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Search result for: id10=WA 0821 7001 0763 (FORTRESS) Ukuran 2 Pintu Rumah Air Manjunto Mukomuko
| # | Post Title | Result Info | Date | User | Forum |
| What is an “air wave”? | 13 Relevance | 2 years ago | Gretchen Schmauder | General Seismograph Info | |
| An Air wave is simply the sound or acoustic wave created by the source, which by definition is what travels through the Air rather than the ground. It is what you hear. In most cases, the seismic velocity of the near surface materials has higher than the velocity of sound in Air. But in some cases the Air wave is faster, and can arrive at the geophones before the seismic first break. This can make the first breaks difficult to pick. An example of an Air wave is shown below. The traveltime graph of an Airwave is linear, and will be about 330m/s. It is generally lower in amplitude and higher in frequency than the first break, and can generally be dealt with in processing using a low-cut filter. | |||||
| Good Practice - Charging the Atom | 4 Relevance | 2 years ago | Gretchen Schmauder | Hardware | |
| Attachment : Bulletin_Good Practice-Charging the Atom.V1.pdf This bulletin is written to inform those customers who purchased the ATOM 1C and 3C seismographs (“Atoms”), to allow for out gassing and temperature cooling when charging the batteries. Background: Geometrics has noted that some users use fitted cases for their Atoms to allow for safe shipping and handling between deployments. If the Atoms are fitted with charging cables and are being charged while inside the fitted cases, under certain circumstances, the fitted cases may not allow for sufficient Air circulation and could lead to excessive temperatures inside the Atom unit. These excessive temperatures can exceed the battery manufacturers suggested safe charging temperature, resulting in some instances in out-gassing of hydrogen during the charging process. Recommendation: Geometrics recommends that users remove their Atom unit(s) from any enclosed/insulated boxes (including fitted cases) prior to charging. Each Atom unit requires adequate surface to Air access for heat dissipation. We also recommend that users do not leave the Atom unit on charge for long periods of time. Geometrics recommends that a typical maximum charge time should not exceed 12-15 hours. Precautionary Steps: In addition to using good practice charging as we have described in this Bulletin, Geometrics will provide users a procedure for installing a GORE® Protective Vent to allow for the release of pressure and gas from inside the fitted case housing should such pressure and gas accumulate. These vents can be installed at local service centers or at Geometrics factory. Please contact our Geometrics Support organization at for additional information. | |||||
| Does using a magnetometer pose a health risk? | 4 Relevance | 2 years ago | Gretchen Schmauder | General Magnetometer Info | |
| The cesium used in our magnetometers is the non-radioactive elemental metal, isotope Cs 133. We employ approximately 120 to 240 micrograms of cesium metal in the sensor divided between the lamp and absorption cell. These are small glass ampules, each containing a volume of 1/32 to 1/16 of a cubic millimeter of cesium. If either or both the lamp and cell should break the cesium will instantaneously react with the Air and moisture in the Air to become Cs2O and/or CsOH. Both compounds are caustic but the quantity is so small that it is of no health concern. Finally, the lamp and the cell ampules are contained in a G10 housing that is then contained inside a sealed PVC housing. If the sensor should cease working due to a broken lamp and/or cell, it is not field repairable. Return the sensor to Geometrics for repair, replacement and/or disposal. | |||||
| RE: SD problems | 2 Relevance | 8 months ago | Rui Zhang | Hardware | |
| I assume you can feel the spring when you insert the micro-SD card. Did you try to format your micro-SD to exFAT? The other thing I can think of is somehow there is dirt stuck inside the SD socket. Maybe try to blow the socket with Air. | |||||
| Intermittent Issue Diagnosis | 2 Relevance | 2 years ago | Rui Zhang | Hardware | |
| General information The most common symptoms of intermittent connection issues are shown below: D_CY shows a background decay signal is either much higher than normal, and/or C_CY is a flat line (doesn’t decay). Figure 1 Intermittent connection issue. Where is the failure occurring? The two most common places where intermittent issues occur are at the two ends of the Rx cable: the joint between the Rx cable and the Cart and the joint between the Rx cable and the EDA box (orange box). Now we need to identify which joint has the intermittent issue. Set up the MM2x2 in DAM mode. Collect DAM data while keeping the Cart stationary but tapping one joint. Collect another DAM data while tapping the other joint. Analyze the DAM data by plotting the “Monostatic_5” for all 12 Rx channels in Geosoft. The channels having intermittent issues will appear much