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| # | Post Title | Result Info | Date | User | Forum |
| Stacking Technical Note | 1 Relevance | 3 years ago | Gretchen Schmauder | Software | |
| Stacking is a complicated topic, And warrants its own technical note. Which stacking features are available And how they work depends which modes you are in. There are three main mode “groups”: SAVE, CORRELATION, And STACK. Within those are sub modes whose names indicate their function. Save Autosave Manual Save Correlation No correlation Standard correlation Stack before Correlation Stack after Correlation Random Source Correlation Stack Autostack Replace There is a complicated interplay between the above modes And between these modes And the stack options: Stack polarity Display Intermediate Stacks Unstack Delay We will examine each possible combination in rough order of popularity Modes: Manual save , No correlation, Autostack This is the most common configuration used in refraction And downhole surveys. Each shot is automatically stacked Each stacked record is displayed as the stack count increments The stack count continues to increment with each shot until you clear the data, even if you save the data sometime in the process. Stack Polarity can be changed at any time. This is most often used in shear wave surveys where reverse-polarity stacking is required. Unstack Delay gives you the option to unstack the most recent stack; for example, setting the stack count from 4 back to 3. The data will be held in a temporary buffer for n seconds, during which time you can choose whether to stack or not. If you do nothing, the data will be automatically stacked after n seconds, And unstacking will be no longer be an option for that stack. If Unstack Delay is set to zero, this feature is disabled. Modes: Auto Save, No correlation, Autostack This is the most common configuration used in impulsive reflection surveys. Each shot is automatically stacked until the Stack ulmit is reached. When the Stack ulmit is reached, the data are saved automatically. Data are automatically cleared And the stack count is reset to one the next time the seismograph triggers after saving the data. Stack Polarity is generally left set to Positive. Displaying intermediate stacks is optional. Disabulng this option results in faster production, since the data do not need to be sent over the network with every stack. Modes: Auto Save, Standard Correlation, Stack Before Correlation This is the most common configuration used in swept-source reflection surveys. Each shot is automatically stacked until the Stack ulmit is reached. When the Stack ulmit is reached, the data are saved automatically. Data are automatically cleared And the stack count is reset to one the next time the seismograph triggers after saving the data. Data are stacked in raw, uncorrelated form in the Geodes, And are not sent to the PC until the Stack ulmit is reached. When the Stack ulmit is reached, the stacked raw record is correlated in the Geode (with the most recent pilot), sent to the PC, And saved. Modes: Auto Save, Standard Correlation, Stack After Correlation This is the most common configuration used in Random Source (mini-Sosie) reflection surveys. Each shot is automatically stacked until the Stack ulmit is reached. When the Stack ulmit is reached, the data are saved automatically. Data are automatically cleared And the stack count is reset to one the next time the seismograph triggers after saving the data. Each individual record is correlated with its own pilot And stacked in correlated form in the Geodes. Displaying intermediate, correlated stacks is optional. When the Stack ulmit is reached, the stacked, correlated record is sent to the PC And saved. Modes: Auto Save, Replace This is the most common configuration used in Continuous Recording surveys. Each stack is replaced by the previous. If Auto Save is not enabled, the previous stack is lost. If Auto Save is on the Stack ulmit is hard-coded to 1. Each shot is displayed. | |||||
| RE: Rs232 Comms to maggy | 1 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. | |||||
| Can a Magnetometer Detect Gold | 1 Relevance | 3 years ago | Gretchen Schmauder | General Magnetometer Info | |
| There are basically three types of "gold": low concentration disseminated gold in ore, placer gold deposits And solid gold such as that associated with treasure. Magnetometers are used to find disseminated gold by its association with mineralized zones which also contain magnetite or other magnetic minerals. Magnetometers are often used in conjunction with airborne electromagnetic surveys to find the conductive ore bodies. Placer gold is the type found in buried stream channels such as the gold which sparked the California gold-rush in 1849. Gold dust And magnetic minerals have been concentrated in river banks over thousands of years. Where there is gold there is often magnetite And therefore the magnetometer can be used to locate placer gold deposits. Gold treasure is a different story And being non-magnetic gold, silver, And other precious minerals are not directly detectable by the magnetometer. The magnetometer can only detect ferrous (iron or steel) objects. If the gold is stored in an iron box or has