PPM IV (GUI) Manual
Procedures
1. Power up procedure
1.1.
Connecting a Battery
The PPM
system is not supplied with a battery. Thus, you have to select and provide
your own battery. It must be a non-magnetic type of battery, usually, a
lead-acid 12V battery of a capacity of around 5AH. You must connect its red
pins on the red wire of the system cable and the blue pins on the blue wire.
1.2.
Inserting the SD Card
Normally,
the PPM is supplied with a SD Card already inserted in its slot. Open the cover
of the box and you will see its socket on the controller board attached to the
cover. The SD Card is removed by pushing and releasing it to unlock it from its
socket. In order to re-insert it, just push it up to the top of the socket; it
will then stay locked in.
1.3.
Connecting the Sensor
The sensor
is supplied with a cable and a connector. Insert the connector of the cable
into the corresponding connector of the box.
1.4.
Power up
Now, you
can power up the system by flipping its power switch. You will hear a small
beep and a window on the screen will show the message '
2. Exploring Window Structure
2.1.
Home Screen
The HOME
screen has two blue buttons (Grid and System) and an 'Expert' check indicator.
At the
bottom of the screen, there are two comment lines displaying the build
date/time stamps of the PPM and GUI firmware.
2.2.
System Screen
If you push
on the 'System' button, you will get the upper part of the System parameter
setup screen. This screen will allow setting the Operation Mode, the Local B
field value and the amplifier Gain.
All these parameters are set at a default value in factory. At this point, do
not change any of them.
You will
also see a changing value 'NL'. This is the Ambient Noise Level expressed in mV as captured by the sensor without
any polarization and measured by the system. This gives an indication of the
local human-generated noise. It must be
below 50mV in normal site conditions. We shall use this indication later in the
procedure.
Push now on
the HOME button to return to the Home screen.
2.3.
Expert System Screen
Press the
'Expert' check button to activate it and press again on the 'System' button.
This will
display the whole system parameter screen.
The bottom half of the screen shows less often modified parameters.
The Polarization Period bar gives
the reading rhythm expressed in seconds; it is set by default to one second
(maximum rhythm of one reading per second).
The Polarization Duration' bar gives
the duration of the polarization current. Its default value of 650ms is to be
left as-is.
The 'Delay' is the delay inserted
after the end of the polarization and the start of the measurement period. Keep
it with that value.
The ''Gradient Threshold' is the
threshold of field gradient over which an aural warning is sounded.
There is
also an 'FFT' button (used in
3. Tuning the sensor) and an 'Update'
button (used in 7 and 8. Upgrading firmware).
Go back
Home again.
2.4.
Grid Screen
Push on the
'Grid' button of the Home screen.
You then
see the 'Grid' Screen.
To the left
of the screen, there is a list of grid file names present on the SD Card. At
initial installation, you should see only a few of them, mostly the ones which
were generated during the factory testing of the system. They all start with
'GD' followed by a date 'mmdd' followed by an index number in the same day.
If the list
is longer than the height of the screen, the last entry is 'More...'. Push on this entry to display the next entries.
The current
grid name is also displayed at the top of the screen, on the right of the first
list entry. This is the name which will be created for the next session.
This name
may be modified by first pressing the 'Bck' button
and then, pushing the numeric keys as required.
The row of
buttons at the bottom of the screen is the control panel of the grid files.
'Open' will open the currently selected file for
review.
'Erase' will delete the currently selected file.
'Create' will create a new file with the name as set at
the top of the screen.
'Home' returns to the Home screen. Push on it now.
3. Tuning the Sensor
3.1.
Introduction
The sensor
tuning process sets the sensor to resonate at the average local precession
frequency by connecting proper valued capacitors in parallel to the coils of
the sensor.
A tuned
sensor gives two important advantages to the whole PPM system.
It acts as
a band pass filter filtering out the ambient noise of different frequencies and
amplifies the signals with the center (tuned) frequency.
Before
doing the tuning, we must first measure or evaluate the average local
precession frequency.
There are
some Web sites which give the approximate precession frequency given the GPS
fix of the local region where the surveys have to be executed. However, we have
provided an frequency measurement system integrated in
the PPM and based on an FFT algorithm which give a much more precise local
frequency value.
Knowing
that frequency value (from one method or the other) and the inductance of the
sensor, we can then calculate the capacitance to be put in parallel to the coil
in order to make the sensor to resonate at that frequency.
