1. Audiomagnetotelluric sounding system ACF-4
2. ACF - 2.2
Audiomagnetotelluric
sounding system ACF-4
Main features :
Purpose :
geoelectrical prospecting with penetration depth up to several kilometers using audio frequency magnetotelluric soundings and controlled source audiomagnetotellurics.
Application :
Structural studies, geothermal investigations, oil and gas exploration, search for deep-seated mineral deposits.
Description
The equipment is a modern portable instrument for audio frequency
magnetotellurics, intended for natural and artificial electromagnetic field measurements
in the frequency range 1 to 3200 Hz, real time measurement data processing and storage of
processing results.
The equipment
consists of three main parts:
- the 4 channel microprocessor-based measuring unit and RS-232C interface,
- electric lines (2 pcs) and magnetic field sensors (2 pcs),
- calibration unit (noise generator and induction loop).
The system control, calculations and visualization of spectral
functions, storage of results of processing are made with using an IBM-compatible notebook
computer.
Usage of the instrument in a complex together with the standard low-frequency
magnetotelluric equipment provides :
- acquisition of a full-range sounding curve, reflecting the resistivity structure from
tens of meters up to several tens of kilometers;
- correction of MT curves, considering their distortion because of local discontinuities
in the resistivity structure.
Using stored correlation functions values, computed by the microprocessor of the measuring block, a notebook computer calculates auto and cross spectra power densities SExEx, SEyEy, SHxHx, SHyHy, SExHy, SEyHx, SExHx, SEyHy, SExEy, SHxHy.
The visualization program displays on the computer screen the
following parameters:
- auto and cross spectra, coherences and phase differences vs. frequency for each;
- pair of measuring channels.
Technical data
Measuring block
| Number of simultaneous measuring channels ( 16-bit ADC per channel): | 4 |
|
| Frequency range | 1- 3200 Hz |
|
| Number of separate frequency bands ( 200 Hz width) | 16 |
|
| Spectral resolution | 0.78 Hz |
|
| Input voltage range (at “harmonic signal / noise” ratio equal to 10 ) | 1-30000 mkV |
|
| Noise level | 150 nV/Hz1/2 |
|
| Built-in RAM | 64 kB |
|
| Internal power supply (
3.5 A*h) Resource |
12± 2 V 8 hours |
|
| Operating temperature range | 0° -40° C |
|
| Dimensions and weight : Measuring block Noise generator Induction loop Recharging unit External battery |
mm 400 x 170 x 300 200 x 90 x 125 5000 x 5000 200 x 90 x 100 69 x 72 x 176 |
kg 5.5 1.8 1.5 1.5 1.7 |
| Frequency
range main additional |
10-4000 Hz 1-10 Hz |
|
| Output
sensitivity main frequency range additional |
50+2.5 nT/Hz1/2 5+0.25 nT/Hz1/2 |
|
| Equivalent
magnetic noise at 10 Hz at 1000 Hz |
37 fT/Hz1/2 2 fT/Hz1/2 |
|
| External power supply | ± 12± 2 V |
|
| Interface cable length | 6 m |
|
| Operating temperature range | -10° ... +50° C |
|
| Dimensions ( diameter x length) and weight | mm 110 x 1040 |
kg 6.8 |
Standard components:
Measuring block, noise generator, generator loop, external batteries (2 pcs), recharging unit, induction coil sensor (2 pcs), brass electrodes (4 pcs),a set of cables and accessories , application software floppy disks set, operation manual.
Optionally a notebook computer may be included.
Developer :
Earth Crust Institute of St.Petersburg State University, 199034, St.Petersburg , Universitetskaya nab., 7/9
Manufacturer : “Geologorazvedka” GNPP
The new ACF-2.2 system is designed for natural and controlled source electromagnetic field measurements. This 2 channel instrument operates in 3 various modes .
1. The broad band mode : determination of co- and cross spectral power densities through the corresponding stacked correlation functions in the operating frequency range 5 - 300 Hz ( sampling rate 675 Hz, resolution 0.78 Hz). This mode is standard for natural field audio magnetotellurics.
2. The narrow band mode : determination of co- and cross spectra in the bands of 2 Hz width at several pre-programmed central frequencies. Spectral resolution when working in this mode is about 0.007 Hz. The mode is used for the ELF transmitting station electromagnetic field measurements.
3. The time series mode : storage of time series of electric and magnetic field for post-acquisition processing, up to approximately 200000 samples per channel, sampling rate 675 Hz.
A notebook computer is used only for transferring stored data ( correlation functions or time series ) from instrument‘s built-in RAM to hard disk through RS-232 interface and on site spectra calculations for real time evaluation of measurement quality, rather then for data acquisition.
Information support and design © RSoft, Ltd. 1998