AN INTEGRATING RECORDER FOR PHOTOSYNTHETICALLY ACTIVE RADIANT ENERGY WITH IMPROVED RESOLUTION

A device counting fixed amount of parcels of radiant energy efficient in photosynthesis (wavelength region 400 to 720 mμ and recording their total as a digital reading on a counter is described. Radiant energy is transformed by means of a phototube to electrical current which becomes divided into individual parcels by cycles of charging .and discharge of a condenser between two fixed values of potential, and the number of these cycles is counted. From instruments of similar design published earlier the one presented here is distinguished mainly (1) by improved linearity of response in the integrating circuit down to slow counting rates and (2) by the design of a nonselective detector (in the limited range of wavelengths indicated) based on a vacuum emission phototube, which may be combined with the simple integrating circuit used. Thus totals of irradiance (throughout the range of intensities of solar radiation) may be obtained directly in units of energy or in the number of quanta. A very reliable and stable receiver with energy proportional response in the region of wavelength 400–720 mμ (with possible extension up to 1,000 mμ ) was realized using a vacuum emission photocell with photosensitive surface of the double-peak emission type (covering the range from near UV to near IR) and precisely counterbalancing its spectral sensitivity curve by selective absorption glass filters. The RENTSCHLER's type integrating circuit with a cold cathode discharge tube was improved by increasing the maximum counting rate on one side (damping germanium diodes across the coils of relay and counter) and by minimization of leakage in parallel to spare condenser (the contact which shortcircuits the condenser simultaneously with ignition of the discharge tube).