FDEM-8 SYSTEM

[General Description] [System Specifications] [Signal Display] [Software & Data Sample]
[Price & Ordering Information]

GENERAL DESCRIPTION

fClick here to see a larger pic of the Barlow EM System transmitter & receiverThe FDEM-8 is an affordable frequency domain electromagnetic (FDEM) measurement instrument, consisting of  two coils, a transmitter (Tx), a receiver(Rx), and a reference cable. In operation, the coils are spaced ten to fifty meters apart. At every station along the survey the system takes approximately 15 seconds in total to cycle through 8 frequencies, measuring the in-phase and quadrature components (amplitude & phase) for each. Each frequency provides information covering a different depth at that specific station. Combining the data for all 8 frequencies allows the operator to create a pseudo-section along the survey line.

The transmitter is controlled by the receiver which, in turn, serves as the data acquisition system. Data are saved on the receiver for later downloading to an IBM-compatible computer. During the survey the data are also displayed on an LCD screen, allowing the operator to get an idea of the data quality, signal strength, and underlying geology.

Although externally the FDEM-8 appears similar to other well known EM systems, the FDEM-8 requires only a single traverse to build up a pseudo-section (it utilizes multiple frequency signals at each station to obtain information from varying depths).

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SPECIFICATIONS

Click here for larger pic of EM system in shipping caseThe instrument consists of a transmitter and a receiver and two coils. The transmitter and the receiver are linked with a synchronization cable. Both instruments are housed in a sturdy wooden box and are carried with a sling around the neck of the operator. These instruments use rechargeable sealed lead acid batteries. The total shipping mass of the receiver and transmitter is 24,5 kg and that of the two coils is 18.5 kg.

RECEIVER

The receiver has the following specifications:

  1. Click here for larger pic of EM receiver, showing details of the control panelIt has eight measurement frequencies: 37, 75, 150, 300, 600, 1200, 2400 and 4800 hertz.
  2. From one to eight frequencies can be read at each station.
  3. A reference signal is generated for the transmitter i.e. the transmitter is a slave to the receiver.
  4. The receiver is menu driven and input from the operator is via a 16-key, keypad.
  5. The display is via an alphanumeric graphic LCD with a viewing area of 132 x 38 mm and resolution of 240 x 64 dpi.
  6. During a measurement cycle, frequencies and gain of the amplifier are automatically selected. A measurement is made with a single push of a button. A reading (all 8 frequencies) takes approximately 15 seconds.
  7. Readings of amplitude and phase of the received signal is saved in non-volatile RAM for retrieval.
  8. Up to 600 readings (8 frequencies each) can be saved to memory before data must be downloaded. Data can be organized in different numbered lines. For graphic display, maximum line length is 140 stations.
  9. Readings are plotted or displayed on the LCD screen in real time.
  10. The receiver has a rechargeable sealed lead-acid battery with low battery and battery discharged LED indicators. Up to 20 hours of operation can be obtained from the battery.
  11. The battery is charged with an external 220VAC power supply. A 120VAC charger can be supplied on request. A "charge-in-progress" indicator is mounted on the receiver.
  12. The dimensions of the receiver are 260 x 170 x 200 mm and the mass is 5.5 kg.
  13. The receiver has a RS232 interface (serial port) for down loading data to a PC.
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TRANSMITTER

The transmitter has the following specifications:

  1. Click here to see larger pic of EM transmitter, showing details of control panelThe transmitter is a slave to the receiver. It amplifies and transmits the signal received, from the receiver, to the transmitter coil.
  2. The transmitter has a rechargeable sealed lead-acid battery with low battery and battery discharged LED indicators. Up to 10 hours of operation can be obtained from the battery.
  3. The battery is charged with an external 220VAC power supply. A 120VAC charger can be supplied on request. A "charge-in-progress" indicator is mounted on the transmitter.
  4. The dimensions of the transmitter are 220 x 75 x 225 mm and the mass is 6kg

The transmitter has the following output characteristics:

Frequency Output Current (mA) Output Power (Atm2)
4800 143 3.24
2400 223 5.06
1200 413 9.37
600 752 8.91
300 1203 27.29
150 1529 34.68
75 1639 37.18
37 1577 35.77

COILS

Click here for larger pic of EM coil in shipping caseThere are two coils, a transmitter (Tx) and a receiver (Rx). The dimensions of these coils are both 760 x 40 mm, and the mass of each is 2.5 kg. The Tx & Rx coils are connected by cable to the transmitter and receiver respectively. The receiver coil has an effective area of 180 m2

 

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SIGNAL DISPLAY

While surveying with the FDEM-8 there is an option in the DATA menu to display, in bar graph format, the signal strength of all eight frequencies. This is displayed in the left-hand box. The phase measurement for the eight frequencies is displayed in the right hand box. This bar graph can be used to decide which frequencies to display while the traverse is made, or to determine whether any noise is present.

data_display.gif (2707 bytes)

Measured readings can be displayed graphically, in real-time, during the making of a traverse (Amplitude on LHS, phase on RHS)
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SOFTWARE SUPPLIED WITH THE FDEM-8

Downloading data to PC. Click for larger image (20819 bytes) Software is supplied to download the data from the receiver to a PC. Data is written to ASCII files that can easily be read by spreadsheet software (e.g. MS Excel.). Data can also be saved in".DAT" format for direct use in Surfer for Windows.

The program supplied allows the operator to:

  1. Download data.
  2. Save data to disk.
  3. Join multiple lines into a single line or file.
  4. Plot the amplitude and phase of the signal and make a hardcopy.
  5. Plot the field data to screen or printer.
  6. Plot a pseudosection, which can be color filled.
  7. Convert data to files for use with a spreadsheet and Surfer.
  8. Select the COM port to use.
The plot shown alongside is the amplitude data from a survey over a known fault zone in a sedimentary formation. The data was converted to Surfer format, gridded, contoured and imaged. Sample data from FDEM-8 (10727 bytes)
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