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| # | Post Title | Result Info | Date | User | Forum |
| Basic Troubleshooting Techniques for OhmMapper | 8 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. | |||||
| What is the MagArrow GPS accuracy in position/elevation/altitude? | 5 Relevance | 2 years ago | Rui Zhang | Hardware | |
| The 3 Meter accuracy of the GPS in the MagArrow I is 50% Circular Error Probable (50% CEP). That means that if accumulating location data at a fixed point for a long period of time 50 percent of the readings will be within a circle with a 3 Meter radius of the actual location, and 50% will be outside that circle. It also requires the GPS antenna have a clear view of the sky with no multipath interference. A good measure of GPS accuracy is to look at the HDOP number. It should be less than 1. Altitude values as a rule of thumb will be half as accurate due to the geometry of satellites. It will be much less accurate if the satellites towards the horizon are blocked, which is often the case. In other words the best accuracy for altitude requires a wide view of the sky. MagArrow II has much improved GPS specs: 50% CEP 1.5m; less than 1m with SBAS. | |||||
| Finding lost MagArrow II with a new MagArrow II | 3 Relevance | 3 months ago | Muhammad Devandra | Hardware | |
| Hello everyone, my name is Devan, and I would like to open a discussion about finding a lost MagArrow. To give you some background, I lost my MagArrow II while it was mounted below the DJI M400 during a flight mission in a highly dense forest. We have the drone flight log, which indicates that it was stuck in a tree within a 50 m radius of the last known location. We have searched the whole area, but due to a highly dense forest and steep terrain, it was very difficult to find the MagArrow II and the drone on foot. For more than a month, I presume it was still perched within the tree canopy. And now we have bought a new MagArrow II to continue our survey. In this case, I desperately want to find and retrieve the lost MagArrow using the new device. I have an idea that if I conduct a 5 m spacing grid in both East-West and North-South directions within a 100-meter radius of the last known location, we could eventually narrow down our perimeter by finding an anomaly that indicates the lost device. Therefore, I have a few questions:1. How magnetic is the drone and the MagArrow II?2. Is it feasible to find the old MagArrow with the new MagArrow with the stated method? Alternatively, do you have any effective suggestions for a different approach? I appreciate any insights you can provide. Thank you! | |||||
| Baseball Caps Create Magnetic Anomalies | 3 Relevance | 2 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. | |||||
| Why does the Signal Strength Vary with the Magnetic Field in High Gradient Locations? | 3 Relevance | 2 years ago | Gretchen Schmauder | General Magnetometer Info | |
| If the sensor is in a very large gradient field such as inside a building near some steel objects, then the high gradients (change of field with distance) causes different parts of the internal sensor components to respond to different fields, making the sum signal smaller. This only takes place when the gradients are very large such as several thousand nT per Meter and will not be seen under normal survey conditions. | |||||
| What is degaussing? How can I degauss metallic components for my magnetometer setup? | 3 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. | |||||
| I'm having trouble triggering my seismograph | 3 Relevance | 2 years ago | Gretchen Schmauder | General Seismograph Info | |
| Geometrics seismographs are designed to trigger on a contact closure, contact open, or signal input. The trigger circuit has protect from high voltages, but it is possible to damage the input circuit if voltages outside the specified range are connected directly to the input circuit. It is recommended that input signals, or voltages do not exceed + 10 volts. A typical voltage measurement using a hand held volt Meter on pins A (+) and B (-) of the 3 pin trigger input connector will be 4.9 volts DC. Voltages less than 4.0 volts may indicate a problem with the trigger circuitry. Often times the unit will continue to operate and trigger, but should be serviced at the next opportunity. If the circuit has been damaged, typical problems will include false triggers, or failure to trigger. To verify the trigger function of the Seismograph, begin by removing the external connector from the trigger input, and short pins "A" and "B" together on the trigger input connector of the seismograph. The unit should trigger each time the pins touched as long as the interval between triggers is greater than the record time or the trigger hold off whichever is longer. It should not trigger unless these pins are touched. If consistent triggering is achieved using this method, then attach the hammer switch directly to the seismograph. Do not put the hammer switch on a hammer yet. Tap the hammer switch cylinder on the edge of a table or other hard object and verify consistent triggering. Watch the stack count on the screen to confirm each tap of the hammer switch results in a trigger of seismograph. Check the trigger hold off setting and trigger sensitivity settings. Set the trigger hold off to 0.5 sec. and the trigger sensitivity to 50. If the seismograph is triggering correctly, insert any trigger extension cables between the hammer switch and the seismograph. Repeat the test to confirm consistent triggering. Then attach the hammer switch to the hammer, or other device used for triggering. Make sure the cylinder of the hammer switch is firmly taped to the handle, and the direction of motion is across the diameter of the cylinder. You can also attach a geophone or other signal producing devise at this point and verify proper triggering. If the unit does not properly trigger, contact support with the results of the tests above for assistance. | |||||