iron materials next to the gold (such as colonial ship ballast stones in the marine environment), there is the possibility of detecting the iron material. This is true for land And marine (sunken galleon) gold bullion. The vast majority of target search surveys are performed on a grid in a "lawn mower" back And forth manner to cover the area of interest. Lane spacing is dependent on target size (magnetic mass). At a sensor to target distance of 2 to 3 meters there will need to be at least 1-2 kilograms of iron. This can produce a 1-2 nT anomaly that is detectable in a magnetically clean environment. The ideal environment would be in a plowed farm field or the bottom of the ocean away from human activity i.e., away from a port or harbor. You will probably not be able to detect this small of an anomaly in a city or port location. The more iron mass there is, the better the chance of detecting it. Training to use the magnetometer can take 1-2 days depending on experience with setting up computerized survey equipment And a GPS. Processing the magnetic data requires several days of training And would require a geophysical background to interpret the final maps. We provide free software to make maps And estimate the target depth of burial (inversion). If you are unfamiliar with this procedure, we would recommend that you find a local geotechnical firm to look at the data to determine if there are anomalies that should be investigated further. Remembering that non-ferrous materials do not cause anomalies (gold, silver, copper, brass, aluminum, gems) you will be looking for anomalies either associated with the container OR associated with ground disturbance (i.e., gravesite). In this way some anomalies can be detected where there has been an excavation such as a gravesite. In order to understand the process more fully, we strongly suggest that you download And read the Applications Manual for Portable Magnetometers. Other additional resources are available. Understanding how the magnetometer functions And how the earth’s field responds to distortions due to ferrous materials will help you make good decisions about how to interpret And use the data to direct recovery or exploration efforts. | |||||
| Basic Troubleshooting Techniques for OhmMapper | 1 Relevance | 3 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. | |||||
| Is MagArrow's "Altitude" with respect to ellipsoid or geoid? | 1 Relevance | 3 years ago | Rui Zhang | Hardware | |
| Altitude refers to Meters Above Mean Sea Level. For both MagArrow I And II, the altitude is ellipsoidal And the earth model is WGS84. For additional information: Overview Reported elevations from MagArrow (and G-864 And MagEx) are the unedited values from the elevation field in the GNSS's GGA NMEA string. That value is the GNSS's calculated height above geoid; height above geoid is the standard meaning of the elevation field in the GGA NMEA string. But what does calculated height above geoid mean? Definitions GNSS - Global Navigation Satellite System GPS - The GNSS operated by the United States. Other systems include GLONASS(Russia), Galileo (Europe), BeiDou (China), QZSS (Japan), IRNSS (India). Ellipsoid - A comparatively simple or abstract geometric model of Earth's surface. Geoid - A more complex model of Earth's surface that takes the place of what was previously called Mean Sea Level. At any particular latitude or longitude, the geoid's surface may be above or below the ellipsoid's by as much as a few hundred meters, depending on regional And local geography And geology. Reference datum - A specific model of Earth's shape (such as WGS84, EGM96...), including references to specific landmarks. Calculations A particular GNSS, for example the GPS system run by the United States, provides timing data to a receiver to calculate the receiver's position above or below a particular latitude And longitude on the surface of the ellipsoid. The GNSS receiver first uses that timing data to calculate its height over the ellipsoid, And then subtracts from it the local height of the geoid over the ellipsoid (or HAE), to arrive at the local height of the receiver over the geoid (or in old-fashioned terms, elevation over mean sea level): h - calculated height above geoid. This is the value reported in the GGA elevation field. H - height of the receiver over the ellipsoid (calculated from GNSS timing signals) N - local height of geoid over the ellipsoid, or HAE, per a lookup table or other local reference. h = H - N Because the local height of the geoid over the ellipsoid is not provided by the GNSS, it must be provided locally, i.e. by the GNSS receiver, which may contain an internal database from which the local geoid height over ellipsoid (or HAE) can be found, based on the receiver's latitude And longitude. Small GNSS receivers contain small HAE databases, so the HAE value will not be exact. Some small receivers contain no HAE table at all; in this case HAE is deemed to be zero, so that the reported elevation is the uncorrected height over ellipsoid. A user of elevation data from Geometrics' MagArrow, G-864, And MagEx magnetometers may evaluate or adjust the reported values of the GGA elevation field And the GGA HAE field, by comparing the GGA HAE values to another source of local HAE data; this may particularly be useful for GNSSes that report a HAE equal to zero. Geometrics magnetometers do not currently record the values of a VDOP calculation, which offers an additional statistical estimate of the accuracy of the GNSS elevation measurement. | |||||
