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NSA APPENDIX C <br />NSA Record Triggering Device <br />As part of this project, NSA built a nonintrusive, intrinsically safe device to <br />trigger recording of seismic signals when firing shots in the injection well <br />(figure C1). <br />The device was designed to detect changes (an impulse) In the magnetic <br />field around the firing line when the Ilne was DC powered to fire a shot. <br />Each detected impulse was sufficient to trigger digital recording of seismic <br />waves by the seismograph, This impulse wos recorded on o selected <br />seismograph channel (channel #1). <br />The actual discharge that followed was initiated by the blasting operator <br />by manually Increasing voltage/current levels in the firing line. Alter an <br />Initial experiment on the first day of the survey. The delay between <br />triggering The seismograph and an actual shot was reduced to less than <br />1.5 seconds. The train of reflected seismic waves within 0.5-second- tong <br />time window could be thus recorded within Iv/o-second-long records. This <br />time window wos sufficient to adequately cover possible reflective <br />anomalies (solution caverns) within the surveyed site. <br />N$A .xumy.wnm Dow werr~enon, rnmb natr.pp,~ ~ nwq uro <br />a,an a rw.oa ra ~ ~. <br />nnrq u <br />e <br />N5A Vlppv ~ <br />51x/0 <br />I ~ <br />.. ~ .. ~ To N$.~ <br />~~ <br />Ci.~~~m~i Jro~mO <br />-700 VDGW <br />WM1inb0 Oda10N <br />I <br />~ ,~ <br />~~ <br />Figure C1 -Block schematic of NSA nonintrusive, Intrinsically safe <br />triggering device. <br />