Geometrics G-824A Operation Manual
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Geometrics G-824A Operation Manual

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G-824A CESIUM MAGNETOMETER
Operation Manual
COPYRIGHT © 2014
P/N 27731-OM
Revision A7
GEOMETRICS, INC.
2190 Fortune Drive, San Jose, CA 95131 USA
Phone: (408) 954-0522
Fax: (408) 954-0902
EMAIL:
sales@geometrics.com

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  • Page 1 G-824A CESIUM MAGNETOMETER Operation Manual COPYRIGHT © 2014 P/N 27731-OM Revision A7 GEOMETRICS, INC. 2190 Fortune Drive, San Jose, CA 95131 USA Phone: (408) 954-0522 Fax: (408) 954-0902 EMAIL: sales@geometrics.com...

  • Page 3: Table Of Contents

    7.3.4 SET FORMAT OUTPUT OF DATA ........................29 7.3.5 SAVING SETTINGS IN MEMORY ........................32 7.3.6 START G-824A DATA TRANSMISSION ......................33 7.3.7 Setting the Power Up Mode: ..........................33 7.3.8 XS3 Data Output Format with 1000 Hz Output Rate Example ................34 7.3.9 PPS Synchronization ............................
  • Page 4 APPENDIX A3. SENSOR INSTALLATIONS ................. 47 APPENDIX A4. CESIUM-VAPOR SENSOR THEORY ............52 APPENDIX A.6 G-824A GENERAL BLOCK DIAGRAM OF SYSTEM COMPONENTS ..56 APPENDIX A.7 G-824B GENERAL BLOCK DIAGRAM OF SYSTEM COMPONENTS ..57 LIST OF FIGURES AND TABLES ............

  • Page 5: Introduction

    The G-824 relies on counter circuitry that is internal to the sensor driver module using the Geometrics CM-321 SupremaC counter. Due to licensing concerns we do not offer the G-824 with analog Larmor output for external counting at this time.

  • Page 6: System Components

    2.0 SYSTEM COMPONENTS The basic system components of the G-824A consist of the sensor module, a sensor driver module, and an interconnect cable that is permanently attached to the sensor module and detachable from the sensor driver module. These components are identified in Figures 1 and 2.
  • Page 7 A multi-conductor cable connects the sensor driver module to the junction box and carries power and digital data from the module. The multi-conductor cable may be as long as 200ft (61m) for interconnection with a power/data junction box (e.g., Geometrics Cable P/N 27560-01) Geometrics, Inc.

  • Page 8: Performance

    50,000 nT field the Larmor frequency is about 175 kHz which is converted using a proprietary counting system in the internal CM-321 SupremaC counter. The output of the G-824A is an RS-232 transmission at up to 1000 samples per second. Sensor Active Zone extends from 15º to 75º...

  • Page 9: Installation

    The G-824A is primarily intended for use in airborne and land/ base station applications, and operates over the earth's magnetic field range of 17,000 to 100,000nT. Absolute accuracy (as compared to an international standard) is rated at ± 2nT over the earth’s magnetic field range independent of orientation and does not drift with time.

  • Page 10: Sensor Orientation

    Unless the sensor is very near highly magnetic objects, the local magnetic field will be almost entirely due to the earth’s magnetic field. In order for the G-824A to accurately measure the local magnetic field magnitude, it must be properly oriented relative to the local magnetic field direction.
  • Page 11 The intensity information may be used as a check of the system operation. Geometrics also offers a program called CSAZ which is available for download from our website (Magnetometers, Downloads, Software) and on the supplied Magnetometer CD.
  • Page 12 In this region the magnetic field is nearly horizontal and there may be some restrictions on the direction of flight. Choosing one of the two recommended orientations will allow you to choose flight directions most suitable for your survey area. Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 13 Earth’s magnetic field is greater or equal to 65º. There are no restrictions on the direction of travel when using this sensor orientation. Figure 7 Polar Zone sensor orientation Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 14 There are restrictions on the direction of travel when using this sensor orientation. The bottom diagram to the left shows the flight directions where the sensor will produce adequate signal. These flight directions are 60 wide.. Geometrics, Inc. G-824A Magnetometer Manual...

