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<br />HARDWARE <br />The basic hardware for controlling the dispensers includes: <br />1) datalogger/controller (Campbell Scientific Inc. (CSI) CR10); 2) <br />transceiver (Motorola P50); 3) radio modem (CSI No. RF95) 4) foul-weather <br />antenna (Sinclair No. SRL-2010C)1 and 5) 4-channel relay (CSI No. A21REL-12). <br />The liquid propane dispenser includes: skinner valve (Honeywell No. <br />VSRBMS8440), flowmeter (FloScan No. 2018-18 and 3005), filter, nozzle (LHN3 <br />brass), termocouple (CSI lOST) and tubing. The tubing from the tank to the <br />nozzle is insulated to keep the liquid propane from vaporizing. The <br />controller and dispenser unit described above is identical to the one tested <br />during the winter 1993. <br /> <br />The base unit (Freds Flat) has the above features plus is equipped to: <br />1) measure wind direction with a heated Hydrotech vane (WO-3); 2) measure wind <br />speed with a heated Hydrotech anemometer(WO-3)1 3) measure air temperature and <br />relative humidity (CSI No. HUP35C-U) mounted in a Hydrotech foul-weather <br />radiation shield (AT-2); and 4) measure the presence of supercooled liquid <br />water (SLW) with a tower-type icing detector (Rosemount 872812). Figure 2 is a <br />schematic of the base unit. The basic costs (exclusive of the liquid propane) <br />for both a base unit and a satellite unit are shown in Table 2. <br /> <br />TRIGGERING ALGORITHM <br />The datalogger at Freds Flat is programmed to calculate 1-hour means of wind <br />direction, wind speed and air temperature. The datalogger also monitors the <br />number of deicing cycles ("trips") from the Rosemount icing rate meter over <br />the past 2 hours. The 1-hour means and summation of trips per 2 hours are <br />recalculated (updated) every 12 minutes. Cloud seeding commences from all <br />three dispensers whenever the following conditions have been met by the I-hour <br />means and 2-hour summation of trips. <br /> <br />7 <br />