.. _mfs-06e:
.. |br| raw:: html
MFS-06e MK-II
===============
Since serial number 1077 the MFS-06e is equipped with a new preamplifier.
The noise level is reduced and *power consumption has dropped down from 25mA to 15mA*.
Product Description
----------------------
The broadband induction coil magnetometer MFS-06e has been developed
to measure variations of the Earth´s magnetic field, particularly for
applications in Magnetotellurics (MT) and Controlled Source Audio
Magnetotellurics (CSAMT). It covers a wide frequency range from 0.0001
Hz up to 10 kHz. In spite of its broad bandwidth, the MFS-06e shows
outstanding low-noise characteristics, extremely low temperature drift
of input offset voltage and offset current and a very stable transfer
function over temperature and time. The MFS-06e is the result of many
years of experience of metronix in the design, manufacture and
application of induction coil magnetometers. As a unique feature the
MFS-06e acts as an "intelligent plug and play" sensor. Thus, once
connected to the ADU-07e, it will send its type and serial number as
well as its calibration function to the ADU-07e automatically. The
user does not have to care about any further sensor parameter setup.
metronix magnetometers have been used by numerous customers throughout
the world - including geophysical exploration companies and research
institutes.
.. image:: /media/mfs-06e/uli_mfs-06e_crop_small_black.jpg
:width: 50%
:align: center
A complete magnetic field measurement site consists of three single axis
orthogonal sensors. Each sensor is enclosed in a shock resistant
cylindrical tube that acts as a protection against mechanical stress.
These tubes are waterproof and also resistant to ultraviolet radiation.
The magnetometer contains the electronics for pre-amplification of the
sensor signal as well as for precise self calibration. The MFS-06e
magnetometer is connected to the metronix ADU-07e data logger (or any
other custom electronics) by a cable of up to 70 m in length. Special
care is taken to the fact that magnetometers are often used under rough
environmental influences. All cables have ruggedized waterproof
connectors. The very high quality of the MFS-06e data is achieved by a
unique design for the ultra low noise and low frequency preamplifier.
Features
^^^^^^^^
The MFS-06e has several outstanding features which make it a first
class instrument for the electromagnetic exploration:
* Wide frequency range from 1/10000 Hz to 10 kHz covered by only one
sensor
* High linearity
* Ultra low noise
* High accuracy calibration with built-in precision calibration
facility
* Wide operating temperature range from -25° C to +70° C
* high stability of the sensor´s transfer function due to magnetic
field feedback
* built-in signal amplification and conditioning electronics
* Metronix "Smart Sensor" technology – sensor parameters incl. transfer
function can be read by ADU-07e automatically
* easy field handling: one person can carry two magnetometers all at
once
Technical Data
^^^^^^^^^^^^^^
.. csv-table::
:delim: |
Frequency range|0.0001 Hz ..... 10 kHz
Frequency bands|0.0001 Hz ..... 500 Hz (chopper on)
|10 Hz ....10 kHz (chopper off)
Sensor noise|:math:`1 \cdot 10^{- 2} nT/\sqrt{Hz}~@~0.01 Hz`
|:math:`1.1 \cdot 10^{- 4} nT/\sqrt{Hz}~@~1 Hz`
|:math:`1 \cdot 10^{- 6} nT/\sqrt{Hz}~@~1000 Hz` (chopper off)
Output sensitivity|0.2 V/(nT*Hz) f<< 4Hz
|0.8 V/nT f>> 4Hz
|for exact values refer to individual calibration file
Output voltage range |+/- 10V
Function|induction coil with magnetic field feed back
Connector|10 pole ODU Series K
Calibration coil sensitivity|4 nT / V
Feedback cut-off frequency|4 Hz
Supply voltage|+/- 12V to +/-15V stabilised and filtered
Supply current|+/- 25mA
Case|ruggedized, waterproof glass fibre reinforced case
Weight|ca. 8.5 kg
External dimensions|length 1150 mm, diameter 75mm
Operating temperature range|-25° C ..... + 70°C
Sensor
------------
The central part of the MFS-06e magnetometer is the sensor coil. It
consists of a high permeable ferrite core and several thousand turns of
copper wire. Due to its low skin depth the core material prevents the
occurrence of eddy currents in the measurement frequency range.