noisier. If you have MatLab software, you can download the MatLab code to analyze the DAM data. Example plots are shown below. It is obvious that “ZA” channel has the intermittent issue in Figure 2 and “XB” channel is open in Figure 3 (very flat line, no noise at all). Click here to download the code: Attachment : Intermittent_noise_full.zip . If both DAM and IVS data have the same problematic channel(s), we are confident that the intermittent issues observed in IVS data are repeated in DAM data, and by tapping at that location, we are able to identify the intermittent joint. Figure 2 Intermittent "ZA" channel. Figure 3 Open "XB" channel. What to do next? Disconnect the problematic joint and clean the connectors on both sides thoroughly (using an acid brush and a can of compressed Air). Reconnect and try the tapping method again. If the problem goes away (no more noisy channels), the intermittent issue is likely caused by dust. If cleaning doesn’t fix the problem, swap out the Rx cable and repeat the tapping method. If the problem goes away, it is likely caused by a bad Rx cable. If there is another set of EDA and Cart available, swap out the EDA and the Cart to identify the problematic part. If not, use the tapping location to identify the problematic part. Fill out the RMA form at . If it is the Cart, send in the whole system for inspection/repair. You can contact Geometrics for MM2x2 rental if you need to continue your work during the down time. If it is the EDA, we recommend sending in the EDA only. It will save your repair time since it is much faster to unpack/pack/ship the EDA than the whole system. You can contact Geometrics for EDA rental if you need to continue your work during the down time. Warning Please note that this tapping method should ONLY be tried when intermittent issues have been observed in IVS tests. It is NOT recommended to use it as a daily QC test because it does put extra stress on connectors and likely leads to a shortened connector lifetime if applied too often. | |||||
| Half Rigid Suspension Design | 2 Relevance | 2 years ago | Rui Zhang | Hardware | |
| With the provided 10-feet suspension cables, the magnetic noise due to most commercial drones can be ignored. However, some MagArrow customers experience stability issue, especially in windy conditions. For a small number of drones, the MagArrow can be attached to the landing gear directly with acceptable noises (line-levelling is still required in data processing). For most drones, however, this configuration causes too much noise. A half rigid mounting design may solve this problem. It has 2 rigid bars with hinges on one side and 2 flexible cables on the other. On the ground, the rigid side folds to the side. While in the Air, gravity will keep the MagArrow further away from the drone. Drone noise can be greatly suppressed since the noise follows 1/R^3. A factor of 2 increase in the separation can lead to a factor of 8 decrease in noise. Please make sure the hinges and the rigid bars are made of non-magnetic material. | |||||
| Is it necessary to bury geophones for seismic surveys? | 2 Relevance | 2 years ago | Gretchen Schmauder | Application | |
| This is rarely necessary or helpful, even in high noise conditions. If you are having difficulty with Air waves, burying the geophones might blunt their effect. If planted properly, wind is generally not a factor, and if it is, it is usually via vegetation vibrating around the geophones, which would not be mitigated by burial. | |||||
| What is Seismic Refraction | 2 Relevance | 2 years ago | Gretchen Schmauder | General Seismograph Info | |
| All wave phenomena, the most familiar being visible light, are subject to refraction, or a change in propagation direction, at interfaces between materials of contrasting propagation velocities. The bigger the difference in velocity, the more the energy is refracted or "bent". As the name implies, seismic refraction uses the travel times of refracted seismic energy to determine the seismic velocity of the earth. A short practical discussion of seismic refraction can be found here. The most important thing to keep in mind when learning how the seismic refraction method works is this: When doing seismic refraction, we are only interested in first-arrival energy at each geophone. The rest of the wave train -- reflected energy, surface waves, etc. are discarded and ignored. Except in the exceedingly rare case where the near-surface is slower than the speed of sound in Air, the first-arrival energy will always be either direct or critically-refracted energy. Common applications of seismic refraction include: Estimating rippability prior to excavation Mapping depth to bedrock/bedrock topography Mapping depth to ground water Measuring the thickness of the weathering zone Calculation of elastic moduli/assessment of rock quality Mapping thickness of landslides Identification and mapping of faults Seismic refraction uses body waves, most commonly, p-waves. Shear-wave refraction can also be done, but it has become largely supplanted by MASW. | |||||
