A thermopile radiometer was built as part of an ARC Interactive Heating Facility (arc jet) characterization campaign. The thermopile sensor signals were amplified by custom made electronic circuit boards for compatibility with the IHF facility data acquisition system. The two outputs of the sensor (exposed measurement element and shielded temperature compensation element) were conditioned by a two-channel instrumentation amplifier.
Two versions of this amplifier were built – one with a gain of ~60 for direct measurement of plasma with an anticipated mV input range, and another with a gain of ~6000 as a calibration unit for use with a comparatively dim calibration source with an anticipated μV input range. Both amplifiers were further conditioned by a 2-pole active low-pass filter with a 250 Hz cutoff. Characterization of the circuits was performed with a precision μV/mV voltage standard to determine offset voltages and gain accuracy.
The instrument successfully measured heat fluxes in the IHF facility as part of a larger campaign with multiple instruments. The results were published at the 42nd AIAA Fluid Dynamics Conference, New Orleans, Louisiana, June 25-28th, 2012 in the following paper: M. Winter, G. Raiche, I. Terrazas-Salinas, F. Hui, B. White, Measurements of Radiation Heat Flux to a Probe Surface in the NASA Ames IHF Arc Jet Facility. The full text of the paper can be read here: http://explore.mohodisco.com/radiometer.pdf.
This instrument could be easily adapted for use in spaceflight as a total radiometer package or even as a receiver for a simple laser range finder.