To achieve good mechanical stability the main structure of the sensor is
based on the cylindrical tube which is made of fibre glass reinforced
epoxy.
Induction coil sensors do not measure the magnetic field itself but its
time derivative. This is expressed in the law of induction:
:math:`V_{ind} = n \cdot \frac{d\Phi}{dt}`
with
.. csv-table::
:delim: |
:math:`V_{ind}`|induction voltage
:math:`n`|number of turns
:math:`\Phi`|magnetic flux
The flux :math:`\ \Phi` which flows through one loop of the coil is calculated as
:math:`\ \Phi = B \cdot A = \mu_{0} \cdot \mu_{c} \cdot H \cdot A`
with
.. csv-table::
:delim: |
:math:`B`|magnetic flux density parallel to the sensor axis
:math:`\mu_{0}`|permeability constant
:math:`\mu_{c}`|permeability of the core
:math:`A`|cross section of the core
:math:`\overset{\sim}{H}`|magnetic field amplitude :math:`(= \hat{H} \cdot e^{j\omega t})`
:math:`f`|frequency
For a sinusoidal magnetic field which can be written with a phasor as
:math:`\overset{\sim}{H} = \hat{H} \cdot e^{j\omega t}` the induced
voltage of the sensor output becomes
:math:`{\overset{\sim}{V}}_{ind} = {\hat{V}}_{ind} \cdot e^{j\omega \cdot t} = j \cdot \underset{S_{0}}{\underbrace{2\pi \cdot n \cdot \mu_{0}\mu_{c} \cdot A}} \cdot f \cdot \hat{H} \cdot e^{j\omega \cdot t} = j \cdot f \cdot S_{0} \cdot \overset{\sim}{H}`
:math:`S_{0}` is defined as the sensor’s sensitivity constant which
gives the relation between the magnetic field’s amplitude and the
induction voltage. This equation is only a theoretically one. A non
ideal sensor’s equivalent circuit does not only contain the field
proportional voltage source (which itself is not really proportional)
but also some further elements:
.. figure:: /media/mfs-06e/simplified_equivalent_circuit_diagramm_for_a_sensor_coil.jpg
:width: 80%
:align: center
Simplified equivalent circuit diagram for a sensor coil
Referring to the source, the induced sensor voltage :math:`V_{ind}`, the
coil resistance :math:`R`, the input resistance of the amplifier
:math:`R_{d}` the coil inductivity :math:`L` and the capacity :math:`L`
yield a damped serial resonance circuitry. The transfer function of the
sensor will show a strong peak at its resonance frequency.
For the sensor itself, without the preamplifier, we get the transfer
function
:math:`\frac{V_{e}}{V_{ind}} = \frac{\left. {R_{d}/\left( R_{d} + R \right.} \right)}{1 - \left( f/f_{0})^{2} + j \cdot 2D \cdot \left( f/f_{0} \right) \right.}`
with the amplifier’s input resistance :math:`R_{d}`, Gain :math:`G`, resonance
frequency :math:`f_{0}` and attenuation :math:`D` defined as
:math:`f_{0} = \frac{1}{2\pi \cdot \sqrt{a \cdot L \cdot C}}`
:math:`~a = \frac{R_{d}}{R + R_{d}}`
:math:`G = \frac{V_{M}}{V_{e}}`
:math:`2D = \sqrt{\frac{R_{d}}{R_{d} + R}} \cdot \frac{\sqrt{L/C}}{R_{d}} + \frac{R}{\sqrt{L/C}}`
Having this in mind the resulting transfer function between the magnetic
field and the sensor output voltage becomes
:math:`F_{sensor} = \frac{\hspace{0pt}\hspace{0pt}\hspace{0pt}V_{e}}{\overset{\sim}{H}} = \frac{j \cdot S_{0} \cdot {R_{d}/\left( R_{d} + R \right)} \cdot f}{1 - \left( f/f_{0})^{2} + j \cdot 2D \cdot \left( f/f_{0} \right) \right.}`
The equivalent circuit diagram of the magnetometer leads to a frequency
dependent sensitivity :math:`E(f)` referred to the preamplifier output of:
:math:`E\left( f \right) = E_{0} \cdot \frac{V_{e}}{V_{ind}}`
with
:math:`E_{0} = G \cdot S_{0}`
.. figure:: /media/mfs-06e/relative_frequency_response_of_magnetometer_MFS-06e.jpg
:width: 80%
:align: center
Relative frequency response of magnetometer MFS-06e for :math:`H(f) = const`.
