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ABSTRACT: This paper describes the use of a modified piezoelectric sensor and the supporting electronics which were used to measure instantaneous borehole pressures from adjacent boreholes during blasting. The key features of this measurement approach are the relatively low cost and ease of set-up in the field rather than bulky electronics on-site or complicated pre-calibration procedures. SPICE (Simulation Program Integrated Circuits Emphasis) was used to simulate the time-dependent outputs from the circuitries. The system was compared with respect to a commercial pressure sensor inside a water tank where an underwater testing of standard output electronic detonators were utilized; excellent agreements between the measurements of both systems were obtained at 34-128 MPa range. The actual outputs also compared well with the SPICE simulation results. Results are presented on several blasts where non-electric and electronic detonators were used. Single primed and decked shots were monitored; in dry holes, sympathetic pressures from neighboring boreholes or underlying decks of 34-48 MPa were measured while wet holes can exhibit almost 69 MPa of peak pressure. This system can measure a maximum pressure of 138 MPa in the boreholes.
1INTRODUCTION
1.1 Borehole pressure
Boreholes can develop tremendous amount of pressures during blasting. Excessive pressures can impair detonators, especially electronic detonators. Electronic detonators are increasingly being adopted in the last few years in a variety of applications. Electronic detonators offer several distinctive features over electric and non-electric detonators, including safety, traceability, field programming of delays, better timing accuracy resulting in improved fragmentation, reduced vibration and noise control. 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 the pressures during blasting can aid to understand the magnitude of the pressure developed as a function of blasting conditions on the resulting fragmentation.
1.2 Conventional measurement techniques
Classical methods to measure pressure consist of carbon resistors(Austin et al. 1991a, 1991b & 1995), strain gauges (Hoffmann. 2002) or piezoelectric sensors (Grinenko et al. 2004, Huni et al. 1970 and Wang et al. 2010). Carbon resistors and strain gauges are piezo-resistive i.e. the resistance changes with external pressure and they usually require elaborate mounting, constant current source, the proper voltage divider, thermal compensation and auto-zeroing via a bridge circuit. Manganin...