PPM Mechanical assembly

[Willy Bayot]

This is a few pictures of the mechanical assembly of the PPM.

Willy

[Bill512]

very good !!!

[BillA]

hey Willy, looks fine indeed
thinking . . ., to free up that arm perhaps the box could be on the chest and the sensors supported off the hips somehow . . . (the hammerhead ??)

what are the variables associated with the sensors' elevation from the surface ? (in terms of other means to carry the sensors)

Bill

EDIT: actually several more questions,
The sensors are shown mounted normal to the shaft and parallel to the surface, is there not an optimal orientation given the location and direction of the traverse ?
In how many planes ?

[Willy Bayot]

hey Willy, looks fine indeed
thinking . . ., to free up that arm perhaps the box could be on the chest and the sensors supported off the hips somehow . . . (the hammerhead ??)


what are the variables associated with the sensors' elevation from the surface ? (in terms of other means to carry the sensors)

Bill

EDIT: actually several more questions,
The sensors are shown mounted normal to the shaft and parallel to the surface, is there not an optimal orientation given the location and direction of the traverse ?
In how many planes ?

It is a good idea. Could you please extend it a bit more?
We would be happy to find the best assembly which would make the work of the operator easier and comfortable for long survey sessions.

The sensor should be kept at least at 50cm away fromt he ground in order to avoid being disturbed by small specks of magnetic material at the surface.

In our western latitudes, the vertical vector of the magnetic field is the largest, thus, the orientation of a solenoid sensor changes the magnitude of the signal but only slightly. In my own surveys, I do not observe any change of sensitivity while walking around the field in any sensor orientation provide I keep the sensor more or less horizontal.
This could not be the case in the equator or in the polar regions.
Willy

[BillA]

a couple more questions Willy
- I am assuming that a traverse is straight with NO lateral swinging of the sensors . . .

sensors at 50cm min., is the target sensitivity appreciably decreased at 1m ?

if not, put the sensors in a fanny pack (or backpack) with the console on the chest

my area of interest is Bolivia (the magnetic Equator), so I would set the sensors vertically ?

Bill

[Willy Bayot]

a couple more questions Willy
- I am assuming that a traverse is straight with NO lateral swinging of the sensors . . .

sensors at 50cm min., is the target sensitivity appreciably decreased at 1m ?

if not, put the sensors in a fanny pack (or backpack) with the console on the chest

my area of interest is Bolivia (the magnetic Equator), so I would set the sensors vertically ?

Bill

Hi Bill,
No swinging indeed.
For weakly magnetic targets like archaeological structures, that could make a difference but for shallow or largely magnetic targets, that should be less important.
However, we have not yet really measured the influence of a close proximity of the sensor with the electronic box and its noise-generating processor.
We would then prefer to fix a mast to the backpack and fix the sensor at its top.

Yes, at the equator, the main magnetic vector of the magnetic field is horizontal. Since the axis of the coils should be set at 90° from it to get the highest signal magnitude, you should keep the sensor tube at vertical position.

Willy

[Willy Bayot]

a couple more questions Willy
- I am assuming that a traverse is straight with NO lateral swinging of the sensors . . .

sensors at 50cm min., is the target sensitivity appreciably decreased at 1m ?

if not, put the sensors in a fanny pack (or backpack) with the console on the chest

my area of interest is Bolivia (the magnetic Equator), so I would set the sensors vertically ?

Bill

An other method to carry PPM's is an horizontal stick carried with a belt. The sensor is fixed at one of its end and a counter-weigth at its other end.
That's the way I currently make my own surveys and I use the battery as counter-weigth.
However, for our new PPM, we plan to use a light LIPO battery which is not heavy enough. This battery will be fixed to the carrying stick at the level of the ankle.

Willy

[carthage]

Q and or suggesting.

Hi Willy,

It is great that your work is come a long way, and nice to see people around the world are waiting for you to give your green light that product is ready for them .
I have a question and can be a suggesting.
Would it be possible to make the sensor thinner and longer, that would provide a balance to its weight during scanning and that would make it easier to keep it // to the ground during search in the field and to store it too.