  • Page 15: Sensor Attachment

    Magnetometer Support CD supplied with your magnetometer. 4.2 Sensor attachment An acceptable mount for the G-824A sensor will provide a stable, non-magnetic attachment to the vehicle, provide vibration dampening and allow the sensor’s orientation to be adjusted with minimal effort. One example of such a mounting solution is the sensor mount available from Geometrics (P/N 27530-04).

  • Page 16: Vibration

    Special care should be taken in securing or routing the cable so that it does not encounter hard or sharp objects that could damage the cable. Those components used to mount the G-824A sensor or any or any objects near this sensor should be non-magnetic in order to minimize the system heading error.

  • Page 17: Temperature

    The G-824A includes an ASCII text based configuration scheme covered in section 7. 6.0 TROUBLE SHOOTING Operation of the G-824A is relatively simple and when trouble arises it is usually easy to recognize and correct. Table 2 shows a troubleshooting guide provided to help in quickly locating the probable cause of the most common system problems.
  • Page 18 Replace cable. consumption. communications cable. Defective sensor or Return sensor and electronics to Geometrics electronics. for repair. Preventing a problem is almost always less costly than correcting the problem. We recommend checking the follow items as part of any new installation or whenever an existing installation is altered.

  • Page 19: G-824A Magnetometer

    Larmor signal for external counting. Digitized Larmor is provided to the user in RS-232 serial format from the G-824A serial port to a host computer (or Serial to USB converter, see Keyspan.com) serial Com port. The RS-232 serial string configuration and other features of the G-824A are configured by the user by choosing options from the G- 824A Configuration Menu.
  • Page 20 The connectors used on the interface cable are of the solder type and they may be removed and reused to suit the application. Table 4 describes the pin-out of the 32 pin connector on the G-824A magnetometer. The interface cable is wired as shown on the schematic in Figure 6.

  • Page 21: Cm-321 Output Format

    7.1 CM-321 Output Format The output data format of the G-824A is programmable. Units are pre-configured at the factory to match end user’s requirements. For example each of the A/D channels can be added or removed from the output data stream by editing the CM-321 configuration page.
  • Page 22 Figure 10 Block Diagram of G-824, power, PPS, and computer connections Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 23 If the data were captured to a file and then printed the output would look like this: $ 99778.1314 $ 99890.3762 $ 99955.5171 $ 99998.2933 $100078.8356 $100032.0718 $ 99979.1595 $ 86778.5089 $ 78778.2166 $ 69978.3474 Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 24 (the default character is a dollar sign, '$'), and all other counters output a different preamble character (the default character is a comma, ','). Figure 11. Schematic diagram of daisy-chained CM-321 counter modules. Figure 12. Wiring diagram of Interface Cable. Geometrics, Inc. G-824A Magnetometer Manual...

  • Page 25: Installing Driver For Usb To Serial Converter

    USB to RS-232 SERIAL port adapter to configure and collect data from the G-824A. If your host computer does have an RS-232 Serial port, you can connect that host computer to the G-824A directly, in which case you may skip this section and advance to section 7.1.2.
  • Page 26 ), as below. Note that the COM port that was assigned to this device by your computer will likely be different from the example shown (COM25). “xx” here denotes port number, which could be different for different PCs and USB ports. Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 27 6. At the resulting “Advanced Settings for COMxx” change the “Receive (Bytes):” to the lowest value possible by clicking on the arrow beside its value setting box and scrolling to the top (lowest) setting available. In this case the lowest setting is Geometrics, Inc. G-824A Magnetometer Manual...

  • Page 28: Installing Tera Term Terminal Emulator

    7.2.2 Installing Tera Term Terminal Emulator A data terminal program capable of bi-directional communication is required to access the G-824A's configuration menu. This is achieved through the host computer's Serial RS-232 Com Port. If you already have a serial terminal program that allows bi- directional serial communication through one of your host computer's Serial RS-232 Com ports, you may skip this step and advance to section 7.3.1.