The Figure above shows the principle frequency response of the output voltage
:math:`V_{m}` of the MFS-06e. Considering the feedback, the output
voltage is given by:
:math:`V_{M}\left( f \right) = \frac{j \cdot f \cdot H\left( f \right) \cdot E\left( f \right)}{1 + j\frac{f}{f_{c}}}`
The cut-off frequency of the magnetometer is set to :math:`f_{c} = 4Hz`.
Please consider that this figure shall only explain the feedback
principle. Additional effects caused by the low-pass filtering of the
sensor signal at :math:`8192 Hz` and other influences are not respected here.
Preamplifier
----------------
The integrated preamplifier performs the signal amplification of the
sensor output voltage as well as the conditioning of the magnetic field
feedback signal and allows to feed-in an external calibration signal.
Special care has been taken to avoid disturbance of the electronics by
external electromagnetic noise.
To achieve DC characteristics close to the physical limits, the
preamplification electronics is split into a lower frequency path
(low-pass corner frequency :math:`330 Hz`) which is chopper stabilized
in order to achieve excellent low-noise and drift characteristics and
a separate AC path with the same corner frequency. The output signals
of these two amplification paths are used as an input for the magnetic
feedback conditioning stage.
The following block diagram explains the design:
.. figure:: /media/mfs-06e/mfs-06e_block_diagramm.jpg
:width: 80%
:align: center
MFS-06e block diagram
The resulting frequency characteristics of the MFS-06e sensor system
is dominated by the feedback loop. As it was demonstrated in chapter 2
of this manual, the characteristics of the sensor itself mostly depends
on the resonance circuit formed by the main impedance and main capacity
of the coil. This leads to a strong peek in the spectrum at the
resonance frequency :math:`f_{0}`.
In the block diagram above the summing function for the input node leads
to the transfer function, assuming that :math:`U_{pre}` is the output
voltage of the amplifier input stage:
:math:`\left( H - U_{pre} \cdot F_{FB} \right) \cdot F_{sensor} \cdot F_{amp\_ in} = U_{pre}`
which is the same as
:math:`\frac{U_{pre}}{H} = \frac{1}{\left( F_{sensor} \cdot F_{amp\_ in} \right)^{- 1} + F_{FB}}`
Close to the resonance frequency the influence of the sensor transfer
function disappears and the overall characteristics depends mainly on
:math:`F_{FB}`. This results in a flat frequency response of the sensor
system over the whole frequency band of interest.
Additionally the preamplifier electronics contains an output line driver
which provides an :math:`8 kHz` low-pass filter. The output buffer is able
to drive cables up to 70 m length.
.. figure:: /media/mfs-06e/preamplifier_of_mfs-06e.jpg
:width: 50%
:align: center
Preamplifier of MFS-06e
Transfer Function of MFS-06e
-------------------------------
The transfer function of the MFS-06e magnetometer is determined by the
transfer function of the preamplifier, the feedback electronics and the
sensor transfer function.
