In blasting and seismic measurement operations, detonators and explosives are buried in the ground, for example, in holes (often referred to as “bore holes”) drilled into rock formations, etc., and the detonators are wired for external access to blasting machines that provide electrical signaling to initiate detonation of explosives. A tremendous amount of pressure is developed in the boreholes during blasting, and excessive pressure from the firing of one detonator may impair detonators, whether non-electric, electric, or electronic. This situation can be particularly problematic where a plurality of detonators are in a single borehole, and an earlier-firing detonator can produce a pressure wave that disables a later firing detonator in the same borehole. Dynamic pressures during blasting, especially sympathetic pressures from adjacent holes or underlying decks, have been suspected to cause misfires in electronic and non-electronic detonators. Measuring borehole pressures during detonation can facilitate understanding the magnitude of the pressure developed as a function of blasting conditions on the resulting fragmentation, and will help advance the blasting technology. Further, steps may be taken to alleviate such excess pressures based on borehole pressure measurements.
Thusfar, borehole pressure measurement is primarily done using carbon resistor sensors and strain gauges, which exhibit changes in electrical resistance upon external pressure conditions. However, carbon resistors and strain gauges are piezo-resistive i.e. the resistance changes with external pressure. These sensors, moreover, typically require elaborate mounting and must be supplied with a constant current or a voltage divider as well as thermal compensation and autozeroing via a bridge circuit for proper electrical biasing and feedback. Moreover, conventional borehole pressure measurement techniques are generally costly and complex. Manganin foil gauges have been used for high detonation pressures, and are attractive because of their extremely low thermal coefficient of resistivity and high sensitivity towards hydrostatic pressure. Conventional piezoelectric pressure sensors tend to be expensive and bulky, and often require bulky extraneous charge amplifiers and noise filtering electronics to acquire the signals. Thus, a need remains for improved techniques and apparatus for measuring borehole pressure during blasting operations.
USPTO Backgrounds
USPTO Backgrounds