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| # | Post Title | Result Info | Date | User | Forum |
| What is the "crossover distance". | 3 Relevance | 2 years ago | Gretchen Schmauder | General Seismograph Info | |
| The crossover distance is the distance from the source at which the critically-refracted energy from the next deepest layer overtakes the critically-refracted energy from the previous layer (in the two-layer case, the energy traveling through layer 1 is direct, not refracted energy, but the idea is the same). This is illustrated by the following animation: The direct energy (red) is the first-arrival energy at the first six geophones. However, by the seventh geophone, the direct energy is overtaken by the critically-refracted energy (green). The reciprocal of the slope of each segment is equal to the apparent velocity of the material. If there were a third, even faster layer, a third slope and second crossover distance would eventually appear on the travel time graph. The crossover distance, along with the velocities indicated by the slopes of the segments, are used to determine the refractor depth. | |||||
| Basic Troubleshooting Techniques for OhmMapper | 3 Relevance | 2 years ago | Gretchen Schmauder | Application | |
| 1. When the transmitter is turned on, the red power light (or Green light in later versions) comes on and stays on. The blue light will go into a rapid flashing pattern then settles into a three-flash sequence, for example short-long-short or short-long-long, or something like that. Is that what the transmitter is doing? If not, there are three possible causes of the problem and this will require require swapping parts: Defective dipole cable or shorting plugs are two potential problems. The best test is to plug the shorting plugs directly into both ends of the Transmitter and turn on. If this works, then add one dipole cable and turn on again. Then add the second cable and power up. If failure occurs with just the shorting plugs then the most likely problem is a battery with a shorted internal cell. This will look like it is fully charged when you measure it with a volt meter, but will not be able to supply the current required to drive the transmitter. Swap out batteries to test. If swapping the batteries does not resolve the issue and you never get the blue light to start flashing you may have a bad Tx and it would need to be returned to Geometrics. 2. When the receiver is turned on the red power light will come on, then the blue light will flash rapidly, then the blue light will turn off waiting for the receiver to phase lock onto the Tx. Once it locks onto the transmitter the blue light will start flashing at once per measurement. Depending on how conductive the ground is and how far apart the Tx/Rx separation is you may have to wait up to a minute to get the lock. Try it with about a 5 meter separation between the end of the dipoles, i.e. the equivalent to having a 5-meter rope between them. The Rx should lock and start flashing within about 20 seconds. If it never locks on even though the Tx's blue light is flashing then there may be something wrong with the receiver and it would need to be sent back. Remember that the transmitter blue light has to be flashing first. If the Tx is not working the Rx will never detect it and start flashing. 3. With the Rx turned on, even if the blue light is not flashing, when you look at the OhmMapper Test screen on the console do you see the message: Setting Gain, Phase A, Phase B or something similar being updated on the screen every second (or twice per second with the old systems)? If so your console is communicating with the receiver. If not, you have no communication between the Rx and the console so you could have a bad dipole cable, bad optical wand, bad console cable, or a bad receiver. If you have spares of any of these items you can troubleshoot the problem. If you have no spares then you will need to send the system back here for evaluation by submitting an RMA request. | |||||
| Battery percentage and status | 3 Relevance | 2 years ago | Magnetics SW | MagEX | |
| Overview The MagEx instrument and the MagNav app both display information about the state of the instrument's battery. Battery state and reporting exist in bands according to percentage of remaining battery capacity: 30% or higher:The instrument has good remaining capacity.The LED on the instrument's power switch glows a solid Green.MagNav displays the battery percentage or voltage in black text on a white background. Between 20% and 30%:The instrument has capacity to survey for additional time, but if you will be surveying a significant amount more, start thinking about changing the battery.The LED on the power switch is blue.MagNav displays the battery percentage with a blue background. Between 5% and 20%:You can continue to survey, but the battery is running low and you should consider changing the battery soon.The LED on the power switch is