3.2.
Tuning Caps & DIP switch
The tuning
caps are given as a binary series of sequentially increasing cap values set in
or out of circuit by a 8 position DIP switch.
The binary
series is as follows:
|
Pos1 Pos2 Pos3 Pos4 Pos5 Pos6 Pos7 Pos8 |
328nF 164nF 82nF 47nF 22nF 10nF 4.7nF 830nF |
The FFT
process will give the values to be set on each position like for instance ‘01000110’. This means setting pos 2, pos 6 and pos 7 to ON (switch position
pushed down to the left) and all the rest to OFF (pushed down to the right).
Position 1
is the switch closer to the border of the board.
3.3.
Starting the Tuning Process
- Set all the DIP switch
positions to OFF (pushed down to the right)
- Go to a spot where you think
there are not too much human-generated electro-magnetic activities,
certainly out of any building with power supplies. That can be a back
garden or a recreation park.
- Put the sensor in horizontal
position and oriented to the East/West axis.
- Clean your body from any object
made of magnetic material (iron, steel, nickel).
- Power on the PPM
- Set the ‘Expert’ Check
Indicator and push on the System button.
- The NL value displayed and
refreshed every second on the System screen should not be much higher than
30mV. If it is not, then, this spot is probably not well selected. In that
case, you should try another spot.
- Push on the FFT button
- The screen blanks out for a few
seconds and you must hear a sound three times in a row; the FFT process is
actually doing three successive polarization and FFT measurements.
- After this period, the screen
comes back ON and re-displays the system parameter screen with the Base B
value set and more indications at its bottom half.
- Three precession frequencies
expressed in nT with the corresponding tuning
capacitance
- The average capacitance to be
set.
- A list of up to eight DIP
switch setting.
- One of the settings of the list
should be the best value to tune the sensor. Take a note of those but
there is also an ASCII-coded file recorded on the SD Card which gives the
same indications. Its file name starts with FR and its file extension is
TXT. You could take the card out and look at it on a PC.
- This is an example of such a
file (FR080302.TXT)
$TB
48384nT=326nF
$TB
48384nT=326nF
$TB
48384nT=326nF
$TC SET:326nF
$TD
01110110
$TD
01111000
$TD
01111010
$TD
01111100
$TD
01111110
$TD
10000000
$TD
10000010
$TD
10000100
$END
- You can see that the three FFT
attempts gave the same result, this means that
the spot was well selected.
3.4.
Setting the DIP switch positions
In
principle, the DIP switch position which will probably be the best will be one
in the middle of the list.
- Power OFF the system.
- Try first this one (on the
above example file, ‘01111100’) and proceed to the next point of the
procedure to execute a first static session.
4. Executing a Static Session
4.1.
Starting Session
- On the Home screen, push on the
System button.
- Check that the selected Op Mode
is ‘Static’. If not, Select it and push on the ‘SET’ button.
- Return to the Home screen.
- On the Home screen, push on the
Grid button.
- Push on the Create button, you
will be requested for a confirmation to create a file whose name is
displayed. Press OK.
- Now, you see the SURVEY screen.
- Press the ‘Start’ button
- The system starts polarizing,
measuring and displaying the local B field values every second.
- The B value is the absolute
precession frequency expressed in nT.
- The M value is the signal
magnitude expressed in mV. Higher is better.
- The S value is the Sigma
(Standard Deviation) giving an indication of the quality of the result.
Lower is better.
- The V value is the battery
voltage at the end of each polarization period (thus, under stress).
- The G value is the field
gradient in nT (signed difference between
consecutive readings)
- There is also a shifting bar
chart displaying the variations of the G value over time.
- Look more specifically at the S
and M values.
- After a few readings,
temporarily halt the repetitive readings by pressing the ‘Pause’ button.
- Take note of the S and M values
you have observed.
- Open the box cover and set
another DIP switch setting.
- Push on the ‘Resume’ button and
look again on the S and M values.
- Loop on these last 5 points of
the procedure until you have detected the position which gives you the
lowest S value (usually around 1 or 2 and certainly less than 10) and an M
value over 100. This is your best tuning setting.
- Stop the session by pressing
the ‘Stop’ button
- Now, with the best tuning
setting, start a new session on a new grid file (its index will
automatically be increased by one) and let it run for a few minutes.
