Spectrometer, Filter, Wedge
Wednesday, September 20, 2006
The Filter Wedge Spectrometer has been designed and developed with a rotating interference Filter Wedge wheel in the shape of an annulus split along a diagonal. One semicircular half continuously covers 1.2 to 2.4 microns wavelength, and the other half covers 3.2 to 6.4 microns wavelength. The Spectrometer used a lead selenide photodetector, which is cooled by thermal radiation to 165 K. The field of view is 2.6° with a resolving power (λ/δλ) of 100. The weight of the Spectrometer is 13 pounds and a power load of 9 Watts.
Photodetector are used to detect the start of a scan, 90° and 180° rotation of the Filter Wedge wheel. This Filter wheel position data is used to control the calibration circuit. The calibration circuit counts the number of Filter wheel scans and commands the Spectrometer into a calibration cycle after 47 scans.
During the calibration cycle, the preamplifier input is switched from the photodetector to the output of the calibration circuit. Four step voltages modulated at the 300 Hz chopper frequency and in phase with the chopper reference voltage are gated into the preamplifier during the first quarter cycle. Four step voltages chopped at the 300 Hz rate and out of phase with the chopper reference voltage are gated into the preamplifier during the next quarter cycle. During the last half cycle, a signal causes a calibration target to cover the optical port is generated and preamplifier input is switched back to the photodetector output. The calibration target temperature is at least 10 K cooler than the reference target and is presented during the 3.2 to 6.4 micron wavelength filter scan.
Source: “Meteorological infrared instruments for satellites” by I. L. Goldberg, NASA Goddard Space Flight Center, SPIE Proceedings, Volume 1 (1969), 13th Annual Technical Symposium
Reference: None Available
Industrial Products
posted by JD52 @ 8:30 PM,