red.MagNav displays the battery percentage with a red background, and periodically notifies you that the battery is running low. Below 5%:The battery is running low, and the instrument may turn off at any time in order to preserve battery health. You should change the battery as soon as possible. Temperature-related effects:Battery performance also changes as the temperature of the battery changes; as the temperature of a battery falls, the voltage it supplies also decreases, and the total energysupplied by the battery decreases. This means that in cold weather a battery will not last as long as in hot weather. The battery percentages reported in the instrument are adjusted for the effect of temperature; at a given battery voltage a cold battery will display a higher percentage than a warm battery will report. The effects of colder temperatures are not normally permanent; as a battery warms up, its output voltage and energy return to higher levels. Notes about the calculation:The MagEx instrument includes 2 batteries, and each battery includes 3 separate cells. Battery percentages are calculated from only one battery in the instrument - either the single battery if only one is connected, or from the better battery if two batteries are connected. Reported battery percentage is an estimate, based on measurements of the behavior of healthy batteries in instruments in the field and in the lab. Battery performance may change as a battery ages and as the temperature changes. The best practice for batteries is to use 2 healthy, fully charged batteries, and replace them both when the percentage falls below 20%. | |||||
| How do I magscreen parts (make sure they are magnetically clean) which will be integrated with my MFAM Dev Kit? | 3 Relevance | 2 years ago | Rui Zhang | Application | |
| In general, avoid stainless steel parts. If you have to use stainless steel parts, make sure it is made of SS316. To make sure that the parts are magnetically clean, you can set up the MFAM Dev Kit in the gradiometer mode. 1. Have the two sensors separated by 20cm or more. 2. Turn on the gradient reading (green curve) in MagViewMFAM. 3. Place the part 10cm to one sensor and 30cm to the other. 4. Rotate the part while monitoring the gradient curve. Make sure you don't have any magnetic parts (such as keys, cell phone, watch) with you while doing this. 5. The peak-to-peak difference in the gradient curve (you may have to adjust the gradient scale if the curve wraps on screen) is the magnetic signature of the part at 10cm. 6. For the magnetic signature at different distances, scale the reading as 1/R^3. For example, if the part will be 20cm away, its magnetic signature should be 1/8 of of the reading at 10cm. | |||||
| Magnetometer Base-Station | 3 Relevance | 2 years ago | Rui Zhang | General Magnetometer Info | |
| Color representationRed: data collected by a survey magnetometer, such as a MagArrowGreen: survey data we are interested inBlue: base-station data Magnetic field is a function of location (r) and time (t): B(r,t)In general, we are only interested in magnetic field as a function of location: B(r). Ideally, we set up one magnetometer at each location of interest and measure the magnetic field at different locations at the same time. This method removes the time dependence.However, the method requires many magnetometers. The common practice is to move one magnetometer around. In this case, B(r,t) is collected since it takes time to move the magnetometer. To remove the time dependence, a base-station is required. Assume the base-station reading at a fixed location R1 is B1(R1,t) = c1 + B1(t), where c1 is a constant, depending on R1. We hope to achieve the base-station correction B(r,t) - B1(R1,t) = B(r) – c1.For a single base-station location, c1 can be ignored since it is a constant offset applied to the whole survey area. In another word, B(r) and B(r) – c1 generate the same survey color map. For large scale surveys, it is impossible to have a single base-station location, since it is not economical and magnetic field time dependence is also regional.Now we obtain base-station data sets at different locations: B1(R1,t), B2(R2,t), B3(R3,t)… When the base-station correction is applied, Bi(r,t) - Bi(Ri,t) = Bi(r) – ci. In general, ci are different. Therefore, Bi(r,t) - Bi(Ri,t) can NOT be combined directly into a single data base unless constant offsets are applied to achieve Bi(r). A typical combined 5-day survey without applying offsets is shown below. These constant offsets are hard to measure, unless multi base-stations are set up. However, they can be calculated based on the overlapping areas between two data sets since the readings in the overlapping areas must be the same, assuming the same AGL (above ground level). With this method, the new combined data is shown below. Geometrics offers an auto survey combination program for MagArrow and MagEx customers. Attachment : Survey_Data_Stitch_Auto_V3.zip | |||||