During this test, avoid going close to the sensor. This static test will
confirm your tuning and will give you the dynamic behavior of the local
magnetic field over a period of a few minutes.
4.2.
Studying the result file
This is an
extract of such a file captured in my own office (not the best place to make
this test but you still see that the results are not too bad when the sensor is
well tuned)
SESSION:GD080610, 50mS,
650mS,160x,48165nT,1000mS,255
# 13 48177.6 4.1 357 11.04
# 23 48183.3 4.6 328 11.02
# 33 48178.8 4.4 307 11.02
# 43 48174.1 5.1 330 11.01
# 53 48177.3 4.3 365 11.01
# 63 48178.0 3.7 371 11.01
# 73 48171.5 3.4 409 11.01
# 83 48171.1 4.3 441 11.01
# 93 48170.3 3.5 387 11.01
The first
line gives the main system parameter values:
- Grid file name
- Delay
- Polarization Duration
- Amplifier Gain
- Base B
- Polarization period in msec (i.e. one per second)
- Gradient Filter
The next
lines are the reading results:
- Time stamps expressed in 1/10
second
- Absolute B field in nT
- S value
- M value
- Battery Voltage value
In normal
conditions of a magnetically-quiet environment, you should see the B values not
varying by more than a few nT
between consecutive readings. If a car has passed by at a few tens of meters,
you should see a large bump in the plot of B.
5. Executing a Multi-line Survey
Session
5.1.
Surveying Procedures
5.1.1.
Survey
Field evaluation Procedure
- If this is the first experiment
in that particular region, check the value of the local B field and the
noise/Spike/magnetic disturbance levels by running the FFT until you get
three consistent B field values. In that case, the $SB parameter has been
automatically set to the right value on the SD Card.
- Fine adjustment of the tuning
(minimize S and maximize M) at a fixed station in the middle of the area
to be surveyed. No problem to flip the DIP switches during the repetitive
polarization cycles.
- Set the Single Station operation mode and make a long traverse on the
two diagonals of the grid while observing the sigma, magnitude and field
gradient. By looking at the whole captured data, you can evaluate the
limits of B field values and check that the tuning is not on the 'edge of
stability' for the whole area.
5.1.2.
Survey
Procedure
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The surveys are usually made with a grid line separation of one meter and a length of
maximum
We measure the exact length of a survey line with a decameter, say L=50m. On each side
of the rectangular grid, we
pull a line (W1,W2) with a knot every meters or a
decameter. We initially plant poles with visible flag F1 and F2 on points 0,1 and L,0
That’s all for the site preparation.
·
Starting from one corner of the
grid (0,0), we trigger the
instrument to start its repetitive readings (menu : Start Session) and
we start a slow straight walking at a regular pace while visually aiming at flag
F2.
·
When arriving at flag F2, we
interrupt the readings (OK key).
·
We move the flag F2 to point
L,2
·
We go to point L,1 and resume the readings (OK key) slowly walking straight
at a regular pace while aiming at flag F1.
·
When arriving at flag F1, we
interrupt the readings (OK key).
·
We move the flag F1 to point
0,3
·
We go to point 0,2 and resume the readings (OK key) slowly walking straight
at a regular pace while aiming at flag F2.
And so on.
Note that the walking pace should be as regular as possible
for each line but it is not critical that the walking paces are the same for
all the lines.
The result of this survey is a sequence of survey line readings going in
zigzag mode.
5.2.
Reviewing Grid file
A captured
grid file can be reviewed by selecting its file name in the GRID screen and
pushing on the OPEN button. After confirmation, you get the SURVEY screen
displayed and you push on the Start button. There is a popup screen showing
that the grid is being loaded, then, the bar graph shows the end part of the
survey.
- If you touch one of the bars,
its field gradient will be displayed in the G field and its coordinates
will be displayed as well.
- If this was a raw survey file made in multi-line
mode, you will get the Row number (R) and the
- If the survey file was a GGxxxx
file(i.e. result of post-processing), you will get the
C as the precise coordinate of the point.
- If the survey file was made in GPS mode, you
will get the long/lat of the point.
- In order to see the previous
segments of the session on the bar graph, put your finger in the middle of
the screen and shift it to the right. The bar graph will move right and
you will see another segment on the session. If you want the bar graph to
shift to the left, move your finger to the left.