The theoretical overall transfer function is defined by the following
equations:
**a) CHOPPER ON**
:math:`F_{Sensor} = \frac{V_{output}}{H} = 0.8\frac{V}{nT} \cdot \frac{P_{1}}{1 + P_{1}} \cdot \frac{1}{1 + P_{2}} \cdot \frac{1}{1 + P_{4}}`
or normalized as we use it in our calibration files:
:math:`F_{on}(f) = \frac{ V_{output} }{H \enspace Hz} = 0.8 \frac{V}{nT} \cdot \frac{P_1}{1+P_1} \cdot \frac{1}{1+P_2} \cdot \frac{1}{1+P_4} \enspace / \enspace f`
**b) CHOPPER OFF**
adds a term :math:`P_3 = i \frac{f}{0.72 Hz}`
:math:`F_{Sensor} = \frac{V_{output}}{H} = 0.8\frac{V}{nT} \cdot \frac{P_{1}}{1 + P_{1}} \cdot \frac{1}{1 + P_{2}} \cdot \frac{P_{3}}{1 + P_{3}} \cdot \frac{1}{1 + P_{4}}`
or normalized as we use it in our calibration files:
:math:`F_{off}(f) = \frac{ V_{output} }{H \enspace Hz} = 0.8 \frac{V}{nT} \cdot \frac{P_1}{1+P_1} \cdot \frac{1}{1+P_2} \cdot \frac{P_3}{1+P_3} \cdot \frac{1}{1+P_4} \enspace / \enspace f`
with
:math:`P_{1} = i \cdot \frac{f}{4Hz}` ,
:math:`P_{2} = i \cdot \frac{f}{8192Hz}` ,
:math:`P_{3} = i \cdot \frac{f}{0.72Hz}` ,
:math:`P_{4} = i \cdot \frac{f}{28300Hz}`
This theoretical transfer function is only an approximation of the
real transfer function (approx. up to :math:`500 Hz` with Chopper On)
which is delivered by the calibration of the sensor. Each sensor is
delivered with a calibration file which has a 3 column ASCII format.
The left column represents the frequency, the middle one represents
the sensor sensitivity in :math:`\frac{V}{nT \cdot Hz}` and the right
one the phase in degree.
As it can be easily calculated from the equation above, for very low
frequencies the transfer function of the coil converges to :math:`\frac{0.2V}{nT \cdot Hz}`
in amplitude and to 90 degrees in phase. The calibration data which is
delivered along with the coil ends at its low end at :math:`f = 0.1 Hz`. The
amplitude can be taken as the given value at :math:`0.1 Hz` also for lower
frequencies. The phase value for very low frequencies :math:`<0.1Hz` can be
computed to
:math:`\varphi = atan\left( \frac{4Hz}{f} \right)` with :math:`f < 0.1Hz`
In addation to the delivered calibration file the sensor is equipped
with the calibration data stored on a chip inside the sensor. This
information will be read by the ADU-07e. Each time a data recording is
done this calibration data is stored along with the recording data.
Integrated Calibration Facility
-------------------------------------
The integrated calibration facility makes it easy for the user to
perform an online calibration or test of the magnetometer transfer
function. A differential test signal can simply be injected into the
inputs and is internally added to :math:`U_{pre}` without further
amplification as shown in Figure 0-1. A voltage on the input results in
a magnetic field according to
:math:`H = 4\frac{nT}{V} \cdot U_{cal}`
This makes it easy to calculate the resulting transfer function of the
magnetometer using the formula
:math:`F_{MFS - 06} = \frac{U_{out}}{U_{cal}} \cdot \frac{1}{4\frac{nT}{V} \cdot f}`
External magnetic field variations do not disturb the measurement if a
correlation analyser (e.g. Solartron 1250) is used. The max. allowed
signal amplitude on the calibration input is :math:`\pm 10V` but it has to be
considered that the sensor may be saturated at higher frequencies. For
example at :math:`10 Hz < f < 10kHz`. The maximum amplitude shoud not exceed
:math:`80mV`.
