Laserfiche WebLink
NSA APPENDIX C <br />NS:~ Record Triggerini; 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 C 1). <br />The device was designed to detect changes (an impulse) in the magnetic <br />field around the firing line when the line 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 was recorded on a 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. Affer 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- long <br />time window could be thus recorded within two-second-long records, This <br />time window was sufficient to adequately cover possible reflective <br />anomalies (solution caverns) within the surveyed site, <br />NSA secunty switch box Weatherford secunty instanabon ~ nnng une <br />Push to stand-by for <br />fm rn1 <br />~ To NSA <br />seismograph <br />mon ground <br />100 VDC out Weatherford blaster <br />Common ground <br />Figure Cl -Block schematic of NSA nonintrusive, intrinsically safe <br />triggering device. <br />