Regards
A.K

[Willy Bayot]

PPM assembly discussion

Hi Willy,

It is great that your work is come a long way, and nice to see people around the world are waiting for you to give your green light that product is ready for them .
I have a question and can be a suggesting.
Would it be possible to make the sensor thinner and longer, that would provide a balance to its weight during scanning and that would make it easier to keep it // to the ground during search in the field and to store it too.

Regards
A.K

Thank you for your comment and suggestion.
Ths is the whole subject of our current team discussions: i.e.
1. How do we package the sensor to easily and comfortably carry it with a single person?
2. What is the right compromise between low sensor weight and good SNR?

These aspects of the project are much easier to solve for underwater surveys as the boat carries the instrument and the batteries and the water carries the sensor. In fact, in that case, heavier sensor is better since it reduces the weigth of lead to be added to get the required depth.
Moreover, in the middle of a sea, we could expect a much lower level of noise. Thus, would not need any noise cancelling mechanism.

In our particular case, we have the choice between several noise-cancelling sensor coil configurations (axial coils or side-by-side coils) and fluid locations (coil-inside-fluid or fluid-inside-coil).
The selection of one of those options will condition the shape of the sensor container.
The axial coils configuration ends up with a longer, thinner sensor usually to be carried horizontally but its noise cancelling capabilities are less effective.
The side-by-side coils configuration needs a sensor container which is shorter and thicker and its noise cancelling properties are very effective.

We also have to consider the mechanical assembly used to carry the whole instrument.
The folding carrying stick and electronic box shown on my latest pictures have been entirely recuperated from the production model of an existing metal detector for which we own a rather large stock of mechanical parts.
However, this instrument configuration does not easily compensate the weigth of the sensor at the end of the carrying stick, thus, we need to reduce as much as possible the weigth of the sensor and the length of the carrying stick even using an chest-based harness as shown on the pictures.
This requires to use smaller, lighter sensor coils. We feel that the whole weight of the sensor container in that configuration should not be more than 1.5Kg. However, our current tests with two coils of 500gr set axially or side-by-side have shown that the amplification gain should be too high giving a less than optimal SNR in populated area.
A possible option to relieve the operator from the weight of the sensor is to put it on a small non-magnetic two-wheel carriage pushed or pulled by the operator. However, this is only possible on fields with a rather flat ground.

Another method to carry a PPM is the one I currently use in my own surveys with a prototype of our system. I have used a long stick (two meters) of aluminum horizontally carried with a shoulder-attached belt. The sensor is fixed at the forward end of the stick and the 12V Gel-cel battery fixed at the back end as counter-weight as it has abouth th esame weight as the sensor. In my own experience, this enables an operator to easily and comfortably carry an heavier sensor during long survey sessions.

A last option which is also possible and easy to implement is to carry the instrument on the chest, the battery on the belt and the sensor in a backpack. This option would be the most compact of all and would accept rather heavy sensors but we have not yet verified whether the closer proximity of the three main components of the instrument does not generate any disturbance of the signal quality.

We could possibly avoid to take any of those decisions ourselves and ship the instrument packaged a three separate packages:
1. The electronic box with its operator interface and grid storage
2. A full sensor with its cable to be connected to the electronic box through a proper connector.
3. The battery (in its container) with its cable to be connected to the electronic box through a proper connector. Added to this, a specific battery charger.
The assembly of the three elements together would then be left to the user the way he feels better for his particular usage.
We could then foresee two different kinds of sensor, one for ground surveys and one for underwater survey to be easily inserted inside a fish (thus, an axial configuration).

Any suggestion or comment from anybody would be welcome to help us in this project phase.

Willy

[Willy Bayot]

NB1:
Just note that my current sensors are side-by-side, fluid-inside-coil type and their total weight is 2Kg (two coils and fluid included). These give me full satisfaction for my real archaeological surveys.

NB2:
Remember, we are a team of electronic and software engineers, not mechanical engineers. If anybody out there can help us from his background and experience in this critical project phase, he would be very welcome.

Willy

[Willy Bayot]

Just an update of our progress related to the mechanical design of our PPM.