If the metronix ADU-07e is used as data logger the magnetometer
characteristics will be tested regularly as a part of the normal system
self test.
Calibration by Manufacturer
------------------------------
metronix takes special care of the initial calibration of all MFS-06e
magnetometers as part of the ISO 9001:2015 certified production process.
Tests have demonstrated an excellent long time stability of the transfer
function.
The calibration is performed in the "Magnetsrode" geomagnetic laboratory
which is operated by the Institute of Geophysics at the Technical
University of Braunschweig, mostly to calibrate space flight
magnetometers. It offers special environmental circumstances and has an
extremely low distortion level.
A large solenoid (l = 3.6 m; d = 30 cm) has been calibrated by a
reference sensor with an accuracy of better than ±0.2%. It is used to
generate a homogeneous magnetic field of known strength as input signal.
The input signal for the solenoid comes from a N4L PSM3750 phase
sensitive multimeter which is able to perform calculation of transfer
functions with a given statistical accuracy.
Each magnetometer is calibrated to a sensitivity
:math:`E = 0.2\frac{V}{nT \cdot Hz}`
at a frequency of 0.1 Hz.
A calibration file is generated in a frequency range between 0.1 Hz and
10 kHz. Lower frequency calibration is not required because the sensor
obeys the mathematical rules (theoretical transfer function with a very
high precision.
Table 0-1 gives an example of a calibration file delivered along with
the sensor. Note that not all calibration results are given here due to
limited space, gaps are marked by dots here.
Each magnetometer is shipped with the original calibration data set
which contains the measured values of amplitude and phase of the
transfer function over the specified frequency band.
The calibration file is split into 2 sections. The first section shows
the results with the chopper switched on (LF mode) whilst the second
section shows the results with the chopper amplifier switched off (HF
mode).
Figure 0-1 and Figure 0-2 show the plots of the calibration function of
MFS-06e Ser. #002.
.. figure:: /media/mfs-06e/Typical_sensitivity_calibration_curve_of_MFS-06e.jpg
:width: 80%
:align: center
Typical sensitivity calibration curve of MFS-06e (here Ser.#002)
.. figure:: /media/mfs-06e/Typical_phase_calibration_curve_of_MFS-06e.jpg
:width: 80%
:align: center
Typical phase calibration curve of MFS-06e (here Ser.#002)
.. code::
Calibration measurement with NumetriQ PSM 3750 - 0.1.100000.1.17
Metronix GmbH, Kocherstr. 3, 38120 Braunschweig
Magnetometer: MFS06e#591 Date: 15/05/28 Time: 11:36:13
FREQUENCY MAGNITUDE PHASE
Hz V/(nT*Hz) deg
Chopper On
+1.0000E-01 +1.9967E-01 +8.8543E+01
+1.2328E-01 +1.9970E-01 +8.8237E+01
+1.5199E-01 +1.9966E-01 +8.7859E+01
+1.8738E-01 +1.9950E-01 +8.7352E+01
. . .
. . .
+6.5793E+03 +8.9360E-05 -4.7482E+01
+8.1113E+03 +6.6694E-05 -5.1570E+01
+1.0000E+04 +5.0655E-05 -5.7744E+01
Chopper Off
+1.0000E+00 +1.8918E-01 +1.1134E+02
+1.2329E+00 +1.9561E-01 +1.0250E+02
+1.5199E+00 +2.0082E-01 +9.3069E+01
+1.8738E+00 +2.0047E-01 +8.3521E+01
. . .
. . .