  • Page 29: Serial Data Interface

    7.2.3 Serial Data Interface A standard RS-232 serial interface is used to communicate with the G-824A. The Port should be set to 8 data bits, 1 stop bit, no parity, and no handshaking. Baud rate must be set to at least 115,200 for high speed (250 Hz or faster sample rates. The same port is used for configuration and data collection.
  • Page 30 Click on the Setup menu item and select Serial port to set the Baud rate, Data bits, Parity, Stop bit, and Flow control communications parameters. The host computer is now ready to receive, display and send configuration commands to the G-824A. Geometrics, Inc. G-824A Magnetometer Manual...

  • Page 31: Ascii Data Output Format With 250 Hz Output Rate Configuration Example

    10 millisecond pulse width. Pulse polarity can be configured in the G- 824 configuration menu as shown in Section 7.3.9: F. Connect the G-824A sensor to its sensor and position the sensor in the proper orientation (approximately 45degrees to magnetic field inclination angle).

  • Page 32: Set Cycle Time (Data Output Rate)

    This is done by setting the time between each cycle, called the cycle time. For a 250 Hz output data rate, 1/250 = 4 milliseconds, so we enter 0.004. From the G-824A configuration menu we type C. The G-824A immediately responds with the following:...

  • Page 33: Set Format Output Of Data

    Cycle time in seconds : 0.004 Use the backspace to edit the number and hit ENTER (0.004 = 250 Hz) The G-824A accepts the reading and re-displays the configuration menu for the user (below). File (Safe default values# (Not saved) S/N 824113 CM321 configuration Version 00.02...
  • Page 34 ADC[4] display position (0=none,1=first,2=second..etc) : 0 ADC[4] display format :####.### ADC[5] display position (0=none,1=first,2=second..etc) : 0 ADC[5] display format :####.### ADC[6] display position (0=none,1=first,2=second..etc) : 0 ADC[6] display format :####.### ADC[7] display position (0=none,1=first,2=second..etc) : 0 ADC[7] display format :####.### Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 35 Status display format :## Format ## Include a CheckSum in the data : (0=No 1=Yes ):0 Character to put before the checksum for ASCII data :* Postamble for ASCII data :\r\n Postamble for XS3 data :* Geometrics, Inc. G-824A Magnetometer Manual...

  • Page 36: Saving Settings In Memory

    7.3.5 SAVING SETTINGS IN MEMORY The next step is to save the adjusted settings in the G-824A memory such that they will then be what will be used the next time the magnetometer is powered on. To do this, type S at the Configuration Menu prompt.

  • Page 37: Start G-824A Data Transmission

    7.3.6 START G-824A DATA TRANSMISSION Now that the G-824A has been configured and the settings saved the settings in the magnetometers flash memory, the magnetometer can be commanded to start outputting readings from the Configuration menu by typing R. The following is observed:...