5.3.
Post-Processing and Plotting Survey Grid
Review
these procedures in Chapter 9 of the operator manual on the web site.
6. Executing a GPS-based Session
The
required accuracy of GPS fixes of PPM readings is relative and depends on the
work to be achieved:
- For underground surveys in fair
and rather flat ground where a rectangular grid of reasonable dimensions (say,
less than 50x50m) made of several parallel survey lines can be clearly
delimited for a single survey session, a single GPS is most probably not
accurate enough. However, in that particular case, the location of two opposite
corners of the grid can be defined by two GPS readings using a commercial GPS
unit or relative to a well-known fixed physical reference point (to be able to
come back to it later on), then, the survey itself could be made line by line
with a fixed separation of around 1 meter.
-
For single line surveys (as at sea
from a boat or in a deep forest or in a desert looking for meteorites from a
vehicle), what is needed is a continuous log of both PPM and GPS readings
during the survey followed by a study of the track and a localization of
potential targets over the survey line. In that particular case, an accuracy of
5 meters for the GPS fixes is enough to be able to go back later where the
potential targets have been detected during the post-processing.
It means that, except for professional applications requiring an ABSOLUTE
precision in the GPS fixes, most types of PPM surveys can be made with a single
commercial GPS and still give very satisfying practical results.
The
GPS chip we integrate in the PPM system is based on the SIRFIII Chip set and it
is more sensitive than most of the commercial GPS units. It is able to use up
to 20 Satellites and the experience showed that most of the surveys were made
with 9 to 10 satellites in view at a time when being in open countryside. This
gives a high fix precision evaluated to the meter range(HDOP
<= 1).
6.1.
Surveying Procedures
- In order to make GPS-based
surveys, there must be two conditions met:
- The system parameter $GO needs to be set
either to '$GO Y' or '$GO U'. The first option generates GPS fixes
expressed in Decimal Degrees and the second option generates the GPS
fixes expressed in UTM units (i.e. in meters). This parameter is not
accessible on the GUI menu system, it needs to
be set using a text editor on a PC on the GLOBAL_P.TXT file on the SD
Card.
- The Operation Mode must be set
to 'GPS'. This is set on the upper left of the System screen as a radio
button. After this setting, push on the SET button to record this value
on the SD Card and power OFF. At the next
- Go to the survey site and power
ON the system. If it was left without power for some time, the GPS will
make its 'Cold Start' procedure which will take possibly one or two
minutes to complete. If you start a session before the GPS is ready, you
will get a screen message asking to wait until the first fix is ready and
showing the number of Satellites in View (SV:x).
In that case, just wait until this message disappears and the normal
latitude/Longitude values are displayed. If the system was left without
power for a short period of time, the GPS chip will still have kept the
knowledge of its last location in its super-cap and will just make a 'Warm
Start' which is much shorter in time.
- Observe the H values displayed
at the right of the longitudes. This is the HDOP (Horizontal Dilution Of Precision). In order to get the most precise GPS
fixes, you must wait until the H values are 1 or less. This will not
happen immediately, it will possibly take a few more minutes before the
GPS has synchronized to enough satellites. The HDOP will only be small if
the number of satellites is high (about 8 or 9) and those are sufficiently
separated in the sky to enable the GPS to calculate precise fixes. When visible GPS satellites are close together in the sky,
the geometry is said to be weak and the Dilution Of Precision (DOP) value
is high; when far apart, the geometry is strong and the DOP value is low.
Thus a low DOP value represents a better GPS positional accuracy due to
the wider angular separation between the satellites used to calculate a
GPS unit's position.
Note: With an HDOP <= 1 and SV
>= 7, one can expect an average global fix precision of less than one meter. In full open country
or at sea, SIRFIII GPS devices
will usually give that quality of fixes or even better. This range of precision
is valid for the PPM surveys
over wide area where a GPS support is needed (e.g. underwater surveys).
- When the HDOP value is low
enough, start a GPS-based session while leaving the sensor at a fixed
position and let the session run for a few minutes. Then, review the file
and look at the variations of the B field. The G, S and H values should
stay very low.
- Now, you are ready to start
your real survey session.
- If you need to survey an area
where the human electro-magnetic activities generate large artificial
field variations in the underground and you want to detect deep and
relatively small targets, you will need to make a differential survey.
