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| # | Post Title | Result Info | Date | User | Forum |
| What is degaussing? How can I degauss metallic components for my magnetometer setup? | 6 Relevance | 3 years ago | Gretchen Schmauder | General Magnetometer Info | |
| Degaussing is a method by which magnetic domains in metals or magnetic inclusions in other materials are randomized so that net magnetization is minimized. One tool do accomplish this is the “Bulk Tape Eraser” designed to erase data tapes. The method works because the “Bulk Tape Eraser” generates an alternating electromagnetic field, which flips the magnetization of the magnetic domains in the material at 100 or 120 reversals per second (50 or 60 hertz). As the operator slowly removes the “Eraser” from the vicinity of the magnetized material, the magnetic domains of the material individually freeze in one orientation or the other, leaving the domains in a randomized orientation with minimal net magnetic effect. Degaussing with a Bulk Tape Eraser *The procedure is straight forward. Plug the Eraser into an extension cord or wall socket (the Eraser cord is usually short). Holding the object to be degaussed in one hand, depress the Eraser start button and move it towards the object. Once close to the object or section of material, begin moving the Eraser with a small circular motion and then increase the radius of the circle as you draw the Eraser away from the object. DO NOT STOP the Eraser closer than three feet from the object being degaussed or it will become strongly magnetized in one direction! If this happens accidentally, just redo the degaussing procedure over again starting from the beginning. *For larger objects, run the Eraser along tubing or struts in a circular motion to “bathe” the objects in an oscillating field. Be sure to cover the entire surface area of the object being degaussed. Then slowly withdraw the eraser (while still running) until it is at least 3 feet away. Then release the power switch. *The magnetometer can be used to check the sufficiency of the degaussing procedure. After degaussing, rotate the object close to an operating magnetometer to see if there is a response from the magnetometer. This is best done with a cesium magnetometer operated in gradient mode, but it can be done with a single Sensor with one person watching the result and another moving the object near the Sensor. Degaussing Sensor Mount Degaussing Pack Frame Degaussing GPS Antenna Limitations of Degaussing with a Bulk Eraser Depth of penetration: The Bulk Tape Eraser can only randomize materials to a certain depth. This is due to the size of the gap in the degaussing unit. A small gap makes for a very large degaussing field at the gap (about 2000 gauss, or 200 million nanoteslas), but also for a very rapid falloff away from the gap. Bulk tape erasers are optimized to penetrate through the thickness of a typical video tape. This gives a typical depth of an inch (2.5 cm). Deeper objects may need to be degaussed Using stronger degaussing fields. Degaussing through a conductive chassis: An additional problem occurs when the object being degaussed is covered by a conductive surface (such as a sheet of aluminum). The degaussing field will generate huge eddy currents in the conductive surface which will generate its own opposing magnetic field. This will be evident to the operator because the opposing field will cause the degausser to buzz loudly. This doesn’t hurt anything, but be aware that the degaussing field on the other side of the conductive surface will be attenuated by some amount, so it may take a longer amount of time or multiple passes to degauss the object. The Bulk Tape Eraser is a short duty cycle device. It varies a little from manufacturer to manufacturer, but typically it is rated for 1 minute on and 5 to 10 minutes off. Most have an internal thermal cutout that will shut it off if it overheats, and if tripped may take 20 minutes or more to cool down enough to reset. Frequently Asked Questions Why is degaussing needed? Degaussing misaligns magnetic domains so that there is no net permanent magnetization that would give an offset or heading error to magnetic field readings. Sensitive magnetometers such as those manufactured by Geometrics can be effected by nearby materials that are not sufficiently magnetically randomized. Degaussing does not alter the induced magnetic moment of any material. A piece of steel, when degaussed, is still magnetic because it draws and concentrates the earth’s field through it. However, a degaussed piece of steel is much less magnetic than a permanently magnetized piece. How much effect does it have on magnetic signatures? Depending on the distance from the Sensor to the magnetic object and the amount of magnetization, the effects can be very large -10’s of nanoTeslas. Many materials including brass, aluminum, fiberglass and other non-ferrous materials may have some ferrous materials in them naturally or acquired during the manufacturing process. Other materials such as ‘non-magnetic’ stainless steel are hugely magnetic when compared to the sensitivity of our magnetometers. Degaussing can decrease the magnetic effect of these materials by a factor of 10 or more. What should I degauss? The operator should degauss any metallic object that is near the Sensor. By “near”, in general we mean within 1 meter but certainly those metallic and non-metallic materials within a few centimeters of the Sensor must be considered (this also includes the Sensor itself, which could have minute magnetic inclusions in the Sensor materials). This could also include GPS antennas, magnetometer cart assemblies (including brass fittings, bolts, clamps), buckles, eyeglasses, boots and parts of backpacks. We would also do occasional degaussing of the G-858 console and batteries. Will degaussing hurt anything? This is a tough question since it is impossible to imagine every conceivable system arrangement that could be subjected to degaussing. In all our experience we have never had any electronics device hurt by the degaussing process. This is because the induced voltages from the degausser are low, and the electronics components have a fairly high impedance at low voltages. It would be safer to degauss electronics while the power to the electronics is turned off in case the small induced voltages cause the device to operate incorrectly. It is always safe to degauss any of Geometrics’ manufactured equipment (including the Sensor). On the other hand, here are some things to consider when degaussing some types of objects. Large conductive planes or rings will have large circulating currents induced in them by the degausser (but the voltages are still very small). This induced current will produce an opposing magnetic field that will fight the degaussing field – causing both the degausser and the conductive plane/loop to vibrate substantially. If the device being degaussed is sensitive to this vibration (intricate mechanical workings and the like) then this is a possible route for causing some damage. Also, sometimes objects being degaussed have embedded magnets that are necessary for the device to operate properly. A good example is a device with a permanent magnet speaker inside. Generally it is hard to degauss a magnetically hard permanent magnet, but the degausser is strong enough to at least partially do the job. A partially degaussed speaker (or other object that requires a magnet to work right) isn’t going to work the same as before – so be aware. [Things that have magnets in them shouldn’t be used near magnetometers anyway.] When to degauss and how often? We recommend that parts close to the Sensor be degaussed before every major survey event. In other words on a weekly or monthly basis or before a new survey. Remnant magnetism or “Perm” can be “picked up” (domains realigned) when the materials are static in the earth’s magnetic field for a period of time. The amount of time required to acquire a “Perm” can be from days to weeks or months depending on the magnetic “hardness” of the materials. This is also known as the materials “susceptibility”, that is, susceptibility to being magnetized. Also, magnets are everywhere, and they can easily and unknowingly ‘perm’ up parts on or near the Sensor. Magnetic screwdrivers, for example, are great for holding steel screws on the end of the driver while starting them into a threaded hole, but they are bad news near any magnetometer Sensors. | |||||
| Understand Dead-zone, Heading Error, and their importance for the MagArrow | 5 Relevance | 3 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. | |||||
| Sensor box SD card | 4 Relevance | 2 years ago | Andre Santos | G-864 | |
| I was doing a survey, and the tablet lost connection with the Sensor, with no data being saved to the tablet. So I took the SD card of the Sensor box, hoping that the data was kept there at least as a backup before the survey ended and data was completely transferred to the tablet. But there is nothing on the SD card. It is empty instead of having a LOST.DIR folder that is also empty.So, my question is, what is the Sensor box SD card for?Second, is there a way to prevent tablet disconnection from the Sensor WIFI (which happens frequently) and backup data when this happens? | |||||
| Does using a magnetometer pose a health risk? | 4 Relevance | 3 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. | |||||
| Cesium Magnetometer Sensor Bandwidth | 4 Relevance | 3 years ago | Gretchen Schmauder | Hardware | |
| The subject of "Bandwidth" comes up often when discussing cesium magnetometers. There are two different aspects of bandwidth that are different and need to be differentiated: The cesium magnetometer uses an atomic resonance of the Cs 133 atom (see note 1 below) which varies proportional to the ambient magnetic field. This atomic resonance is used to set/control the frequency of an oscillator. Therefore the output signal from the magnetometer is a *frequency* which is proportional to the earth's magnetic field at a coefficient of 3.498572 Hertz per nT. Thus the output frequency (called the Larmor frequency) varies from roughly 70KHz at the equator to 350 KHz at the poles. Because the cesium magnetometer is an oscillator, and because phase is important in an oscillator, the "Bandwidth" of the electronics in the magnetometer must be at least 10 times higher than the maximum output frequency of 350 Khz, or roughly 3.5 MHz. This bandwidth should not be confused with the magnetic field measurement "Bandwidth", or how fast of a magnetic field change can be measured. To put a scaler value on any magnetic field reading the output frequency