  • Page 38: Xs3 Data Output Format With 1000 Hz Output Rate Example

    The power up Mode is now saved. 7.3.8 XS3 Data Output Format with 1000 Hz Output Rate Example XS3 is an alternate compressed binary data output format that the G-824A can accommodate for high speed data transmissions. The key advantage of this format is that it can pack two bytes of text into one ASCII character.
  • Page 39 To set up the G-824A to output at a 1000 Hz rate, record the Larmor signal level (to allow sensor orientation adjustment) and record the Status/ PPS Byte (for synchronization of the data and to confirm proper magnetometer operation), perform the following procedures: 1.
  • Page 40 Pressure supply monitor display position (0=none,1=first,2=second..etc) : 0 Pressure supply monitor display format :##.# Sounder supply monitor display position (0=none,1=first,2=second..etc) : 0 Sounder supply monitor display format :###.# Fluxgate supply monitor display position (0=none,1=first,2=second..etc) : 0 Fluxgate supply monitor display format :##.# Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 41 You can now type R to run the magnetometer and view the XS3 data being output at 1000 Hz. A description of the XS3 format (including decoding) is in section 7.4. The following is an XS3 data example (note $=start,*=end). $[ˆ9“63*$[ˆ9˜63*$[ˆ9›63*$[ˆ9œ63*$[ˆ9š63*$[ˆ9•63*$[ˆ9Š63*$[ˆ9Š63*$[ˆ9‹63*$[ˆ9•63*$[ˆ9£63*$[ˆ9¥63*$[ˆ9š63*$[ˆ9”63*$[ˆ9“ 63*$[ˆ9•63*$[ˆ9•63*$[ˆ9”63*$[ˆ9•63*$[ˆ9˜63*$[ˆ9›63*$[ˆ9›63*$[ˆ963*$[ˆ9Š63*$[ˆ9ˆ63*$[ˆ9“63*$[ˆ9š63*$[ˆ9š63*$[ˆ9™63*$[ˆ 9—63*$[ˆ9Œ63*$[ˆ9‰63*$[ˆ9‹63*$[ˆ9“63*$[ˆ9•63*$[ˆ9˜63*$[ˆ9˜63*$[ˆ9˜63*$[ˆ9—63*$[ˆ9”63*$[ˆ9‹63*$[ˆ9Œ63*$[ˆ9– 63*$[ˆ9š63*$[ˆ9›63*$[ˆ9š63*$[ˆ9™63*$[ˆ9”63*$[ˆ9‰63*$[ˆ9Š63*$[ˆ9•63*$[ˆ9›63*$[ˆ9¥63*$[ˆ9¤63*$[ˆ9š63*$[ˆ9– 63*$[ˆ9‹63*$[ˆ9Š63*$[ˆ9”63*$[ˆ9™63*$[ˆ9¤63*$[ˆ9¤63*$[ˆ9›63*$[ˆ963*$[ˆ9“63*$[ˆ9Š63*$[ˆ9‰63*$[ˆ9Š63*$[ˆ9•63*$[ˆ9™6 3*$[ˆ9˜63*$[ˆ9”63*$[ˆ9‹63*$[ˆ9Œ63*$[ˆ9Œ63*$[ˆ9Œ63*$[ˆ9–63*$[ˆ9›63*$[ˆ9£63*$[ˆ9œ63*$[ˆ9–63*$[ˆ9Œ63* Geometrics, Inc. G-824A Magnetometer Manual...

  • Page 42: Pps Synchronization

    Almost all survey-grade GPS receivers have a PPS output. This PPS can be connected via the shielded twisted pair cable that comes out of the G-824A Interface cable for mag data synchronization with GPS (see Figure 13). The G-824A PPS input can be configured in the G-824A with a positive pulse (trigger on the rising edge) or a negative pulse (trigger on the falling edge).

  • Page 43: Magnetometer Operational Status

    $ 28550.66295 3.5 0 1 here in the status column indicates that this reading is $ 28550.66333 3.5 1 synchronized to a PPS event as seen by the G-824A’s PPS input. $ 28550.66359 3.5 0 Here is an example on how to turn on the 1 pps phase locking function. From the main configuration menu select T to get to the triggering submenu.

  • Page 44: Xs3 Data Output Format

    ASCII byte, doubling the amount of data that can be sent to the host computer by the G-824A. This is an important feature as it helps address the limitation of the magnetometer's 115,200 baud rate when outputting data at the full 1000 readings per second.

  • Page 45: G-824A Warm-Up Time

    The third is the status value. 7.5 G-824A Warm-up Time The sensor requires 5 to 15 minutes for warm-up. This time is required for the G-824A to stabilize and transmit valid field readings. This warm-up time depends on the ambient temperature at the sensor and can be monitored by using the Larmor signal level.

  • Page 46: G-824B Magnetometer

    G-824A with the exception of its heading error. G-824B heading error is larger than the “A” sensors and not specified. As with the G-824A, the G-824B is shipped with a 25ft external signal/power interface cable, a power/data junction box, and an RS-232 data cable.
  • Page 47 Positioning the sensor off the ground will reduce the gradients arising for the soil or from outcrops. It is also important to provide a rigid support structure to keep wind induced motion to a minimum. Figure 7 shows a base station installation that uses a kit supplied by Geometrics for this purpose. G-824B magnetometer...