+4.3288E+03 +1.6625E-04 -3.5537E+01
+5.3367E+03 +1.2352E-04 -4.2456E+01
+6.5793E+03 +8.9360E-05 -4.7556E+01
+8.1113E+03 +6.6678E-05 -5.1616E+01
+1.0000E+04 +5.0661E-05 -5.7762E+01
Example for a calibration file (the dots indicate that not all lines are shown here)
Sensor Noise
------------
In an electromagnetic measurement system special care has to be taken to
noise. The various sources of noise in the system can be referenced back
to an equivalent input noise voltage at the preamplifier input for
comparison purpose which is expressed in the equation
:math:`\sqrt{\frac{\overset{¯}{u^{2}}}{\Delta f}} \approx \sqrt{\frac{\overset{¯}{u_{amp}^{2}}}{\Delta f} + \frac{\overset{¯}{u_{R}^{2}}}{\Delta f} + \frac{\overset{¯}{i_{amp}^{2}}}{\Delta f} \cdot \left( \omega^{2}L^{2} \right)}`
with
.. csv-table::
:delim: |
:math:`\sqrt{\overset{¯}{u_{amp}^{2}}/\mathrm{\Delta}f}`|preamplifier noise voltage density (typ. :math:`1.6\leftrightarrow nV/\sqrt{Hz}`)
:math:`\sqrt{\overset{¯}{u_{R}^{2}}/\mathrm{\Delta}f}`|thermal noise of sensor resistance (typ. :math:`2.7nV/\sqrt{Hz}`)
:math:`\sqrt{\overset{¯}{i_{amp}^{2}}/\mathrm{\Delta}f}`|preamplifier noise current density (typ. :math:`10fA/\sqrt{Hz}`) @chopper off
To rereference this noise voltage back to the magnetic field the formula
:math:`\sqrt{\frac{\overset{¯}{H^{2}}}{\Delta f}} = \frac{\sqrt{\frac{\overset{¯}{u_{}^{2}}}{\Delta f}}}{E_{o} \cdot f} = \frac{1nT}{28.8\mu\;V/\sqrt{Hz} \cdot f} \cdot \sqrt{\frac{\overset{¯}{u_{}^{2}}}{\Delta f}}`
is used. These two equations show that the current noise is spectrally
flat whereas the voltage noise of the amplifier and the coil resistance
increase proportional with 1/f to low frequencies. For higher
frequencies it is possible to eliminate a part of the preamplifier noise
if the chopper path is switched off. This can be done with a pulse on
the HCHOP line.
Magnetometer noise is measured at metronix with an HP spectrum analyser.
To keep environmental noise away from the sensor the measurements are
done with the magnetometer in a multiple shielded Mu-metal chamber.
Additionally, the noise of the magnetometer is measured by a parallel
sensor test. The correlation between two parallel located sensors is
determined and by this means, in connection with the measured amplitude
spectra, the noise of the sensor can be computed.
.. figure:: /media/mfs-06e/typical_noise_chart_of_the_mfs-06e_in_comparison_with_the_natural_magnetic_field_variations_on_a_quiet_day.jpg
:width: 80%
:align: center
Typical Noise Chart of the MFS-06e in comparison with the natural magnetic field varitions on a quiet day
Installation of Magnetometers
-----------------------------
To avoid low frequency distortion due to mechanical vibrations of the
sensor it must be dug into the soil. If this is not done, significant
noise caused by wind may be created which can make a measurement
unusable. The z component magnetometer should be dug into the soil at
least to the amount of half of its size. In order to obtain optimum
results the free end of the sensor should be covered by a protection cap
like a plastic bucket.
Special care must be taken to the exact alignment of the magnetometer
tube. It’s bottom side (that one without the cable connector) must point
exactly to the corresponding (positive sensor) direction:
* **X magnetometer to the North**
* **Y magnetometer to the East**
* **Z magnetometer to the ground**
A positive flux change in the positive sensor direction will cause a
positive change in the output voltage.
Electrical Connection
^^^^^^^^^^^^^^^^^^^^^
All magnetometer cables from metronix are shielded twisted pair cables
which perform optimum protection against external distortion. Connectors
have best outdoor characteristics including water tightness.
Nevertheless, care should be taken to avoid intrusion of particles. Each
connector has a protection cap which can be removed by just pulling it
off. Please ensure that the expensive connectors are always protected by
the caps during assembling or disassembling of the MT system.