of the magnetometer must be counted, and then scaled appropriately to get a field reading in nanoTeslas. The counting process involves opening a gate period, counting the number of Larmor (frequency) cycles that occur, divide that number by the precise time interval of the gate period. then scale that value by dividing by the 3.498572 Hz / Larmor coefficient. You get one reading per gate period, which by default is five or ten hertz (200mS to 100 mS gate period). What you get for a reading during any gate period is the time interval average of the Larmor frequency over that period. The transfer function of a "time interval averaged" signal is [sine(x) / x] with the first zero falling at the sample frequency. Thus if the G-882 is sampling at 10 hertz the maximum resolvable magnetic field change is roughly 5 hertz. The sample interval of the G-882 is adjustable by sending commands to it. If the sample rate is set to 20 hertz the measurement bandwidth will double (from a 10 hertz sample rate) but the base line noise will go up as well. It should also be noted that the basic system noise level of the G-882 for a stationary Sensor is set by the counter resolution - not by the signal to noise ratio of the oscillator electronics. If the Sensor is tilted away from its optimum orientation the magnetometer signal will decrease (and therefore the signal to noise ratio), but the counted field output will not show any significant degradation until the Sensor is approaching the dead zone (where the signal is really low). | |||||
| Cesium Magnetometer Sensor Bandwidth | 4 Relevance | 3 years ago | Gretchen Schmauder | Hardware | |
| The subject of "Bandwidth" comes up often when discussing cesium magnetometers. There are two different aspects of bandwidth that are different and need to be differentiated: The cesium magnetometer uses an atomic resonance of the Cs 133 atom (see note 1 below) which varies proportional to the ambient magnetic field. This atomic resonance is used to set/control the frequency of an oscillator. Therefore the output signal from the magnetometer is a *frequency* which is proportional to the earth's magnetic field at a coefficient of 3.498572 Hertz per nT. Thus the output frequency (called the Larmor frequency) varies from roughly 70KHz at the equator to 350 KHz at the poles. Because the cesium magnetometer is an oscillator, and because phase is important in an oscillator, the "Bandwidth" of the electronics in the magnetometer must be at least 10 times higher than the maximum output frequency of 350 Khz, or roughly 3.5 MHz. This bandwidth should not be confused with the magnetic field measurement "Bandwidth", or how fast of a magnetic field change can be measured. To put a scaler value on any magnetic field reading the output frequency of the magnetometer must be counted, and then scaled appropriately to get a field reading in nanoTeslas. The counting process involves opening a gate period, counting the number of Larmor (frequency) cycles that occur, divide that number by the precise time interval of the gate period. then scale that value by dividing by the 3.498572 Hz / Larmor coefficient. You get one reading per gate period, which by default is five or ten hertz (200mS to 100 mS gate period). What you get for a reading during any gate period is the time interval average of the Larmor frequency over that period. The transfer function of a "time interval averaged" signal is [sine(x) / x] with the first zero falling at the sample frequency. Thus if the G-882 is sampling at 10 hertz the maximum resolvable magnetic field change is roughly 5 hertz. The sample interval of the G-882 is adjustable by sending commands to it. If the sample rate is set to 20 hertz the measurement bandwidth will double (from a 10 hertz sample rate) but the base line noise will go up as well. It should also be noted that the basic system noise level of the G-882 for a stationary Sensor is set by the counter resolution - not by the signal to noise ratio of the oscillator electronics. If the Sensor is tilted away from its optimum orientation the magnetometer signal will decrease (and therefore the signal to noise ratio), but the counted field output will not show any significant degradation until the Sensor is approaching the dead zone (where the signal is really low). | |||||
| How do get live data streaming from UART5 or ethernet port without using MagView. | 3 Relevance | 2 years ago | Kuldeep Dhiman | Application | |
| Hi guys, I need MFAM live data streaming from ethernet or serial UART5 for my project. Initially, I am planning to write a piece of code Using C++ that reads the data from one of the ports and prints it on the terminal. To be sure that data is present on UART5, I connected this port to the USB port of my laptop Using a suitable cable and tried to monitor data Using Putty with different baud rates but found nothing. Is data streaming available on UART5 by default? or do I need to enable it? I can see data on the ethernet port Using MagView. Ethernet port uses TCP protocol. Is there any way to enable UDP on the ethernet port? In case I write code to read the ethernet port Using TCP then please suggest a suitable reference to start. Thanks a lot | |||||
| MagArrow Heading Error Compensation Flight FAQ | 3 Relevance | 3 years ago | Gretchen Schmauder | Application | |