  • Page 48: Accessory Software

    CD and from our FTP site at ftp://geom.geometrics.com/pub/mag/Software/ (see csaz-setup.exe). Please read the manual that is included with the program for complete instructions on how to use the CSAZ program for worldwide inclination and sensor orientation solutions. Geometrics, Inc. G-824A Magnetometer Manual...

  • Page 49: Appendix A1. Model G-824A Specifications

    APPENDIX A1. MODEL G-824A SPECIFICATIONS Self-oscillating split-beam Cesium Vapor (non- PERATING RINCIPLE radioactive) 20,000 to 100,000 nT PERATING ANGE The earth’s field vector should be at an angle greater PERATING ONES than 6º from the sensor’s equator and greater than 6º...

  • Page 50: Appendix A2. Model G-824B Specifications

    9 pin RS-232 connector and power lugs), lengths to be specified, spare O rings, operation manual and carrying case Optional: Birds, Stingers, Wingtips, Avionics, GPS receivers SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE Geometrics, Inc. G-824A Magnetometer Manual...

  • Page 51: Appendix A3. Sensor Installations

    APPENDIX A3. SENSOR INSTALLATIONS Figure A1. G-824A sensor and G-824A Bird components Figure A2. Airborne Stinger showing sensor mount. Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 52 Figure A3. Aircraft fitted with stinger assembly Figure A4. Aircraft fitted with horizontal transverse and longitudinal gradiometer using faired wingtips and stinger. Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 53 Figure A5. G-824A Boom installation on Ultra-lite autogyro. Figure A6. Single sensor boom installation on Helicopter. Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 54 Figure A7. Multi-sensor (7) MTADS Helicopter installation for UXO survey. Figure A8. Rack mount for airborne geophysical survey system Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 55 Figure A9. MTADS multi-sensor array for UXO survey applications. Figure A10. Multi-sensor array on cart for UXO or archaeological surveying. Geometrics, Inc. G-824A Magnetometer Manual...

  • Page 56: Appendix A4. Cesium-Vapor Sensor Theory

    Absorption Cell Polarizer Figure A11. G-824A cesium-vapor To initiate operation of the sensor, the lamp oscillator's RF power increases until the lamp strikes (plasma ignites and fluoresces). The lamp oscillator then reduces its power to produce the regulated amount of light. The heater warms the absorption cell until a Cesium vapor is formed.
  • Page 57 Once most of the Cesium atoms have absorbed photons and are in a state that does not allow them to absorb another photon, the light absorption of the cell is greatly reduced, Geometrics, Inc. G-824A Magnetometer Manual...
  • Page 58 In Cesium this Larmor frequency is exactly 3.498572 times the ambient field measured in nano-teslas (gammas). In the G-824A this radio frequency field is generated by a coil, called the H1 coil that is wound around the tube holding the optical components. When the R.F.

  • Page 60: Appendix A.6 G-824A General Block Diagram Of System Components

    APPENDIX A.6 G-824A GENERAL BLOCK DIAGRAM OF SYSTEM COMPONENTS G-824A CESIUM MAGNETOMETER SHIP KIT APPLICATION G-824 SENSOR OPERATION AND SPECIFIC MOUNTING & ELECTRONICS TECHNICAL MANUAL 27559-01 AND INTERFACE 27735-xx 27731-OM HARDWARE 27516-xx SENSOR PACKAGE SENSOR PHYSICS CARRYING CASE ASSEMBLY PACKAGE...

  • Page 61: Appendix A.7 G-824B General Block Diagram Of System Components

    APPENDIX A.7 G-824B GENERAL BLOCK DIAGRAM OF SYSTEM COMPONENTS G-824B CESIUM MAGNETOMETER SHIP KIT APPLICATION G-824 SENSOR OPERATION AND SPECIFIC MOUNTING & ELECTRONICS TECHNICAL MANUAL 27559-01 AND INTERFACE 27735-xx HARDWARE 27516-xx 27731-OM SENSOR PACKAGE SENSOR PHYSICS CARRYING CASE ASSEMBLY PACKAGE 27516-xx 320438-220 27615-01...

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