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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

Stacking waveform data (SEG2) files using Pickwin Make sure your dimension size is large enough. To start, select "option", then "Dimension size". If the maximum traces is smaller than the Total number of traces, increase the maximum traces, check “Change dimension size” and click “OK” to change dimension size. Open one waveform file as usual. Open another waveform file as usual. Choose “Append to present data”. If you want to change the color of traces depending on files, change component (2 to 10), check “Change” and click “OK”. Note that color does not affect stacking. Trace color is shown below. If you uncheck the “Change”, all traces are shown black. Confirm Total number of traces. Two waveform files are shown together. Make sure there is no time difference between shots. After importing 3rd file. After importing 4th file. Make sure there is no time difference among shots. Confirm Total number of traces.. All waveform files are shown together. Make sure there is no time difference among shots. Select “Processing”, “Vertical stack”. Select “a. Average” and click “OK”. You may select “Semblance” or “Semblance weighted stack” to emphasize coherent signal. Stacked data is shown.

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.

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

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.

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.

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.

Thank you for detailed answer. I understood that common practice is separate grounding of each module. Also we will definitely try to shield each geophone with a separate ground, but this will require a large amount of preliminary work. Regarding 50 Hz filtering. We conducted a small experiment in the field to determine the frequencies of background electrical noise captured by geophones. Having Set the minimum possible sampling period for Geod, I recorded 9 consecutive intervals (128 seconds each) of passive observations. This resulted in a Total of 19.2 minutes of continuous background noise recording at 125 Hz sampling rate. Then I calculated the signal spectrum from each geophone separately (19.2 minutes of recording), and then obtained the average spectrum for all sensors. For example, the figure in the appendix shows the average spectrum from 24 sensors (red curve) versus the spectrum of an individual geophone (blue curve). In general, I am interested in noise in the 30-50 Hz range. There are no clear peaks at 50 Hz on the frequency response graph. Peaks at 20, 25, 30 Hz are present constantly at any time of the day. In general, the frequency response of passive observation signals increases smoothly with a maximum around 48 Hz. I mean that filtering in some narrow frequency range in this case will not help much in my understanding. Thanks again for the advice. We’ll experiment. Attachment : 24 geophones 19.2 minutes 125 Hz sample rate.jpg

The cables between the sensors and the MFAM module are flexible circuit boards, and the length is limited to 20 inches. It is possible to remove the MFAM module from the Development kit box and then reconnect it using a ribbon cable. That would allow you to extend the MFAM module and sensors away from the Dev Kit box. Our engineers have tested it to 4 meters. Below are some details about the ribbon cable. The connector on the MFAM unit is Samtec FSH-110-04-F-DH. Its mating connector is Samtec SFMH-110-02-L-D-WT. The easiest option for an extender cable between the MFAM and the Dev Kit is a pair of cable assemblies from Samtec www.samtec.com which has male/female mass terminate connectors put onto a ribbon cable.  These connectors plug directly into the MFAM I/O connector and also into the Development Kit.  We are comfortable with lengths to 10 feet Total.  The samtec P/N for this cable is:  FFMD-10-T-60.00-01-F-N The ‘60.00’ number specifies the cable length in inches (which equals 5 feet).  We have found that there is generally a 2-4 week lead, time since they are made to order and not an off-the-shelf part. (There is another solution as well if you want to make adapter boards at each end (Dev Kit and MFAM).  The exact Samtec mates for the MFAM / Dev Kit connectors are made in PCB mount connectors only, so if you make simple small adapter board to adapt the samtec connector to another connector of your choice.  We've done this with ExpressPCB which is fast and inexpensive.  A board Set from ExpressPCB is about $70 including shipping.  Our Engineering Team has a design and parts list they can send you if you're interested in going this route.)

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).

It is a fairly simple task to connect a GPS to a G-858 magnetometer. You can use the External I/O cable assembly and a null modem to connect the G-858 to most GPS receivers. Null modems are available from Geometrics or from local Radio Shack or computer stores. The Null modem pin configuration for GPS receivers that have a data cable compatible with 9 pin IBM PC COM ports has male pins on both sides. The GPS should be Set to output NMEA data that contains the $GPGGA sentence. Be sure to Set the RS232 protocol to 9600 Baud, 8 Databits, 1 Stop Bit and No Parity. The G-858 must have its serial port Set to the same baud rate as the GPS. You can use System Setup -> Com & Field Note String Setup -> Chat Mode to determine whether correct communications have been established.

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).

MagStation, the new MFAM magnetometer base station is available. It's Geometrics’ latest and most advanced magnetometer base station, designed for high-sensitivity, stationary monitoring of the Earth’s Total magnetic field. Please see the product page for details. MagStation Magnetometer Base Station