To connect a cable to a magnetometer rotate it to the coded position
(red dot to red dot), put connector into the input plug and lock it by
pushing it until it snaps in.
The MFS-06e can be directly connected to the ADU-07e data logger.
Due to the easy setup procedure of a metronix GMS-07 system, the
magnetometer cables simply have to be put into the corresponding
ADU-07 ports.
In case other custom electronics is used the production of a suitable
cable connection should be not too difficult according to the pin
assignment given below.
.. caution::
Special care must be taken with custom electronics to avoid a wrong use
of the power supply inputs! The magnetometer electronics may be damaged
immediately if the power is connected the wrong way!
.. note::
The Chopper On/Off Signal is a standard CMOS input. Low level (<0.5V)
will switch the chopper amplifier off. High level (>3.5V up to 13V) will
switch the chopper on. If you use the sensor with custom electronics,
make sure to switch the chopper line on and off with a delay of about
100ms or more in order to properly initialize the sensor.
Installation with ADU-07e
^^^^^^^^^^^^^^^^^^^^^^^^^
This chapter describes the setup of the MFS-06e in the field in
connection with the ADU-07e.
Standard 5-channel MT Setup
'''''''''''''''''''''''''''
Figure 0-1 illustrates the field setup of a five channel MT station.
Only a few components are required:
* ADU-07e with battery and GPS antenna
* 3 magnetometers like MFS-05, MFS-06e or MFS-07e
* 3 magnetometer cables
* 4 electric field probes
* 4 electric field cables
* 1 grounding rod + cable
* Field computer (temporarily - may be any ruggedized laptop)
.. figure:: /media/mfs-06e/typical_5_channel_mt_field_setup.jpg
:width: 80%
:align: center
Typical 5-channel MT field setup
Connection of the Sensors to the ADU-07e
''''''''''''''''''''''''''''''''''''''''
Now you can install the sensors:
1. Dig the four EFP-06 into the soil and connect them with the input of
the E-Field cable drum.
2. Connect the other end of the 50m E-cable with the appropriate input
terminals of the ADU-07e. The North-probe will be connected with
the terminal labelled "N" of the ADU-07e. In the same way the "S",
"E", "W" input terminals of the ADB are connected with the corresponding
probes. Make sure that the E-Field cables are unreeled completely and
the cable is not moving in the wind.
3. Stick-in the delivered grounding rod close to the ADU-07e and
connect it with the black GND-input clamp of the ADU-07e.
4. Connect one end of the magnetometer cables with the HX, HY resp.
HZ magnetometer. For this purpose first remove the magnetometer's
protection cap. Now push the end of the cable through the rubber
flap in the middle of the protection cap. After having it connected
with the socket properly, the magnetometer's protection cap is pushed
over the magnetometer's head again. Please note that the reel of the
magnetometer cable (if there is one) always should be placed near
the ADU-07e. The exact positioning and installation procedure of
the magnetometer is described below. It is very important to notice
the hints given there in order to obtain best results.
5. Connect the plugs on the other end of the magnetometer cables with
the corresponding input sockets on the ADU-07e i.e. the cable of
the HX sensor with the socket labelled "HX", the cable of the HY
sensor with the "HY" socket and the cable of the HZ sensor with
the "HZ" socket of the ADU-07e.
The correct direction of the sensors can be fixed by using a compass and
two sticks:
A field helper rams the first stick into the soil according to the
command of the other helper with the compass. The second stick is rammed
behind the first stick. The correct alignment is found when the needle
of the compass points to North for HX resp. East for HY and the sticks
as well as the ring and bead sights of the compass are in line.
The horizontal direction is balanced using a level. The exact vertical
position of the HZ-magnetometer can also be fixed by a level.
The magnetometers must be installed in a way that any movement of the
sensors due to micro-vibrations is avoided. Such motion of an induction
coil magnetometer in the stationary earth magnetic field would cause
significant artificial noise. For this reason the horizontal
magnetometers must be dug and covered by soil completely. The vertical
HZ-component should be dug-in to at least half of its length or better
to 4/5 of its length. An additional coverage of the HZ sensor by a
plastic bucket helps to reduce wind influences.