With two GPS-based PPM instruments, this is easy. You just start a session
with a PPM located in the vicinity of the survey area and you leave it there
for the whole duration of the survey session. You use a second PPM to make
the real survey session walking around this area. At the end of the
session, you stop the session on the two PPM's
(on the mobile PPM first) and you can then go to the Post-processing step.
6.2.
Reviewing Grid file
See 5.2. of this document.
6.3.
Post-Processing GPS-based survey files
The GNUPLOT
screen displays two GPS-related tabs, 'GPS m+b' and
'GPS m'.
- You push on the 'GPS m' tab to
post-process a survey file made with a single mobile PPM. This process
will just filter out the bad readings (S > 15) from the file and
generate a .GRID file with the same name and same format as the input grid
file.
- You push on the 'GPS m+b' tab to post-process a survey file made with a
mobile and a fixed PPM units. This process will merge the two data stream
based on their UTC values, filter out the bad readings (S > 15) on the
fixed and on the mobile stations and generate a .GRID file with the same
name as the mobile file. This is a sample of such a file:
$ 4.4461083
50.5075188 15.9 48451.0 3.9 163 48466.9 1.4 275
$
4.4461088 50.5075264 16.2 48451.0 3.9 163 48467.2 1.3 257
$
4.4461112 50.5075302 16.7 48451.0 3.9 163 48467.7 1.6 246
$
4.4461074 50.5075302 9.5 48451.0 3.9 163 48460.5 1.4 244
$
4.4461098 50.5075340 9.2 48451.0 3.9 163 48460.2 1.2 290
$
4.4461122 50.5075340 11.4 48451.0 3.9 163 48462.4 1.1 324
$
4.4461126 50.5075340 13.4 48451.0 3.9 163 48464.4 1.5 288
$
4.4461126 50.5075302 12.5 48451.0 3.9 163 48463.5 1.6 283
$
4.4461126 50.5075302 11.4 48451.0 3.9 163 48462.4 1.2 295
The field1 and field 2 are the corrected
long/lat,
The field 3 is the delta B between
corresponding readings
The fields 4,5 and 6
are the B,S and M of the fixed PPM
The fields 7,8 and 9
are the B,S and M of the mobile PPM
6.4.
Plotting Survey Grid
GPS-based
sessions may be made as a linear survey or a grid survey:
- Linear Survey.
This type of survey session is made as a single
line of readings without attempting to cover a specific and delimited surface
on the ground. This type of survey just requires a 1D plotting given either by
the grid review bar graph on the PPM itself or the same plotting made by simple
tools like Excel. The field gradients generated by potential targets are very
easily located from their corresponding long/lat fixes.
- Grid Survey.
This type of survey session is made by making a
multi-line grid attempting to cover as much as possible a delimited surface in
order to plot it in 2D or 3D. This is equivalent to the multi-line surveys
already described in this document but using the long/lat coordinates rather
than regularly-spaced row and columns. This type of survey requires a gridding process to spread the reading points over a
regular grid. This process is provided by programs like Surfer using various gridding algorithms.
7. Upgrading PPM Firmware
The
firmware files to be loaded in the PPM controller have an extension 'FWP'.
This file
should first be copied on the SD Card and it should be the only file on it with
extension 'FWP'. Then, power the system normally, check the EXPERT and press
the SYSTEM button on the HOME screen.
On the
bottom right of the expert screen, click on the 'Update' button to get the
firmware upgrade/update screen.
There,
click on the 'Update PPM' button. This button will rename as 'Updating...'. Now, be patient during the upload process which will take
up to one minute. At the end of this process, the system will reset with a
power down and power up of the GUI. Note now the new PPM build date at the
bottom of the HOME screen.
8. Upgrading GUI Firmware
The
firmware files to be loaded in the PPM controller have an extension 'FWG'.
This file
should first be copied on the SD Card and it should be the only file on it with
extension 'FWG'. Then, power the system normally, check the EXPERT and press
the SYSTEM button on the HOME screen.
On the
bottom right of the expert screen, click on the 'Update' button to get the
firmware upgrade/update screen.
There,
click on the 'Update GUI' button. This button will rename as 'Updating...'. Now, be patient during the upload process which will take
up to one minute. At the end of this process, the system will trigger a power
down and power up of the GUI. Note now the new GUI build date at the bottom of
the HOME screen.