| To perform a heading error compensation flight, fly the UAV with MagArrow attached up to 100-150 meters in a low gradient area. Hover the drone in a single spot and rotate it slowly through 360 degrees while logging magnetic data the with MagArrow. By keeping the drone location stationary the mag field will be also be constant. Thus we are only left with the Sensor reading as a function of orientation. The MagArrow has two MFAM Sensors, and the way they are arranged ensures that when one Sensor is in its dead zone the other is at its optimum orientation, and vice versa. The readings from the two Sensors are combined to produce one magnetometer reading only. The two Sensor readings are weighted such that as one Sensor approaches its dead zone it is weighted much less (down to zero in the dead zone) while the optimum oriented Sensor is weighted more fully. Thus you get only one magnetometer reading with no dead zones whatsoever. In addition, the weighted averaging of the Sensors still does partial heading error cancelling. | |||||
| Baseball Caps Create Magnetic Anomalies | 3 Relevance | 3 years ago | Gretchen Schmauder | General Magnetometer Info | |
| If you perform a land magnetometer survey and you see random spikes in the data spread out over many cycles, these being real magnetic events, then the issue might not be the Sensor but metal on your person. A baseball cap often has a little steel button on the top, and for land magnetometers where the Sensor is overhead, this steel is very close to the Sensor. With movement during walking, this can create strong magnetic spikes in the data. To test this, you can mark the location of the magnetic Sensor in relation to the steel button on a baseball cap and record the magnetic field standing still. Then lower the Sensor 1 meter and you'll observe the anomaly increase by a factor of 16 or so. For magnetometer surveys, it is important that the operator is free of electronics and metal. This means no cell phone, no belt, no steel toe boots, etc. Small quality checks can have a big impact on the data and save time in the field. | |||||
| Using a Geode Seismograph to quantify vibrations | 3 Relevance | 3 years ago | Gretchen Schmauder | Application | |
| We get occasional calls asking how to use one of our seismographs as a vibration monitor. The method for this is described below, but it should be noted that while true amplitudes can be obtained, this method of measuring them would probably not stand up in court. True vibration monitors – seismographs designed specifically for this task – have a built-in geophone. The voltage output of the geophone per unit vibration is known to a very high degree of accuracy, and the system is calibrated by the manufacturer regularly (usually once a year). If you are measuring vibrations in a situation in which litigation might be involved, you should use a true vibration monitor. One of the more popular ones is the Blastmate by Instantel. Vibrations are generally quantified in units of particle velocity, the first derivative of displacement. Geophones are particle velocity Sensors – output is directly proportional to particle velocity. If you know the response function (sensitivity) of your geophone – the voltage output per unit velocity input – you can convert voltage (as measured by the seismograph) to mechanical vibration in terms of particle velocity. The sensitivity of your geophone can be obtained by the geophone manufacturer, and will be expressed as a function of frequency. A typical graph of geophone sensitivity is shown below: It is best to used a geophone that has a natural frequency at or lower than the lowest frequency of interest. Seismic data files are stored in a SEG format. The first step is to convert the SEG output of the seismograph to an ASCII columnar format. If you are Using an ES-3000 or Geode, your controller PC should have this icon for Tape Reader on the desktop: If not, download Tape Reader. Run the program and click on File>>Open: Read in the file you wish to convert to ASCII. Now, click on File>>Save Displayed Data to Ascii File: After making your format choices (be sure to convert to mV), press Export. The record will be written in an ASCII format that can then be imported to Excel. From here you can calculate the frequency spectra and particle velocities Using the response function of the geophone. | |||||
| Do Cesium Vapor Magnetometers Require Calibration | 3 Relevance | 3 years ago | Gretchen Schmauder | General Magnetometer Info | |
| Our cesium-vapor magnetometers do not require periodic calibration in order to maintain the accuracy as described in our published specification when the instrument is operated within specified environmental ranges. Geometrics cesium-vapor magnetometers are manufactured and tested based on the discoveries and the basic designs of Carian Associates (U.S. Patent 3,071,721). This method of total magnetic field measurement relies upon the measurement of the optical absorption of a particular cesium spectral frequency by the cesium vapor enclosed in a small glass cell. This method is similar to those used in the measurement of atomic emission and absorption frequencies Using spectroscopic reference cells. The technique thus relies on well-known fundamental quantum mechanical constants for accurate and precise measurement of the magnetic