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500A: 16 Channel Microseismic Data Logger

The 500A Microseismic Data Logger (MDL) system provides real-time monitoring of microseismic events within a mine. Low-noise signals are ensured by the use of a preamplifier and balanced line driver circuit in each transmitter. Sensors can be located up to 3 kilometers from the MDL (distance can be extended to 7 km if repeaters are installed).

The Microseismic Data Logger  is normally located within the mine at a central location where power is available. A transmitter is located close to each of the sensors to be monitored and wires (2 twisted pair cable) connect each transmitter to the MDL. No power is required at the sensor since the transmitter is powered by the MDL.  Systems are available for monitoring either 8 or 16 channels of data. Any channel can be connected to a passive geophone, a closure meter, a 4-20 mA sensor such as a pressure transducer or to a voltage output sensor.

The Microseismic Data Logger contains a PC-type computer, a data acquisition card, one or two 8-channel receivers, power supplies and a thermoelectric cooler. Terminal block connections on the front panel of the MDL allow easy connection of the sensor cables from the transmitters. Connections are also provided on the bottom panel for input power, Ethernet, video monitor, keyboard, mouse and a USB port. Power to each transmitter can be controlled using switches on the MDL front panel. LED indicators are provided to show the power status of each transmitter.

Software

The Microseismic Data Logger operates using a real-time version of the LINUX operating system. MISER (MIcroSeismic Event Logger) software written by Kosteniuk Consulting Ltd. logs all detected events. Event triggers for each channel can be set to either threshold or STA/LTA type. Once an event has been detected MISER logs it to hard disk in SEG-Y format. MISER also handles communication with other computers. A remote computer can request event data from the MDL, perform data file management, set up the data logger and view the status of all recorded events. MISER works in conjunction with the CANSEIS software also written by Kosteniuk Consulting Ltd. CANSEIS is a signal processing program specifically designed for the analysis of microseismic data that processes event data and calculates source location, event energy, moments, slip times, and also places error bounds on the source coordinates. Processed data is output in ASCII format which allows the data to be easily read by other software packages. CANSEIS can display the source location and magnitude of events on a 2D mine site layout.

  • 500B: 8-channel Microseismic Data Logger
  • 500C: 4-channel Ethernet Microseismic Data Logger
  • monitors passive geophones, pressure transducers and closure meters
  • preamplifier and balanced line driver located with sensor
  • sensors can be located up to 3 km from the data logger (repeaters are available to extend distance to 7 km)
  • 16-bit A/D converter running at 1000 Hz per channel, auto ranging A/D at gains 1 and 10
  • systems with 8 or 16 input channels
  • uses standard PC and A/D hardware
  • data logger and transmitters NEMA 3S rated (protected from dust and splashed water)
  • low cost
  • complete systems, including transmitters, data logger, and software

500A – Microseismic Event Detection

CHALLENGE

In 1999 Dr. Prugger from Potash Corporation of Saskatchewan (PCS) wanted a simple, low-cost and low noise solution for monitoring microseismic events within a potash mine.  He had done work on using microseismic event magnitude and source location data to predict the long term health of large, soft rock underground mines.  All of the commercially available microseismic data recording systems had been designed for mobile exploration of minerals, but not for long-term continuous monitoring within a mine.  Other than high cost, another issue with these commercially available systems was that the signal quality was adversely affected by the presence of the high voltage, high current power wires that ran throughout the mine.  For this work he required a robust, low-cost data logger that was immune to 60 Hz power line noise which could be situated at a convenient location within the mine and be connected to an array of geophone sensors.

SOLUTION

Aurora Scientific’s R&D team had significant experience developing custom products from off-the-shelf computer data acquisition systems.  In order to meet the low-cost specification we used a desktop PC with a plug-in data acquisition card mounted in a rugged industrial enclosure.  To address the noise issue on the signals we developed a low-noise pre-amplifier with a balanced line driver that would be co-located with each geophone.  In order to perform source location of microseismic events the data logger needed to be able to maintain timing accuracy to 10 microseconds.  The use of a real-time Linux kernel as the operating system of the PC ensured this very high level of timing accuracy.

RESULTS

A 500A Microseismic Data Logger (MDL) was built and delivered to PCS along with custom computer programs developed by our subcontractor Kosteniuk Consulting.   The new MDL provided PCS with microseismic event detection and recording.  A second program provided by Kosteniuk Consulting was used to download the event data from the MDL and perform source location.  The use of a pre-amplifier and line driver located with the geophone reduced the noise on the geophone signal by two orders of magnitude.  This allowed simplified event detection to run in real time on the MDL and eliminated the manual digital filtering of signals that was required with the previous solution.  The product proved to be so useful that PCS purchased systems for most of their mines and other potash producers in Saskatchewan also adopted the Aurora Scientific MDL as their microseismic monitoring system.

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