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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.

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.

Further Elaboration: You might ask this question to try and understand the low frequency response to determine if the Geode amplifiers effectively have a flat response from DC up. Does the Geode go down to DC for example? Answer: We apply anti-alias filters to the data to prevent out of band noise from being introduced into the data. The filters are Set with a corner frequency at ¾ of the Nyquist frequency (1/2 the sampling frequency) for almost all of the sampling frequencies. When we sample at 1.5625 uS, the Nyquist frequency is 32kHz and the filters are Set at 20 kHz, because of limitations of our electronics. There are two single-pole filters: one analog and one digital. The analog filter is a simple RC filter with 1uF +/-5% and 100kOhm +/- 1%. We short out the capacitor in the conversion process. The digital filter is software controlled when the option is registered, so it can be switched in or out in the field. It is an IIR Butterworth with a -3dB corner at 0.9Hz for 48ksps sampling, and 0.6Hz at all the lower sample rates. Also, we offer software and hardware options to modify the low end frequency response of the Geode. Low-end bandwidth modification: 1.5 Hz, P/N 28311-37 0.6 Hz, P/N 28147-01 DC, P/Ns 28147-02, 28311-37per system plus

MFAM-SuperMag (LCS100S) or MFAM-SX (LCS100X) can be configured to achieve dead-zone-free operation, in which the combined sensor is always active no matter where in the world and which direction the device is oriented. To Set up the dead-zone-free configuration: Make sure the MFAM is in the "One Sensor (No Dead Zone) run mode. If not, please refer to "How to switch the operating mode for SuperMag MFAM" on our website found here: How to switch the operating mode for SuperMag (LCS100S) MFAM?. Orient two sensors orthogonally. The ideal relative orientation is shown below (also in the test report in the USB drive shipped with the unit). This configuration works for both the "Low Heading Error" and the "Low Noise" modes. Low Heading Error Only mode If you only wish to run the sensor in the "Low Heading Error" mode (note that SX MFAM does NOT have the "Low Noise" mode), a simpler configuration, as shown below, can also achieve the dead-zone-free operation.

To Set the time on a MetalMapperII Panasonic Toughpad tablet: 1) Using the Applications menu, open a terminal window 2) Set the date and time you want, using the following example as a guide: sudo date -s "2024-02-20 03:25:55 PM PDT" You may need to enter the sudo password (which is the same as the password for the standard "geometrics" user. 3) To change the timezone, use the terminal window to get a list of timezones: ls /usr/share/zoneinfo // To drill into a region, expand the command as follows: ls /usr/share/zoneinfo/Pacific Set the local timezone using this command: // Open the timezone file to edit it. You may need to enter your user password sudo mousepad /etc/timezone // Type in the timezone name, of the timezone you want to use, on a single line in the file, for example like this: Pacific/Guam If you want to see your time in UTC, Set the timezone to "Etc/UTC". If you want to Set the time in UTC, then when you Set the time using the "date" command, use UTC as follows: sudo date -s "2024-02-20 03:25:55 PM UTC"