| What is Snell's Law | 2 Relevance | 2 years ago | Gretchen Schmauder | General Seismograph Info | |
| Snell’s Law describes quantitatively how wave fronts refract or "bend" at boundaries between contrasting velocities. You've seen it manifest in light waves by the apparent bend of the straw in your glass of water; light travels slower in water than it does in Air. Refraction is well illustrated using Huygen's Principle. Consider a wave front (for our purposes, a seismic one) emanating from a point energy source, as shown in the animation above. For simplification, assume we are far enough from the energy source that the wave front is essentially planar, and is approaching an abrupt change in seismic velocity: Applying Huygen's Principle, we see that after time t, the plane wave has advanced a distance d equal to the radii of a series of spherical wave fronts emanating from the plane wave: The radii of the spheres, i.e., the distance the plane wave travels in time t, is equal to V1t. The tangent to the spherical wave fronts is the new position of the plane wave. The planar wavefront continues at velocity V1. Again applying Huygen, we see that "every point on the wave front" (see discussion of Huygen above) includes the points where the wave front intersects the velocity boundary: As the planar wave front advances, the velocity boundary becomes a new source of spherical wave fronts expanding at V2. Hence, part of the plane wave (the tangent to the spherical wave fronts emanating from the velocity boundary) is now traveling at V2. Note that within V2, its direction of advance has changed. This is because in V2, which is higher than V1, Huygen's spheres grow faster during time t. The refracted wave front continues in the new direction until another velocity boundary is encountered. Here is a simplified version at higher speed: Zooming out, we see the effect of this on a spherical wave: It should be obvious from the above that in order for a wave front to refract, it must strike the velocity boundary at an angle other than 90 degrees. It should also be obvious that in the case of V2 < V1, refraction will be in the opposite direction, and if V1 = V1, no refraction will occur. Snell's Law quantifies refraction in terms of angle of incidence and velocity contrast. Combining the above diagrams and adding rays, we can now describe Snell's Law: In the figure above, i is the incident angle, and r is the refracted angle, measured between the ray and a line perpendicular to the refracting interface. In the example above, the velocity contrast is positive; V2 > V1. There are numerous derivations of Snell's Law on the web if you wish to understand the math. From the equation, you can see that for any given positive velocity contrast, as i increases, r increases faster: This is important; it is the property of refraction that allows us to use refracted energy to measure subsurface velocities. Conversely, a negative velocity contrast results in refraction in the opposite direction: | |||||
| How fast do seismic waves travel and what controls this? | 2 Relevance | 2 years ago | Gretchen Schmauder | General Seismograph Info | |
| Different types of seismic waves travel at different velocities through any given material. In addition, different materials have different seismic properties, meaning that any one wave type can have a wide range of velocities, depending on the material properties. For instance, the p-wave velocity of shale can range from 800-3,700 m/s. Granite can range from 4,800-6,700 m/s. Because of this, by themselves, seismic velocities alone are not particularly diagnostic with regard to rock type. Ultimately, seismic velocity depends on the density and elastic properties of the material, whatever its composition. Specifically, Compressional-wave velocity depends on the “incompressibility” of the material, as embodied in the bulk modulus. The higher the bulk modulus, the less compressible the material, and the higher the p-wave velocity. Sound travels through water about four times faster than it does through Air. Similarly, shear-wave velocity depends on the rigidity of the material, or the resistance to shear. The higher the shear modulus, the higher the s-wave velocity. Mathematically, where K = bulk modulus µ = shear modulus ρ = density Note that Vp depends on both the bulk and shear modulus, while Vs depends only on the shear modulus. This observation implies two things: Shear waves always travel slower than compressional waves through a given material. Materials with zero rigidity – i.e., fluids – do not carry shear waves at all. Therefore, the absence or presence of groundwater has no effect on the shear wave velocity. It is interesting to note that, in general, seismic velocity increases with density – denser rocks tend to be much harder and faster. Yet in the above equations, density is in the denominator. This is known as the “velocity-density paradox”, the answer to which can be found in the fact that the elastic moduli tend to increase with density as well, and at a faster rate. | |||||
