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| # | Post Title | Result Info | Date | User | Forum |
| RE: Geometrics preliminary MagArrow and MagEx data processing program download | 6 Relevance | 2 years ago | Ahmed Ramadan | Software | |
| Hello Dears, I'm new to Geometrics products and interested in MagArrow. I have some questions please. As a geophysicist, I examined the attached data and applied heading compensation to the measured data. My questions are after applying the 4th difference filter (the last Panel in the attached figure) which is very important for measuring data noise especially comTing from the drone. I found the range to be very high and exceeding +/- 0.1, even after applying low pass filter to reduces the sampling rate of data from 20 Hz to 10 Hz. I think one of the biggest advantages of the MagArrow is that the sensor is suspended 3 meters below the drone to cancel out the effect of the noise coming from the drone, so I need to explain that. Attachment : 4th difference.jpg Secondly, in the attached file of the survey, the range of the total magnetic field data is about 43,000 nanoTesla, while when calculating the IGRF for that region based on longitude and latitude, I found that the range is about 49,000 nT, which is very far from the measured data? Could you please explain to me the answers to these questions because our goal is to explore minerals and not UXO. Kind Regards, Ahmed | |||||
| What is degaussing? How can I degauss metallic components for my magnetometer setup? | 6 Relevance | 2 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. | |||||
| RE: Rs232 Comms to maggy | 4 Relevance | 1 year ago | Lynn Edwards | G-882 | |
| I have set up a G-882 system here at Geometrics and am receiving data and sending commands using TeraTerm (any terminal emulation program should work). When in normal use mode the Digital add on board sits in front of the G-882 and parses and acts on all commands coming in. There are two versions of the Digital Add On board, which are the GP120 and the GP140. The GP140 is a newer version of the Digital Add ON board. It is the GP140 Digital board that outputs all S/N (and other) information. I first set up with the GP140 board (the newer version). I find that the ""RESET" command does work - i.e. it goes into BYPASS mode for a couple seconds, then output the S/N and configuration information, and reverts to normal operation with the digital depth and altimeter information. But it only works every other time I send it. The first time nothing happens. Then I send it again and it works. This appears to be a bug in the GP140. For some commands the first command after power up or reset are ignored. The second time (and subsequent commands) are executed. The work around seems to be sending the RESET command twice. I also tried an older G-882 with the GP120 Digital board. The Reset (and other commands worked first time and every time. BTW, the Digital Board version is in the second line with the S/N information that is sent on power up or Reset. Some questions: 1) My configuration is one G-882 connected to a PC through the White junction box. Is this your configuration, or do you have concatenated G-882's? 2) Can you get the G-882 to accept any commands (like going into Bypass Mode)? I'm wondering if there is a open link in the command line from the PC to the Digital board. | |||||
| Steps to prolong the life of your OhmMapper system | 4 Relevance | 2 years ago | Gretchen Schmauder | Hardware | |
| The dipole cables are a high failure item as they are subjected to considerable wear and tear. Here are some steps that you can take to prolong the life of the system: Never lift the transmitter or receiver by the pulling on the Dipole cables. While setting up the system, it is extremely important to remember that the transmitter and receiver can easily slip out of the White neoprene covers if you are not paying attention. This will cause them to hit the ground and break the yellow connector, or at the very least jam foreign debris into the connector. A good habit to get into is to carry the units with the nose (cone shape) pointed down, that way they cannot slip out of the neoprene cover. Do not put undue stress by pulling on the system at angles greater than 45 degrees at any given point in the array. Always make broad turns or pick up the array to start a new line. Make sure that the transmitter and receiver are always facing the direction of travel. (The cone pointing towards the console/operator) This will eliminate the possibility of turning the array into a "plow" and placing excessive strains on the connectors, not to mention communication problems. By following these instructions you will find that the instrument's connectors will be able to withstand the strain incurred during normal usage. Of course there may be circumstances that make this difficult, but it is good to be aware of these issues. | |||||
| Battery percentage and status | 4 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 Fluid can I use in my Geometrics Proton Precession Magnetometer? | 4 Relevance | 3 years ago | Gretchen Schmauder | Hardware | |
| List of approved fluids is as follows: n-Decane Shell Sol-71 (Shell oil product) Isopar-G (Exxon oil Co.) Odorless mineral sprits (Naptha) Mineral Spirits (Naptha) Charcoal Lighter Fluid Kerosene lamp oil Kerosene Mineral Oil (medicinal Grade) Diesel Fuel (may degrade diaphragm on marine systems) Camp Stove fuel White Gas Unleaded gas The preferred fluids are items 1-7 above. Items 3 & 4 are not the same as paint thinner. Paint thinner will damage the sensor coils, as will Acetone, and should not be used. Items 11 - 13 have a very low flash point and should be used with extra caution, although any petroleum product must be handled carefully. There are several Alcohols which will produce an acceptable signal, but will tend to absorb water. This will degrade the performance of the sensor over time. These should be replaced as soon as possible with an alternate fluid from the above list. Usable alcohols: Ethanol (Grain Alcohol) at least 190 proof Methanol (wood alcohol) Denatured Alcohol (ethanol made poisonous) All of these fluids must be as clean as possible to ensure that no water or contaminates (rust) are in them. Use a filter to make sure the fluids do not contain rust from the storage container. | |||||
