Features

General

The Melis CSEM system consists of a two channel receiver and a 3,000 Watt transmitter called the TX 3000. The Melis receiver may be used in a classical controlled source audio magnetotelluric mode (CSAMT) or in a controlled source electromagnetic mode (CSEM) with a surface loop source and either surface electric and magnetic sensors; or using the Remi, borehole receiver, in a surface to borehole mode.

The Melis receiver features a dual channel spectrum analyzer for simultaneous measurement of signal amplitude and relative phase. Three input ports are provided for two magnetic components and one electric component. Nearly any frequency in the range 0.1 to 8000 Hz can be analyzed. Using a Fast Fourier Transform (FFT) the signal to noise ratio is calculated during the measurement. This is done by comparing the amplitude of the signal at the frequency being measured to amplitudes of signals at frequencies close to the one being measured.

During stacking each measurement is weighted to give signals with less noise more weight than signals that are noisier. In this way the stacking time can be minimized. The operator monitors the measurement process through continuous updates on the display. At the end of the measurement resistivity values with corresponding standard deviations are displayed.

The Melis receiver will simultaneously measure several frequencies through a multifrequency mode. When using a symmetrical square wave signal the base frequency F and the harmonics 3F are measured; when using a nonsymmetrical signal the base frequency F plus harmonics 2F and 3F are measured. This mode is most useful for measurements in the central part of the frequency range.

An internal reference signal may be used to check the system calibration in the field. The reference signal is sent to the sensors and a measurement cycle is run. Comparisons of amplitude and phase correction coefficients provide verification of system status.

Melis Modes

Melis receiver can be operated in various source/sensors combinations:

TX 3000 CSAMT Transmitter

Features

General

The TX 3000 is a light weight transmitter for CSAMT or CSEM applications. It offers a frequency range of 0.1 Hz to 18 KHz in binary steps. Two square waveforms are available to support single and multiple frequency modes.

The four line LCD display provides values for impedance, output current, output voltage, output power, and output frequency. The previously used values for intensity and frequency may be stored so that set up at the next station is faster.

REMI EM Probe

General

The Remi is an EM probe for borehole measurements of the axial component of the magnetic field produced by laying a loop on the earth's surface. It is connected to the Melis receiver for discrete measurements through a four-conductor cable. The aim of this type of measurement is to detect conductive bodies located near a drill hole that may have been missed. The Remi is thus a downhole CMS magnetic sensor. Its frequency range is 2Hz to 8kHz, with a sensitivity of 50 mV/gamma.

Specifications

Melis Receiver

Frequency range: 0.12Hz to 8000Hz

Three input ports: Hz, Hr, Et

Two simultaneous measuring channels (two magnetic or one magnetic and one electric)

Measurement, computation and display of amplitudes and relative phases of components, standard deviations and quality coefficient

Notch filters: 50 or 60Hz and harmonics

Digital filtering and measurement by FFT (256 points per channel)

Window: Uniform or Hamming

StackingPprocess(selective): through weight coefficients depending on signal/noise ratio

Sensors and receiver calibration: Laboratory mode: ROM stored coefficients Field mode: In-the-field calibration

Data storage in solid state memory: 256 records

RS232 port for transferring data to PC computer

Dimensions: 22x31x33cm

Weight: 7kg

Operation temperature range: -20°C to +50°C

Power supply: Nine 1.5V D size dry cells or external 12V DC supply.

Melis Sensor

Electric line: Differential measurement with 20m long electric line and three metallic electrodes.

CMS magnetic sensor: Frequency range: 2Hz to 10kHz Sensitivity: 50mV/gamma Flux feed back coil Low noise system Diameter: 5cm Length: 35cm Weight: 1.5kg Frame for mounting two orthogonal sensors.

CMU magnetic sensor: Frequency range: 0.1Hz to 7.5kHz Extremely low noise sensor Sensitivity: 100mV/gamma Flux feed back coil Diameter: 9cm Length: 1m Weight: 7kg Frame for mounting two orthogonal sensors.

TX 3000

Maximum output power: 3,000W

Maximum output current: 20A on a maximum resistive load of 7.5 ohms

Maximum output voltage: 800V

Minimum load resistance: 2 Ohms

Power efficiency: 85%

Input voltage: 220V ± 10%, 50/60Hz

Input voltage galvanometer

Frequency range: 0.1Hz to 18kHz: 0.14, 0.27, 0.55, 1.09, 2.19, 4.38, 8.75, 17.5, 35, 70, 140, 280, 560, 1120, 2240, 4480, 8960, 17920Hz

Crystal controlled timing

Square current waveform: ON+, ON- symmetrical mode: ON+ = ½ ON- = ½ unsymmetrical mode: ON+ = ¼ ON- = ¾

Reference signal: Output for phase and/or for amplitude check

Display: A four line LCD display gives the values impedance, output current, output voltage, output power, output frequency.

Thermal protection: Automatic thermal shut off for internal over temperature.

Other protection: Automatic turn off in case of overloads, short circuits, open circuits.

Fan cooling

Option: TX 3000 can be controlled by a microcomputer through a RS 232 serial link: turn on, turn off, change of frequency, and intensity.

REMI

Cable: 4 conductors with armored shield

Cable Head: Gearhart-Owen type

Probe Diameter: 38mm

Length: 1.40m

Weight: 4kg

Standard Components

Melis console, receiver, 2 CMS magnetic sensors, 10m electric line with 3 electrodes, transmitting loop (400m), motor generator with 20m cable, and instruction manuals.

Ordering Information

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