sdqel tb vi BLS EVALUATION OF INSTRUMENTS 3.10 3.10.1 Rain Gage The land-based rain gages operated successfully where they were not damagedbyblast. The biggest difficulty experienced with the rain gage was that the inking system was not designed for writing on a floating support even when provision had been made to dampthe action created by wave motion by the use of a gimbal. The lagoon was much choppier than San Francisco Bay, where the instrument was initially tested, and as a consequencethe ink in the pen was rapidly used up in drawing a very broad high-frequency trace. This necessitated changing to an improvised smoked chart on which the dry pen acted as a stylus, The tracings were sprayed with Krylon when they were recovered, to prevent smearing. Thisimprovisation did not eliminate the broadness of the trace caused by the action of the waves. Therefore, although large changes of rainfall were readily apparent,Amal increases that may have occurred dur- ing the fall-out were not. + Bids mart The shields for the rain gages as employed on the lagoon stations.were very effective. None of the lagoon-based rain gages suffered damage, and only the closest received thermal burns on the unshielded top surface area. The land-based rain gages which were not shielded, on Alice and Janet, were damaged severely by blast. oe When rain gages are used afloat, the following items should be checked to assure the most satisfactory results: polyethylene or some such inactive plastic bucket should be used if the fall-out is to be recovered; the tracing device should be modified so that it is less sensitive to motion and more positive in its action; a circular type gimbal mount for the rain gage would provide better stability; and the shielding of the rain gages by a steel tube should be accom- plished on all close-in stations. The use of rain gages ashore presented no great problem, and the type used was satisfactory where information accurate to +0.05 in. is sufficient. 3.10.2 Incremental Collector Rete a This instrument was designegas € liqG#fcollector and, since thé fall-out was composed of particulate matter, no valid conclusions. as to its effectiveness could be drawn. 3.10.3 Differential Fall-out Collecté#-~ The basic design employed in this collector had many valuable features. Moving the aperture rather than the colled#fing trays eliminated the need of a large power source. The problem of cross contamination of collecting trays was minimized by the close fit between the moving belt and the tray and the fact that, once sealed after collection, the trays were not opened until analysis was begun at the laboratory. Furthermore its relatively light weight, approximately 60 lb exclusive of ita externai,power source, made it easy to handle by one man. The increment rate could be yaried by changing gears, and such change allowed for a variation in total collecting time, whichwas highly desirable,» Besides a failure of trigger mechanisms, |the following problems were encountered in the operation of this instrument: = 1, The moving belt jammedby sticking in its guides and was torn. 2. In one case the belt-stopping microswitch failed to stop the belt at the proper instant, thereby exposing the tray to the elements. 3. Two of the 6-volt storage batteries shorted out on the lagoon stations. 3.10.4 Trigger Mechanism The bomb-light-sensitive triggers functioned very well. There was one failure on the lagoon stations due to a faulty relay; the land~station triggers operated sporadically and unsuccessfully. The reason for their failure is not known. Probably they experienced sometypeof thermal shielding. 31