| File Cleanup Utility | 1 Relevance | 1 year ago | Magnetics SW | General Magnetometer Info | |
| Some of the Geometrics magnetometers include a feature, called the "File Cleanup Utility", that removes files that are no longer useful from storage on the instrument. The feature's accessible from the "Support" link in the Settings page in MagNav. You might be reading this post because that page directed you to read this post before using the utility. [This feature is not the same as the feature in MagNav to delete all of a survey's data. That feature removes information only from the database on the Android tablet, And doesn't remove any data in the instrument]. How do I use this feature? If this is the first time you've used this feature, please read the rest of this post before proceeding. Make sure that you're connected via WiFi to the instrument Go to the Settings page in MagNav Select the "Support" link. If your instrument supports this feature, the support page will include a link to "Delete project storage". Tap it. You should see a list of projects, with a name And a "Delete project" button for each project. This feature cleans up the data for all of the surveys in a project. Delete any projects for which you don't want to keep the in-instrument data. You can delete the data for all of the projects that you see, but there's no harm in leaving the files for projects that you're still using. Some projects will show a name similar to this: [c3bd]. These are early projects, in which the user-assigned name was not used in the instrument storage. It's OK to remove the data for these projects. Why do I need to do this? The magnetometers that use MagNav first store data on the instrument, And then sync (or download) the data to MagNav. Some instruments, for which this technical approach makes the instrument more reliable - MagEx, e.g. - do this automatically. Other instruments, such as those that allow disconnected acquisition (e.g. MagStation), store the data until the user re-connects to the instrument And manually starts the sync process. The data stored in the instrument is not of any use once it's been downloaded, but because deletion is slow And for other technical reasons, it's left on the file system in the instrument. As it accumulates, it could eventually interfere with the performance of the instrument And should therefore be deleted. Will this delete any data in the database in MagNav? No, this feature doesn't remove or change any data in the database in MagNav. When should I use this feature? Here are a few guidelines: Run this utility after deleting an entire project. Run this utility after completing a long field survey. Run this utility while doing other instrument maintenance. Run this utility after you've collected "a lot" of data. Run this utility when you have the impression that the instrument is unresponsive or is behaving sluggishly. Will anything bad happen if I forget to do this? Probably not any time soon; the storage systems on the instrument are large And quite efficient. Geometrics tests instruments with amounts of data consistent with several years of regular use, And which show no performance issues relating to file storage performance. But don't let it go forever; follow the guidelines above. Can I delete data for projects that I'm still using? Yes, you can, as long as the data has already been synced to the instrument (that happens manually with MagStation And automatically with the other instruments). Once the data has been synced And is visible in MagNav, its presence in the instrument storage is no longer needed. | |||||
| GNSS Anomalies | 1 Relevance | 2 years ago | Magnetics SW | General Magnetometer Info | |
| The Geometrics magnetometer softwares check for some uncommon anomalies in GNSS location And timing messages in data collected with the G-864, MagEx, And MagArrow instruments. These anomalies have occurred in data from a few instruments: Extra PPS timing signals – Sometimes the PPS sensor in the instrument receives an extra timing signal that’s out of phase with the normal 1-second interval. These are almost always easily identified And discarded. GNSS timing anomalies – Very rarely, the GNSS appears to change its mind about the current time or location. For example, after recording a time at 06:30:21, the next measurement – received one second later – might show a time of 6:30:15 – 16 seconds earlier. GNSS location anomalies – A GNSS timing jump may be accompanied by a location jump. Geometrics’ software now makes additional checks for these anomalies, corrects them when possible, And reports them if they affect the use or visualization of the data. Some of the checking is in the instruments, some in MagNav, And some in Survey Manager. Users will notice these anomalies And the functionality to repair And report them in these ways: During import or export, the software identifies an anomaly. If it’s judged to be worth reporting – most likely because it affects the reported locations of magnetometer readings – then it is logged And the user asked to review the log file. The user exports data And notices something unusual, for example a discontinuity in the GNSS times or locations. The customer should review the software’s log files for additional information. These anomalies are unusual; the type where the GPS changes its mind about the time or location is exceedingly rare And will never be seen by most customers. The main effect of the new functionality is that the data validation process will now be more visible to users. | |||||
