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APPN:NUIX C <br />NSA Record Triggering Device <br />As part of this project, NSA built a nonintrusive, intrinsically safe device to trigger <br />recording of seismic signals when firing shots in the injection well (figure Cl ). <br />"I'he device was designed to detect changes (an impulse) in the magnetic Held around the <br />firing line when the line was UL powered to lire a shot. Each detected impulse was <br />sufficient to trigger digital recording of seismic waves by the seismograph. This impulse <br />was recorded on a selected seismograph channel (channel #1). <br />The actual discharge that t~~llowed was initiated by the blasting operator by manually <br />increasing voltage/current levels in the firing line. Auer an initial experiment on the first <br />day of the survey, the delay between triggering the seismograph and an actual shot was <br />reduced to less than 1.5 seconds. The train of reflected seismic waves within 0.5-second- <br />long tirnc window could be thus recorded within two-second-long records. This time <br />window was sufficient to adeyuatcly cover possible reflective anomalies (solution <br />caverns) within the surveyed site. <br />NSA security swdch box <br />Push to stand-by for 2 <br />firing ••S 3 <br />t <br />e <br />Weatherford security installation! finng line <br /> <br />-100 VDC out Weatherford blaster <br />Common ground <br />~ To NSA <br />- seismograph <br />Common ground <br />Figure L' 1 Block schematic of NSA nonintrusive, intrinsically safe triggering device. <br />