We have now decided to use a much simpler assembly than the one initially thought.
The box and its LIPO battery will be fixed to a non-magnetic chest plate hanging from two belts going over the shoulders. The same belts will carry the sensor at the level of the buttocks at the back of the operator.
This setup has been tested and was found to be the most comfortable, simplest and most flexible with the two hands free. It is also easy to transport.
The only constraint is that the operator carefully cleans up himself of all magnetic material like watch, knife, zippers made of steel, steel-protected shoes.... This clean-up process can be verified using the instrument itself by passing the sensor around the body and examine the potential field gradients it generates.
The sensor will be made of two coils fixed side-by-side with their axis kept horizontal and inserted inside a short external tube of 100mm of diameter for their mechanical protection.
Currently, this sensor works well with the fluid-inside-coil mode using small PVC bottles inserted inside each coil. This mode is the safest in terms of potential fluid leakage.
We know that the coil-inside-fluid mode (i.e. external tube completely filled with fluid) is logically able to generate a better signal since the volume of proton-rich fluid activated by the polarization is larger but it is also more prone to leakage.

The side-by-side coil configuration has proven to be much better in noise cancelling than the axial configuration used in underwater surveys. This noise cancelling is much more important in underground surveys as the noise level is higher than at sea.

We have designed the dimensions of the pair of coils to also be usable in axial configuration for their insertion inside a fish for underwater surveys. This could be an option of the instrument we would study later on.

Pictures of this setup will be published shortly on this forum.

Willy

[Willy Bayot]

Pictures of packaged PPM

Hi, This is two pictures of the latest packaging version. It shows the electronic box and the LIPO battery fixed on the chest plate through adjustable and disconnectable straps and belts and also shows the sensor carried at the back of the (here, young) operator through the same belts going over the shoulders.


This packaging has been successfully tested in the field and has shown a good confort. The total weight is only 3Kg shared between the front and the back parts.

As I said before, the only constraint is a thorough magnetic clean-up of the operator, head to shoes.

Willy

[Willy Bayot]

Hi,,
This is a survey of 45x20meters I made alone this morning in 20 minutes with the PPM in its latest packaging. This is an area around which we know there were some roman baths.
That was a delight compared to the mechanical assembly I used previously for my archaeological surveys (it was a long horizontal stick with the sensor at one side and the battery at the other side, carried from a belt passing over one shoulder).

You can clearly see the negative gradients around the survey area which are indications of fences or buried elements of fences but the structure in the middle (around 13,35) is not ferrous (it is a positive gradient while ferrous material makes it negative). We'll make some vertical digging or drilling later on to check what's there.
The signal was of the highest quality in spite of the fact that this survey was made in the backgarden of an old, empty house located in the middle of a group of inhabited houses.

For those who can read XLS files, I have joined a ZIP file containing the real data capture and several interesting plots.
The plot 's' is the standard deviation in nT's of the signal at each measurement. The real accuracy of the measurement is 1/10 of this sigma value. You can see a few higher values of sigma which is normal in inhabited area.
The plot 'm' is the magnitude of the amplified and filtered signal in mV
The plot 'd' is the exponential decay of the signal during measurement expressed in %.
The plot 'b' is the total value of the magnetic field vector.

Willy

[Willy Bayot]

Hi all memebers,

You have not heard much from us lately but we are actively working on the project.
We have now started our production process by looking for various suppliers and manufacturers to build the components of our instrument with a professional quality.
We are happy with the electronic sub-systems, i.e. making bare boards, buying components and assembling them.
However, we have difficulties to find manufacturers with reasonable quotes for the mechanical parts and assembly.
More specifically, we got quotes for the professional coil winding process which were much too high for our liking.
Our specs are still quite simple, two solenoids made of 11 layers of AWG18 magnet wire wound onto a kernel of 50mm diameter and 65mm long. That's it. We know that the copper wire itself is rather expensive but it just require less than 2Kg per sensor.
If anyone on this forum knows where we can enquire for this job, we would be very thankful.
Thanks,

Willy

[Willy Bayot]

Hi,

We have not got any quote from any professional coil winding company thus, we have decided to buy a coil winding machine and make the coils of our sensors ourselves.
We have now all the necessary information to be able to publish our price structure and start a small production series.

I'll open a new post on this forum to give the details of our offer.

Willy