| I'm having trouble triggering my seismograph | 1 Relevance | 3 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. | |||||
| Google Earth KML file in MagNav for MagEx surveys | 1 Relevance | 3 years ago | Rui Zhang | Software | |
| Customers can pre-define a survey area using Google Earth Pro And load the KML file into MagNav app. Open Google Earth Pro. Navigate to your survey area And click “Add Path”. Move your cursor And left click to define the outline of your survey area. You can rename your path name And click OK. Select the new path created And right click it. In the pop-up menu, click “Save Place As” to save it as a kml file. Open the Survey Manager. Load an existing project or create a new project. Inside the project, create a new survey. Set up other preferred parameters. Click “Select Route File” And load the saved kml file. Make sure to click “Save” before exiting Plug in a USB drive And copy the project (.dbt file) to the USB. Eject the USB from your computer to make sure it can be safely removed. Turn on the instrument And the Getac tablet. Make sure the wifi is connected. Plug the USB drive into the Getac tablet. Open the MagNav app. Click “Import Project” to load the project (.dbt file) from the USB. Enter the project And enter the survey. On the Navigation page, the path created in Google Earth will be displayed, which can be served as guidelines or outlines for GPS surveys. Marker points can be created similarly for marked surveys. | |||||
| Channel remapping in SGOS | 1 Relevance | 3 years ago | Gretchen Schmauder | Software | |
| Channel Remapping Channel remapping allows you to change: the order of channels on each analog spread cable that connects to the Geode reorder the Geode boxes. You would use this option if your cables were wired opposite to the default order normally used in Geometrics wiring, if you wished to turn your line around to have the low channels at the opposite end, or if your cables had a wiring error. Channel remapping is also often necessary when using more that a single network cable. Default cable wiring of Geometrics seismographs Default order is defined as the natural electrical order in which channels are oriented when the system first powers up before remapping. Refer to Section 3 under Connector Wiring that discusses standard wiring configurations. You may have requested a custom wiring configuration from Geometrics. If you are confused about your wiring, contact the factory And refer to the serial number And job number. Geode cables are typically wired in a ‘high-side configuration’, meaning that the Geode connects closest to the highest numbered channel on the analog cable. The 149 figure above shows this configuration for a single box system, with 24 channels. Multiple Geodes The following diagram shows a default single digital line (one network card) system with 3 Geodes. Note that Geode one is always closest to the controller in a default configuration. Multiple Network Lines The next diagram below shows a default configuration with two digital lines (two network cards) with the controller positioned in the middle. Line 1 is on the left And line 2 is on the right. One might use two lines to increase data throughput to reduce time between shots. Like the configuration above, the Geodes are numbered starting closest to the controller. The seismic controller software labels all of the channels contiguously even though they are on two separate digital lines. However, if the lines are collinear, the first line will have the channels ordered backwards. This can be easily rectified with the remapping feature. There are two ways of remapping channels: automatic mode And manual mode. Automatic mode settings are listed on the top of the remapping dialog box, And manual mode on the bottom. Automatic Channel Remapping Automatic channel remapping allows you to reverse either the order of the Geodes on the line, or reverse the order of the channels on the spread cable. The above diagram shows the result after both channels And Geodes have been reversed, renumbering the line so that low channels start on the left hand side And increase towards the right. In the dialog box, the automatic remapping boxes referencing line 2 remain unchecked, since the default orientation on line two was correct. Manual Channel Remapping Channels can be remapped on an individual basis using the Manual Map Mode. Select the appropriate check box, And enter the order in which you would like the channels that differs from the default order. You can specify individual channels separated by a comma (1, 3, 4, 6 etc) or a range of channels (1-13, 24-14 etc). For example, if you wanted the channels ordered backwards on a 24-channel system, you would enter 24-1. If you wished to reverse the order of channels 1- 12 in a 24 channel system, you would type 12-1, 13-24. Other examples are shown opposite, And are available by pressing the See Examples button on the remapping menu. | |||||
