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| # | Post Title | Result Info | Date | User | Forum |
| Is it possible to extend the cables between the MFAM sensors and module? | 2 Relevance | 2 years ago | Gretchen Schmauder | Hardware | |
| The cables between the sensors and the MFAM module are flexible circuit boards, and the length is limited to 20 inches. It is possible to remove the MFAM module from the Development kit box and then reconnect it using a ribbon cable. That would allow you to extend the MFAM module and sensors away from the Dev Kit box. Our engineers have tested it to 4 meters. Below are some details about the ribbon cable. The connector on the MFAM unit is Samtec FSH-110-04-F-DH. Its mating connector is Samtec SFMH-110-02-L-D-WT. The easiest option for an extender cable between the MFAM and the Dev Kit is a pair of cable assemblies from Samtec www.samtec.com which has male/female mass terminate connectors put onto a ribbon cable. These connectors plug directly into the MFAM I/O connector and also into the Development Kit. We are comfortable with lengths to 10 feet Total. The samtec P/N for this cable is: FFMD-10-T-60.00-01-F-N The ‘60.00’ number specifies the cable length in inches (which equals 5 feet). We have found that there is generally a 2-4 week lead, time since they are made to order and not an off-the-shelf part. (There is another solution as well if you want to make adapter boards at each end (Dev Kit and MFAM). The exact Samtec mates for the MFAM / Dev Kit connectors are made in PCB mount connectors only, so if you make simple small adapter board to adapt the samtec connector to another connector of your choice. We've done this with ExpressPCB which is fast and inexpensive. A board set from ExpressPCB is about $70 including shipping. Our Engineering Team has a design and parts list they can send you if you're interested in going this route.) | |||||
| How many channels do I need for Seismic Reflection surveying? | 2 Relevance | 2 years ago | Gretchen Schmauder | General Seismograph Info | |
| There is no one right answer to this question. The higher the channel count, the higher the fold (for any given shot interval), and the higher the signal/noise ratio. For land seismic, we generally recommend 24 or higher-fold data. If the shot spacing is equal to the geophone spacing (typical), this means that you must record on at least 48 channels with each shot. In addition, you must have extra channels for electronic rolling. Taken together, this means that for land CDP reflection, you should have a minimum of 72 channels, which will allow you to roll 48 live channels through a Total of 72. | |||||
| Understand Dead-zone, Heading Error, and their importance for the MagArrow | 2 Relevance | 2 years ago | Gretchen Schmauder | Application | |
| Dead-Zones The MagArrow is a dual sensor magnetometer powered by MFAM sensors, but it is configured for use so it only has a single data output. The reason Geometrics has done this is so we could ensure the MagArrow encounters no "dead-zones". A dead-zone occurs when the orientation of a magnetometer results in the magnetometer producing poor or no measurements. The dead-zone angle depends on the location of survey. Since we have the two MagArrow MFAM sensors in orthogonal orientations, the MagArrow Magnetometer has operability worldwide without affecting survey orientation, making it much easier to use for the customer. Heading Errors Heading errors are a type of noise magnetometers can experience. They come from three sources: Sensor Console Operator Magnetic materials in the sensor itself are the primary cause of heading errors. The physics of Cesium and Potassium magnetometers can contribute small amounts to the Total heading error. Magnetic contamination near the sensors, operating electronics, or operator can all contribute to heading error. Heading errors look like herringbone patterns in survey images. Alternate lines can also be corrugated. Dead-Zones vs Heading Errors while these two sources of error in magnetic data are different, there is overlap between them when operating a magnetometer like the MagArrow. Heading errors can be fixed relatively easily in software, where dead zones can be much harder to manage. If a line is completely ruined because of a dead zone then they will need to re-fly the line/mission which is time consuming. Even with advanced users, these sorts of mishaps can happen. Additionally, the closer a mag sensor operates to a dead-zone, the larger a heading error will be measured. With compensation software and a pre-survey heading error flight, heading error can be reduced dramatically to around 1 nT for the MagArrow. Click to view the difference between Raw and Processed MagArrow Data The MagArrow is only outputting a single value as a means to create a “no-dead-zone” system. Obviously each sensor has a dead zone themselves, but with the sensors orientated orthogonally at least one sensor at all times will have a magnetic measurement. By combining the measurements from both sensors it is possible to generate a constant magnetic field measurement independent of orientation and location in the world. If the data from each MFAM sensor in the MagArrow was individually reported there would be gaps in the mag fields observed by either sensor as you fly, rotate, and swing. | |||||
| Battery percentage and status | 2 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%. | |||||