The time associated with each data point in a SEG-2 data file generated by a Geode is related to the time of the “trigger” event which was instrumental in the production of the file and its content. The Trigger Master and Trigger distribution The trigger event occurs at the Geode designated within the Controller software as the Trigger Master. Although all Geodes are capable of being Trigger Masters, there must be one and only one Trigger Master in any properly functioning Geode system. The Controller automatically takes care of this requirement when the designation is made by a user, and when the system is established at the time of Controller start-up based on a previous designation (or a default Setting in the case of a “new survey”). All other Geodes in the system will have their Trigger Master circuit disabled. A trigger event can be initiated by an external electrical pulse provided to the trigger input connector of the Trigger Master Geode, or by a command sent via Ethernet from the Controller to the Trigger Master (usually for test purposes), but only when all conditions are satisfied to allow data recording. There is also a special trigger initiation situation, called “self-triggering” which will not be discussed further here. Upon acceptance of a trigger event, the Trigger Master will distribute the trigger signal to all Geodes in the system, itself included, via an RS-485 network that resides within the digital interconnect cabling. (Proper termination of this RS-485 network is automatically taken care of by the Controller.) The trigger signal is propagated through the cabling and Geodes at the nominal speed of 70% of the speed of light, or approximately 2.1x10^8 m/sec. The maximum distance of successful propagation depends on a number of factors such as the number of Geodes involved, the noise environment, the quality of the cables, and the acceptable amount of timing uncertainty for the particular application. distances approaching or exceeding 1km should be given careful attention in this regard. In a 3-D Geode system involving LTUs, each LTU, unlike a Geode, will reconstruct the trigger signal before sending it on, effectively confining the maximum distance issue to each sub-network separated by LTUs. The penalty is an additional delay of about 100nS for each LTU in the route. The External Trigger Circuit The external 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 will trigger (if enabled) if and when the coupled signal exceeds the window, in either direction (i.e., positive or negative going). 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. Sub-sample Synchronization The Geode supports a sub-sample timing synchronization feature used for synchronizing the data acquisition after a trigger event to the distributed trigger signal, so that subsequent time points will be known to within 1/32 (~1/20 at the fastest two sampling rates) sample interval. It does this by increasing the sample interval at the trigger time by 0 to 31/32 of a sample interval in increments of 1/32, so that the first sample after the trigger would represent a time of one sample interval after the trigger event, with a tolerance within 1/32 of a sample interval. The following samples continue from there at the expected intervals. For example, with a selected sampling interval of ¼ mS and a recording delay of 0mS, the first sample in the recorded file for each channel would represent data at 250 to 258uS after the trigger event. This of course potentially introduces a small discontinuity at the time of the trigger, observable depending on the nature of the channel waveform(s). (The zero-phase anti-alias filter will smear the discontinuity into the nearby samples both before and after, consistent with the bandwidth of the filter.) Sub-sample synchronization can be disabled if it is deemed to be detrimental for the particular application, at the expense of losing the 1/32 interval timing accuracy. Timing Errors The principal errors in Geode timing are of two types: those associated with the trigger mechanism and which are static over the duration of the record, and those associated with the time base and which change over the duration of the record. Excluding the trigger propagation delay mentioned above, the trigger timing uncertainty is about 1uS. The known fixed errors have been lumped together and are reported in the SEG-2 file trace headers as channel SKEW. (The actual channel skew is zero, since all channels are effectively sampled simultaneously, but the SKEW value in the header is used as the only place permitting small timing corrections. Note that the SKEW value for every channel is identical.) If the size of this correction is important to the application, the SKEW value should be added to the calculated time points when the data is being processed. The Geode time base has a +/-15ppm stability over temperature (-20C to +70C) and component variations. Thus time drift relative to absolute time and relative to other Geodes is possible. (However, all channels within any Geode enclosure use the same time base, so there is no relative drift between channels in the same enclosure.) Therefore timing uncertainty increases from that existing at the time of the trigger until the time of the next trigger (or end of record). Special Timing Issues Involved with “Continuous” Recording “Continuous” recording is a method that allows unending 100% time coverage with recorded Geode data. It produces a series of time-overlapped records created by the use of a negative time delay Set equal to the record length such that each record consists of completed history at the time of the trigger event. This technique circumvents the problem of data transmission overrunning data acquisition. The principle constraint is that the cycle time from trigger to trigger must always be less than the chosen record length. Otherwise, gaps rather than overlap would result. Commonly it is used with GPSderived triggering in order to provide time-stamping of each trigger event. Upon consideration of the above, it will become clear that the time-stamp associated with a particular trigger event will pertain to the data in the following record, not to the data in the record in which the time-stamp is written. This comes about because the trigger event ends the record. Because there is data overlap between records, the precise trigger point in the following record at which the time-stamp applies can be found by comparison of the data values at the end of the former record with those near the beginning of the subsequent record. The overlapping data will be exactly identical in both records (since they are read from the same memory location, twice). The earliest data in the subsequent record that goes beyond the data of the previous record is the data that is one sample interval (assuming sub-sample synchronization is enabled) past the time-stamp. Note well that this comparison must be made independently for at least one channel of each 8-channel Geode board Set, because the discrete time at which data values are written to the memory buffer, relative to the trigger event, is a function of each individual board Set in the Geode system. Correct GPS Time-Stamping There are differences between various GPS models that can affect accurate time stamping. The 1PPS signal from a GPS has a “timing edge” and return edge, of which only the former is the true whole-second edge. Some models use a rising edge as the timing edge, some the falling edge, and some have it selectable. Consult the GPS manual to determine the definition of its timing edge. As indicated earlier, the Geode can be triggered on either a rising or falling edge. It is important to insure that the Geode is being triggered on the proper edge in order to avoid timing that may be a fraction of a second off. This is expanded upon below. Some GPS units provide a very narrow timing pulse, others one that has a nearly 50/50 duty cycle. For the narrow pulse units, almost certainly it is the leading edge (rising or falling) that is the “timing edge”. This case can be easily handled by using the Geode Trigger Hold-off feature. If a 10-second cycle time is desired, Set the Trigger Hold-off time to about 9.5 seconds. In this case, there is a very small chance that the very first trigger could occur on the wrong (trailing) edge, but from then on the leading edge will be used as the triggering edge. If the GPS provides a 50/50 duty cycle edge, and it is not alterable, then the Geode by itself could as easily start on the wrong edge as on the correct timing edge, and continue thusly until restarted. For this case, Geometrics can provide a Trigger Timing Interface Box (TTIB) that will correct the situation. The TTIB can be programmed to respond only to the correct edge (rising or falling), change the polarity if needed, and gate through only one of every N 1PPS pulses, where N is programmable. (The TTIB also incorporates an alarm system that can provide a remote alert if a record is missed.) Another potential issue comes from the variations between GPS models of the time that the serial time string (containing the time value of the associated 1PPS) is issued relative to the 1PPS itself. The Geode Controller attempts to pick the correct serial string based on a calculation involving the known record length, the PC times, and the trigger notification message from the Geodes. But if the GPS issues the serial string at an unusual time (and the time has been seen to vary somewhat with a given GPS unit) then it could pick up the incorrect time, off by 1 second. If rare, it can be subsequently detected and corrected during data processing, but if consistent it may not be easily detected. Again, the TTIB can accommodate the situation by only gating through to the Controller PC the string belonging to the gated-through 1PPS pulse. The Controller Serial Input Time Window can then safely be widened to 2 seconds (assuming the cycle time is more than 2 seconds) if need be, to expand the Controller’s search for the string around the calculated trigger time.

If you purchase a low-noise MagArrow (I or II), the factory default is the low-noise mode. You can also look up the current running mode by loading the following website (in Instrument Status) after connecting to the MagArrow: 192.168.1.1/systemtest.cgi To switch to a different mode, please download the special software below and follow the instructions in the readme file: Attachment : SwitchModes.zip Please note that even in the low-noise mode, the heading effect is typically only ~20% worse than that in the low-heading mode. For most applications, you don't need to switch to the low-heading mode.

You can 3D print a dead-zone-free sensor holder from the attached .step file. Attachment : Sensor Holder Perm Shell_Thin Wall_v10.zip

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.

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!

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.

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.

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.

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.

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).