2007 (432 kB) PTB News 1/2007, English edition, Issue April 2007A worldwide unique goniophotometer with three long-armed robots has now been put into operation. With its newly developed photometer heads, it can detect simultaneously and in a spectrally integrating way photometric, radiometric and colorimetric quantities and at the same time relative spectral distributions by means of a CCD array spectrometer.
It is the task of PTB to distribute the “lumen” unit of the luminous flux, which is fundamentally derived from the SI base unit “candela” for the luminous intensity, on to industry. So far, for calibrations of the transfer standards used for this purpose, a goniophotometer in a fully gimballed suspension construction was developed in the 1970s and used at PTB. Metrological limitations and an outdated computer technology were the reason for a redesign, with which one also expected a reduction in the measurement uncertainties.
The goniophotometer of completely novel design – whose concept is protected by an international patent – was developed at PTB and has now been put into operation. It is composed of three robots, each having 7 controlled axes for moving the slim arms having a length of more than 6.40 m. One robot carries the light source in a freely selectable burning position, aligns it in the instrument center and holds it in position during the measurement. The other two robots each align a photometer head with the light source and divide the room into hemispheres. They can move on any paths at distances of 1 m to 3 m and with measurement periods of typically 10 min to 1 h. The orientation of the robots in the room as well as their kinematic characterisation is determined by means of a laser tracker system. This results in path deviations of the photometer head of < 0.6 mm, and on average only 0.2 mm. The movable photometer heads and a monitor-photometer head are each designed as a tristimulus colorimeter head with 4 channels. In addition, they contain an unfiltered Si-photodiode for radiometric measurements and a CCD array spectrometer. Thus, light, colour and optical radiation are measured through the same light-entry window, all photo currents are measured in parallel and converted to frequencies. This allows the simultaneous measurement of all 18 channels with synchronous triggering and any integration times whatsoever, optimally adapted to the motion sequences of the robots and the modulations of the light.
With the new robot goniophotometers, it is now possible to determine, in addition to the photometric, also chromaticity data of light sources at considerably reduced measurement periods. By using the freely programmable robots, nearly any measuring head paths and near- and farfield measurements whatsoever are possible. The ozone-proof version of the goniometer also allows, in addition, the measurement of UV lamps, and due to the adjustable temperature range of 25 °C to 35 °C, luminescent lamps can also be measured at the respective luminaire temperature.