| What are the differences between the standard MFAM and the SX version? | 2 Relevance | 2 years ago | Gretchen Schmauder | Hardware | |
| The only difference between the standard and SX version is the sensitivity is 4pT/rt-Hz and 20 pT/rt-Hz respectively. Here is an expected response with the magnetometer moving past a generic magnetic projectile: In this case the amplitude is about 1nT in Total from peak to peak. The feature itself is quite distinguishable. This is assuming there is no noise in the system. Here is what the data looks like with 4pT/rt-Hz noise: You can see the general structure is still there but there is a little more wiggle on the trace that is associated with the noise of the system. Here is the data with 20 pT/rt-Hz noise: Again, here the structure is clearly visible but the data looks a bit noisier. With some signal processing technique, such as low pass filtering, noises can be further reduced. Please note that in real surveys, detecting 1nT peak-peak anomalies is always a big challenge even with the most sensitive magnetometers due to other noise sources, such as motion noises and environmental noises. Therefore, SX version is in general NOT the limiting factor for conducting surveys. To understand this concept better, you can use the magnetic gradient tool developed by our partner in the UK, Geomatrix Earth Science. | |||||
| Why do we see less structures in MagArrow surveys, compared with land magnetometer surveys? | 2 Relevance | 2 years ago | Rui Zhang | General Magnetometer Info | |
| This is most likely due to the fact that land surveys are typically much closer to the ground (therefore closer to targets). Two spatially separated magnetic anomalies can be resolved on the ground but not several meters above the ground, as shown in the simulation plot below. The simulation is for two targets, separated by 4m, located at z= -2m, y=3m, x= 0m and z=-2m, y=7m, x=0m. The Total magnetic signal on the x=0 plane from the two targets are plotted in 2D as a function of y and z (with z=0 being on the ground). For land magnetometer surveys, z = 0.5m or less. If we draw a line at z = 0.5m (survey line), it is clear that there will be 2 peaks in the sensor reading along y direction as long as the magnetometer has a high enough sample rate. Therefore, the two targets can be resolved. For MagArrow surveys, if the above ground level (AGL) is >3m, the two targets cannot be resolved no matter how high the sample rate is. This simulation also indicates a rule of thumb about the linespacing in MagArrow surveys. The linespacing should be about 1-2 times the AGL. Less than the AGL will not produce any higher resolution map. The simulation plot provides customers with a general idea of how fast the magnetic signal decays as a function of distance from the target. The signal falls as 1/R^3. | |||||
| What are the differences between the standard MFAM and SX Versions | 2 Relevance | 2 years ago | Gretchen Schmauder | MFAM | |
| The only difference between the standard and SX version is the sensitivity is 4pT/rt-Hz and 20 pT/rt-Hz respectively. Here is an expected response with the magnetometer moving past a generic magnetic projectile: In this case the amplitude is about 2nT in Total from peak to peak. The feature itself is quite distinguishable. This is assuming there is no noise in the system. Here is what the data looks like with 4pT/rt-Hz noise: You can see the general structure is still there but there is a little more wiggle on the trace that is associated with the noise of the system. Here is the data with 20 pT/rt-Hz noise: Again, here the structure is generally there but the data looks quite a bit noisier. So for smaller targets or more subtle anomalies they can be obscured or missed entirely. To understand this concept better, you can use the magnetic gradient tool developed by our partner in the UK, Geomatrix Earth Science. | |||||
| How Far Can a Magnetometer 'See'? | 2 Relevance | 2 years ago | Gretchen Schmauder | General Magnetometer Info | |
| Total field magnetometers like the optically pumped cesium magnetometer are passive devices, they do not send out waves or pulses. They measure distortions in the earth’s normally homogenous magnetic field and can sense distortions due to ferrous objects at great distances. The basic rule of thumb is that one ton (1000 Kg) of steel or iron will give us a 1nT anomaly at 100 ft. or 30m. Since the amount of distortion falls off as the cube with distance (compare a metal detector which falls off as the inverse 6th power!) and is linear with mass, every time we cut the distance in half, we can see 1/8th the mass. Therefore, we can sense 250 lbs. (100kg) at 50 feet (15m), or 30lbs (15kg) at 25 feet (8m), or 4lbs (2kg) at 12 feet (4m). However this is not the whole story. The factors given above are for induced magnetic fields only. Many targets also have remnant or permanent magnetic effects (meaning they have become magnetized either in production or by the earth’s field) and can therefore have larger anomalies by a factor of 3 or 5 or more. Also many hollow objects like barrels or other tubular structures appear as though they are solid due to self-shielding from the earth’s field, and thus have much larger anomalies than their mass would predict alone. Pipes fall off as the inverse square and are thus detectable at even greater distances. Please see our Applications Manual for Portable Magnetometers for more information. | |||||
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