.. note::
The cables close to the magnetometers must be fixed in a way that they
cannot move in the wind!!
Pinout of Connector Socket
--------------------------
.. csv-table::
Pin-out of magnetometer socket
:delim: |
Socket 10-pole ODU MiniSnap G32KON-T10QJ00-000 Pin|Signal
1|+12V
2|-12V
3|H-Chop
4|Sensor GND
5|Cal Signal+
6|Cal Signal -
7|Input +
8|Input -
9|:math:`I^{2}C` SDA
10|:math:`I^{2}C` SCL
The picture below shows the front side of the socket or the rear
side of the corresponding plug with the solder cups.
.. image:: /media/mfs-10e/frontside_of_the_socket.jpg
:width: 20%
:align: center
You can order a suitable cable plug from Metronix or directly from the
manufacturer ODU in (`www.odu.de `__)
The part number of the plug is ODU Minisnap Series K
S22KON-T10MJG0-7000
You may also need a strain relief streeve ODU part.no.
702023205965060
.. csv-table::
Wiring list of magnetometer cable MFS-06e/07e to ADU-07e
:delim: |
**Target ODU MiniSnap Series K 10 pole**|**Origin ODU MiniSnap Series K 10 pole**|**Signal**|**Colour**|**Cat.**
1|1|+12V|white|\\ twist
9|9| SDATA|brown|/ ed
||||
3|3|HCHOP|green|\\ twist
4|4|GND|yellow|/ ed
||||
5|5|+CAL|grey|\\ twist
6|6|-CAL|pink|/ ed
||||
7|7|Signal out|blue|\\ twist
8|8|Signal Return|red|/ ed
||||
2|2|-12V|black|\\ twist
10|10|SCLK|violet|/ ed
||||
Case|Case|Screen||
Trouble Shooting
----------------
This chapter describes our experience to localise possible errors of the
system and methods how to fix them or get around it.
Parallel Sensor Test
^^^^^^^^^^^^^^^^^^^^
In order to check the functionality of the sensors it is a good idea to
perform a so called parallel sensor test. For this purpose 2 or more
magnetometers are positioned horizontally and parallel with a distance
of about 2 m from each other. Dig in the magnetometers. The electric
field lines are laid out in parallel and perpendicular to the magnetic
sensors. Use a single probe for each line (all together four of them).
Now you record time series. If everything works fine you must see well
correlated time series of the electric and the magnetic channels. A
noisy sensor can be found out by this method easily.
Check of Magnetometer Cable
^^^^^^^^^^^^^^^^^^^^^^^^^^^
The pin-out of the magnetometer cable is given in chapter 0. Check the
cable by using an Ohm-meter pin by pin according to the table. Also
check for damages of the cable´s isolation.
.. caution::
Never pull the sensor out of the soil on its cable because either the
cable connector or the sensor socket will be damaged by this procedure.
In Situ Measurement of Transfer Function
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Metronix provides a software tool which allows to check the sensor´s
transfer function in the field. This is achieved by a special joblist
running on the ADU-07e which records some data for about half an hour.
In course of this procedure test signals are fed into the calibration
coil of the magnetometer. The software reads and processes the data and
delivers the transfer function of the sensor as a result. You will find
the necessary software on the USB key delivered along with the ADU-07e
(subfolder software).
Noise Chart
-----------
The performance characteristics is shown here:
.. image:: /media/mfs-06e/MFS-06eNoisechart.jpg
:target: /media/mfs-06e/MFS-06eNoisechart.pdf
:width: 80%
:align: center
So, the chopper off recordings should cover the 32 Hz and the chopper on should start below.
Chopper on recordings naturally start at 512 Hz. And the chopper off 4kHz should be chosen long enough to reach 32Hz.
Continue to read :ref:`here `.