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| Sensors |
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1. Bill Yee at PJV’s Dome Mine asked which GMM would be best for monitoring cracks in a pit wall? The SPECTRE GMM is very well suited to monitoring of cracks in a pit wall because the probe is flexible and can therefore follow any component of shear that may occur.
Other advantages offered by the SPECTRE GMM are:
2. Jairo Gomez at Mosaic’s K2 mine has arrays 3-4 DETECT GMM’s to construct multipoint extensometers. He asked us to provide some guidelines for the interpretation of his data and the result is a borehole extensometer application note which applies to all YieldPoint multipoint extensometers. The note is available here:
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| DESTINY/IP |
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| Dataloggers |
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1. How the 9V batteries are housed in the SLUG4 datalogger? The foam in between allows the batteries to snap into the lid. 2. A very common question is: "Is it worth me using a SLUG data-logger or should I just take regular manual reading?" The figure shown below is an example from one of our customers who attached the sensor to a basement floor spanning a crack. Readings were taken hourly using a SLUG datalogger.
The plot is data collected over a 3 week period in the spring of 2007 from two sensors. The light blue plot is temperature, and the diurnal temperature cycles (right hand scale) are obviously visible, especially on sunny days. The Blue tip sensor (SPECTRE GMM) has a resolution of 0.01mm and the microSPECT 0.001mm. First thing to note is that the movement are very small (0.050mm or 0.002”). The microspect output follows the daily temperature cycle and in particular the trend of crack closure (-ve value) with higher temperature. The solid lines for each sensor are the 1 day moving average and they will relate to the longer term variations of temperature. The main point here is that collecting data every hour builds confidence in the data and allows moving averages to remove daily fluctuations that may occur. Another example is shown below. Temperature and humidity were monitored deep U/G at Creighton mine. The effect of the ventilation system cycles can clearly be seen on Temperature (red) and humidity (blue).
3. John Babcock from Sauls Seismic asked: “How many samples should the SLUG data logger hold?” The Datalogger has 512kbits of memory. Each record takes 104bits (13 bytes) therefore the SLUG can hold 4900 readings or about 200days worth at 24 readings/day. However, it is the battery-life that is the limitation and if you want to maximize battery life use a 9V lithium (approx 1200mAh capacity compared with 650mAh for an alkaline). You can source these out using the internet. Panasonic makes one which you can buy through digikey (www.digikey.com) $10each but it can be worth it. The SLUG draws 0.07mA (70uA) when it is sleeping between readings so without taking reading it will has capacityfor 650/0.07=9285hrs or more than 1 year. However it draws aprox. 20-30mA when taking a reading over a 45sec period. This is equivalent to an average draw of 20mA * 45/3600=0.25mAh averaged over an hour. So average draw of 0.25mAh for the reading + 0.07mAh to sleep= 0.32mAh. So for an alkaline battery the capacity is 650mAh and theoretically the life should be 85(650/(0.32*24)) days. We recommend changing the battery after 30-40 days based on our testing. A lithium should be good for 60days +.
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