field. As a result, no adjustments to the Sensor are needed in order to correct or maintain its accuracy and Geometrics Sensor and Sensor driver electronics are designed to either work correctly or to not work at all and to report both the strength of the magnetic field as well as the strength of the electrical signal produced by the working Sensor. In this way, the signal strength measurement provides a direct indication of the operational state of the magnetometer while it is running and serves to alert the operator if the magnetometer encounters environmental conditions that are outside of its operating range. Occasional maintenance of the instrument at Geometrics facility should be performed when the instrument's internal diagnostics indicate substandard performance as described in the operator's manual. Please contact Geometrics Support for technical advice and additional information pertaining to your specific model. | |||||
| What are the differences between LCS050G (Low-Noise) vs. LCS100S (SuperMag) modules | 3 Relevance | 3 years ago | Gretchen Schmauder | Hardware | |
| Differences between LCS050G (Low-Noise) vs. LCS100S (SuperMag) modules Q. What is the difference between LCS050G (Low Noise) and LCS100S (SuperMag)? Is different firmware the only thing that separates the Low-Noise version from SuperMag version? Or are there mechanical differences in how the Sensors are constructed? A.The firmware is different, but that is not the only difference. We also build our Sensors in two different groups - A and B - to satisfy the different requirements for each version. Group A satisfies SuperMag specs, while group B meets the Low-Noise specs (please refer to the datasheet). Each SuperMag must have 2 Group A Sensors. Q. The Sensors in the SuperMag are physically mounted in a configuration to eliminate the dead zones. Could a customer mount their Low-Noise version of the Sensors into the same 'no Dead Zone' configuration, then run a simple script to accept only good data so that if one Sensor goes into a dead zone, the firmware will automatically switch to record the data from the second Sensor? Obviously Geometrics performs some magic when combining the data in the firmware, but that doesn't necessarily preclude a customer from trying to make a "SuperMag" type system with their Low-Noise Sensors, right? A. In principle, yes. Customers can write their own script to combine the readings from each Sensor to achieve the dead-zone-free operation. However, smoothing out the combined reading when one Sensor’s reading drops out is pretty tricky. In addition, the heading effect will be much worse (determined by the heading effect of individual Sensors) if customers choose to combine individual magnetometer readings instead of Using the SuperMag dead-zone-free mode. Q. Can I upgrade my Low-Noise Sensors to the SuperMag version? Would I have to send my unit to Geometrics' Customer Support or could you simply provide the new firmware so that the instrument behaves like a SuperMag? A. Yes, it is possible to upgrade your firmware, but this process requires you to return the instrument to us. However, Geometrics will NOT guarantee the SuperMag specs in this case since LCS050G still has Group B Sensors. The only way to guarantee SuperMag specs is to purchase the SuperMag Sensors. Please contact us us for more information. | |||||
| Using and Charging the MagEx LiPo Battery | 3 Relevance | 2 years ago | Gretchen Schmauder | Hardware | |
| This link takes you to a short video on properly Using the Lithium Polymer (LiPo) battery. | |||||
| RE: How do get live data streaming from UART5 or ethernet port without using MagView. | 3 Relevance | 2 years ago | Rui Zhang | Application | |
| @kuldeep, No, the data streaming is ONLY through the Ethernet port, not the UART5 port. Current instrument software does not support the UART5 streaming. An example C code to stream MFAM data through the Dev Kit Using TCP protocol can be found at: | |||||
| Stacking waveform data (SEG2) files using Pickwin | 3 Relevance | 3 years ago | Gretchen Schmauder | Software | |
| Stacking waveform data (SEG2) files Using Pickwin Make sure your dimension size is large enough. To start, select "option", then "Dimension size". If the maximum traces is smaller than the total number of traces, increase the maximum traces, check “Change dimension size” and click “OK” to change dimension size. Open one waveform file as usual. Open another waveform file as usual. Choose “Append to present data”. If you want to change the color of traces depending on files, change component (2 to 10), check “Change” and click “OK”. Note that color does not affect stacking. Trace color is shown below. If you uncheck the “Change”, all traces are shown black. Confirm total number of traces. Two waveform files are shown together. Make sure there is no time difference between shots. After importing 3rd file. After importing 4th file. Make sure there is no time difference among shots. Confirm total number of traces.. All waveform files are shown together. Make sure there is no time difference among shots. Select “Processing”, “Vertical stack”. Select “a. Average” and click “OK”. You may select “Semblance” or “Semblance weighted stack” to emphasize coherent signal. Stacked data is shown. | |||||
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