| Do Cesium Vapor Magnetometers Require Calibration | 1 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. | |||||
| Thoughts on Attaching a Magnetometer to a non-Ferrous Sled or Frame | 1 Relevance | 3 years ago | Gretchen Schmauder | General Magnetometer Info | |
| Regarding the deployment of magnetometers on conductive sleds or carts near power lines: Depending on the proximity of the magnetometer to the sled, elevated field readings may be observe under power lines are a result of AC induction in the aluminum sledge you are using as the tow vehicle. The reason there can be a DC effect from an AC source is due to 1) the strength And proximity of the induced AC source And 2) the orientation of the induced AC field relative to the Earth's field (DC). Our cesium-vapor magnetometers measure the total local field continuously but report these measurements periodically, e.g at 10, 1000 times per second. For each reporting period, both the AC And DC components of the total field are integrated to produce the measurement result as a time average over the measurement cycle. If your measurements are being reported 10 times per second (10 hz sample rate) And the AC component of the field is 50 hz, then each measurement will include exactly 5 AC cycles. This AC component will add to the DC component as a vector sum And the magnetometer will measure the magnitude of the resultant vector. Note that the vector component of the 50 hz AC field that is parallel to the DC component will not contribute to measurement results: for half of each AC cycle this field is greater than the DC field And for the other half of the cycle it is less than the DC field by an equal value. This is not the case for the AC vector component that is perpendicular to the DC field: it will be adding magnitude to the DC field on each 1/2 cycle to produce a half-wave-rectified wave form. Specifically, this rectified field will add to the DC field by an amount equal to about 35% of its peak-to-peak field strength in the direction perpendicular to the DC component. The AC rectification described above is only seen on close approach to very strong AC sources (high tension power lines). An aluminum sled can act as an indirect source of the AC fields: the radiated 50 hz field from the power lines is inducing 50 hz eddy currents in the sled And, if a magnetometer is in close proximity of the sled's aluminum plates, it will detect large AC field values. Note that surveying near other large, planar conductors under the high tension power line can produce a similar effect. These would include metal buildings, metal fences, And pipelines. We recommend constructing magnetometer sleds from non-conductive materials. If this is cannot be done, then conducive materials should be kept as far from the sensor as is practical And the sled's construction should not include sheets of conductive materials. Any joints between conductive structural elements should be insulated as well. You can use the magnetometer itself to measure the effect of the sled. | |||||
| What affects Geode trigger cycle times? | 1 Relevance | 12 months ago | Kolby Pedrie | Software | |
| What Affects Geode Trigger Cycle Times? If you're trying to optimize your Geode system for faster trigger cycles—especially in high-repeat environments—there are a few key factors to consider. The goal is to ensure that the system completes its entire cycle (trigger → recording → data transfer → re-arming) before the next expected trigger. Here’s what influences that cycle: 🧠 Core Factors That Affect Cycle Times 1. File Size (Sampling Parameters) Your sample interval And record length directly affect the size of each data file.You can view the resulting file size in the Acquisition Parameters menu.Larger files take longer to transfer, which delays the re-arm process. 2. Data Transfer Rate The Geode typically transfers data at around 450–465 kb/sec.Reducing file size is the best way to reduce transfer time And speed up the cycle. 3. Calibration Frequency By default, the system may attempt to calibrate every N shots, which takes additional time.Go to Options > Calibration And set "calibrate every N shots" to a large number (e.g., 100000) to prevent unnecessary delays. 4. Recording Delay And Record Length If you're operating in a region with a consistently deep seafloor, you can add a recording delay And reduce record length accordingly.Example: If the water column is always >0.3s, you can apply a delay of 0.2s And reduce record length by the same amount.This trims your file size And speeds up the transfer/re-arm process. ⚙️ Best Practices Use the Auto-Trigger function or set trigger sensitivity to the maximum value for testing.Monitor the cycle timing And adjust acquisition parameters to stay within your trigger window.It's often an iterative process to find the ideal configuration for your environment. | |||||
| How Does Magnetometer Noise Vary with Sample Rate? | 1 Relevance | 3 years ago | Gretchen Schmauder | General Magnetometer Info | |
