[General Description] [System Specifications] [Signal Display] [Software
& Data Sample]
& Ordering Information]
The 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
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).
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
The receiver has the following specifications:
has eight measurement frequencies: 37, 75, 150,
300, 600, 1200, 2400 and 4800 hertz.
- From one to eight frequencies can be read at each
- A reference signal is generated for the
transmitter i.e. the transmitter is a slave to
- The receiver is menu driven and input from the
operator is via a 16-key, keypad.
- The display is via an alphanumeric graphic LCD
with a viewing area of 132 x 38 mm and resolution
of 240 x 64 dpi.
- 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.
- Readings of amplitude and phase of the received
signal is saved in non-volatile RAM for
- 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.
- Readings are plotted or displayed on the LCD
screen in real time.
- 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.
- 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.
- The dimensions of the receiver are 260 x 170 x
200 mm and the mass is 5.5 kg.
- The receiver has a RS232 interface (serial port)
for down loading data to a PC.
The transmitter has the following specifications:
transmitter is a slave to the receiver. It amplifies and
transmits the signal received, from the receiver, to the
- 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.
- 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.
- The dimensions of the transmitter are 220 x 75 x 225 mm
and the mass is 6kg
The transmitter has the following output characteristics:
||Output Current (mA)
||Output Power (Atm2)
There 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
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.
|Measured readings can be
displayed graphically, in real-time, during the making of
a traverse (Amplitude on LHS, phase on RHS)
SOFTWARE SUPPLIED WITH THE FDEM-8
||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
The program supplied allows the operator to:
- Download data.
- Save data to disk.
- Join multiple lines into a single
line or file.
- Plot the amplitude
and phase of the signal and make a
- Plot the field data
to screen or printer.
- Plot a pseudosection,
which can be color filled.
- Convert data to files
for use with a spreadsheet and Surfer.
- 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.