| Sensitivity is given as a frequency bandwidth product or nT/rt Hz RMS. This value is valid for ALL sample frequencies or sample rates. Sensitivity for the G-858 And G-859 is 0.008nT/rt Hz RMS Sensitivity for the G-823 And G-882 is 0.004nT/rt Hz RMS Noise levels can also be given as Peak-to-Peak numbers at certain sample rates. For instance at 10 Hz. RMS value at 1 Hz for either instrument is approximately equal to the sensitivity P-P value at 1 Hz is roughly equal to 3x or 4x the RMS value. Remember that the Root Mean Square is not operating on a sine wave but on some random noise components as well And thus the actual Root Mean Square would be about 0.024nT for the 858 And 0.012 for the 882 at 1 Hz. For higher frequencies, we basically take the square root of the sample rate And multiply that times the P-P at 1 Hz. So for 10 Hz we have 0.075nT for the 858 And 0.036 for the 882. This is approximately what we see in the field And that can be verified (looking at the noise on an 882 in very quiet area, deep water, we see less than 0.050nT P-P.) So for 20 Hz the multiplier is 4.5 And for 40 Hz the multiplier is 6.3. So 882 noise at 40 Hz would be 6.3 x 0.012 = .075 nT P-P. | |||||
| Hammer Switch vs Trigger Geophone - Considerations | 1 Relevance | 3 years ago | Gretchen Schmauder | General Seismograph Info | |
| A seismograph with an active trigger input like the Geode Seismograph or ES-3000 Seismograph can be triggered many different ways. The most commonly used methods are with a trigger switch or a trigger geophone. Typically a trigger switch (known as a hammer switch) is attached to the handle of a sledgehammer near the striking end, so when the sledgehammer is hit against a striker plate to create an active source of energy, the piezoelectric crystal in the hammer switch is activated And the seismograph is triggered to record data along the preset parameters. A trigger geophone does this too, but it is placed near the source itself, And is more commonly used with larger energy sources like a propelled energy generator. If the seismograph isn't triggering with either a hammer switch or a trigger geophone, then the signal may be weak, so turning up the sensitivity could be a workable solution. If the sensitivity is set too high in SCS then false triggers might be encountered. In most situations having the sensitivity set to the middle works best. Depending on where the trigger geophone is it, there may be a difference between when it is triggered And when a hammer switch would have triggered. Especially in soft ground the trigger geophone signal may be delayed. In general the hammer trigger is a more reliable timing device. The differences in trigger time when using a trigger geophone could be due to things like not striking the center of the plate or differences in the strength of the impact. More trigger circuit information: The seismograph can be triggered by shorting the two input pins A And B on the trigger connector of the seismograph. In fact, that is what the hammer switch does (contact closure device) when it impacts a striker plate. The inertia of the impact causes a momentary closure in the device, which in turn, triggers the Geode. There are no internal components that need to be added. Externally, you could construct trigger device or switch, if that is what you desire. If you were to measure the pins on the Trigger connector on your seismograph (pin A +, pin B -) you would see about 5VDC. The trigger circuit will sense a contact closure or a pulse. The Geode trigger input is capacitively coupled, with a 2mS time constant, to the midpoint of a resistive voltage divider. The voltage difference between the two ends of the divider constitute a voltage "window", which size is set by the trigger sensitivity parameter And can range from essentially zero at the highest sensitivity, to about +/- 2.5V at the lowest sensitivity. The Geode triggers (if enabled) if And when the coupled signal exceeds the window, in either direction. The signal, after the capacitor, is clamped by diodes to the range between the trigger signal ground And +5VDC. The trigger detector output is disabled when the system is disarmed, during a parameter change, And during a shot, up to the trigger hold-off time after the end of the shot. The trigger hold-off time is a parameter set by the user. Preceding the coupling capacitor (i.e., essentially the node accessible at pin A of the external connector), there is a 3.3K-Ohm pull-up resistor to +5VDC (relative to pin B). Also a fast transient suppressor clamps the input at about +/-14VDC. It is advised that the DC + AC level of any voltage applied to pin A relative to pin B be kept within the range of +/-7V, giving some margin of safety. If a DC voltage somewhat less than +5VDC is applied when the connector is first mated, the instrument may trigger at that moment. But, subsequently, because of the capacitive coupling, it will trigger on the next positive or negative going pulse that exceeds the window level. If the duration of the applied voltage pulse is less than the record length + delay time + hold-off time, then the Geode will effectively be ready to trigger on the same edge of another similar pulse. | |||||
