PPM operator manual

[Willy Bayot]

Option 1 supposes that the control box is at least one meter away from the sensor.
Our experiments have shown that the readings are disturbed if the GPS engine is closer.
However, these experiments have been conducted using another GPS engine than the one we intend to integrate in the box, it could be that this one was containing some magnetic material.

Willy

[BillA]

integrated GPS

Hi Willy

option 1 sounds good to me
looking forward to the 1st assembly photos

Bill

[Willy Bayot]

latest GPS option details

Bill,

We foresee now three distinct types of GPS option support in our system:
1. We provide an internal GPS engine fixed on the controller board under the lid of the control box.
2. We provide the same GPS engine but contained in a small, watertight box and connected to the control box through a data cable through an IP68-rated connector
3. Your own SIRF III- compatible GPS device to be connected to the same connector to the control box. We just provide the software driver option in the controller code.

Willy

[Willy Bayot]

Kevin,

The maximum length of the cable depends essentially to its electrical resistance. The voltage loss in the cable should not make the polarization current go down too much, otherwise the proton precession signal will be too weak to be measured.

A shielded cable with two 1mm diameter wires has a resistance of 0.042 ohm per cable meter (two times the wire length).
Our standard two coil sensor has a total resistance of 5 ohms. Under 12V, it takes a current of 12/5 = 2.4 Amps. With a current >= 2 Amps, we get a good SNR.

A cable of 20 m under 12V will give a current of 12V/ ( 5 ohms + 0.84 ohms) = 2.05 Amps which is good.
A cable of 40m under 12V will give a current of 12V/ ( 5 ohms + 1.68 ohms) = 1.8Amps which is good enough at sea since the level of noise is low there.
A cable of 100 m under 12V will give a current of 12V/ ( 5 ohms + 4.2 ohms) = 1.3 Amps--> really not enough
If you can find cables with 2mm diameter wire, the voltage loss would be much lower. It would only have a resistance of 0.01 ohm per cable meter. So, a cable of 100 m would only have a resistance of 1 ohm and a 12V battery would give you 2 Amps applied on our sensor of 5 ohms.

Willy

Willy, I am contemplating your unit for underwater surveys from my boat, can you advise the maximum length of cable that could be used between a tow-fish mounted sensor and the control head. Also, what cabling would you recommend?

Thanks, Kevin

[Willy Bayot]

Hi Bill,

We'll most probably use the Buccaneer series from Bulgin:
http://www.bulgin.co.uk/PDFs/CatNo82...ndard_2005.pdf

They are available at Digikey and are IP68 Rated (tested at 10m depth for 2 weeks).

Willy

[BillA]

connectors

I use AMP/Tyco circular connectors because they are on the G858, but the sensor connectors (3 coaxial + more pins) are mil spec; none are water resistant.

You might look at Conxall (pn 7282-6PG-300*), they have an o-ring that sets inside the male socket; the backsides would have to be potted.

Bill

[Willy Bayot]

about the new case: waterproof is GOOD, dust proof is even better
Is it not true that 'waterproof' automatically implies 'dust proof'?
- are you going to utilize water resistant connectors for the battery and sensor(s) ? (generally an o-ring within)
We'll see what is available at Digikey. Any idea?
- is the case large enough for a second set of boards for use as a gradiometer ? (only one with on-board GPS presumably, and only one control panel)
This specific NEMA box would not but there exists larger boxes in hte same series.
I do presume that a sensor housing will be available, even if hand fabricated,
what would the sensor weight be (nominally) ?
A double-coil sensor alone weights 1.6Kg.
so a gradiometer would be 2x that sensor weight, correct ? (plus fiberglass pole)
Yes
what is the recommended vertical spacing for the 2 sensors ?
You can use a vertical or an horizontal pole. It should be around 1.5 to 2meters long for undergorund surveys. However, it also depends on what targets you are looking for.
Another method to build a gradiometer configuration is to use two identical and separate PPM systems carried by two operators and walked along th esurvey lines together with the two sensors at constant distance.
Thanks Willy

Willy

This new case is for me much better than the titanium case and look more "Geophysical instrument" and it is very good for dust and moisture free
Alexis

[BillA]

re the proposal

about the new case: waterproof is GOOD, dust proof is even better
- are you going to utilize water resistant connectors for the battery and sensor(s) ? (generally an o-ring within)
- is the case large enough for a second set of boards for use as a gradiometer ? (only one with on-board GPS presumably, and only one control panel)

I do presume that a sensor housing will be available, even if hand fabricated,
what would the sensor weight be (nominally) ?
so a gradiometer would be 2x that sensor weight, correct ? (plus fiberglass pole)
what is the recommended vertical spacing for the 2 sensors ?

Thanks Willy

[Willy Bayot]

GPS and new enclosure

Hi,

We have decided to use a NEMA-type enclosure to get a better protection against the wet and salty environments. See attached, the picture of box we'll use.
We know that it is not as nice looking as the small round box shown before but it is also more roomy inside, more rigid and splash-proof. There will be a daughter board fixed in the inside of the cover and on which the LCD, the keypad, the SD card socket, the buzzer and the optional GPS engine will be fixed.
There will be no openings on the box. The SD card will be removable with the cover opened using its latches. The LCD screen will be viewed through the transparent cover. The key buttons will be protected under a rubber cap.

About the GPS option, we'll propose two distinct options:
1. A serial line (with a standard 9-pin DSUB connector) to any external SIRFIII-compatible GPS device. The DSUB connector will also provide one 5V power pin to power the GPS module. This option is software-only, it could be ordered at any time after shipping.
2. An internal GPS engine inside the control box and with its patch antenna facing up the cover of the box. This option should be ordered before shipping the whole system as it must be integrated by us inside the box.

Attached are also:
- the GPS option upgrade to the operator manual and
- the price proposal with the corresponding optional pricings.

Willy

[Willy Bayot]

if I am interpreting your answer correctly, . . . .
no, there is no GPS hardware included in the PPM
Yes, we'll propose an internal GPS module as an option. It will be integrated inside the electronic enclosure with its patch antenna facing up.
We'll probably use this one from USGlobalSat:
http://www.usglobalsat.com/download/46/em406a_ug.pdf

I would observe that the statement that the software "will support any GPS based on the SIRF III chip set" is not sufficient guidance (for me at least) to figure out how to do it. I have no earthly idea who uses that chip set.
A word of explanation about GPS applied to our PPM system.
The GPS host protocol universally supported by all modern GPS is the NMEA data stream and its ASCII-coded commands/responses.
We would have liked to support this protocol as well but it does not work in our specific case because there is no standard command to poll the fix readings when we can accept them (i.e. during polarization periods) without disturbing the weak precession signal.
The SIRFIII binary protocol is supporting this polling method and the SIRFIII chip set has many advantages:
1. Very sensitive, can even make a 3D fix inside buildings.
2. Supported by more and more commercial GPS devices, (most probably due to point 1.)
3. Support poll mode
4. Supports removal of the static navigation mode which returns constant fixes when the speed goes down too much; This is not acceptable for a survey made while walking. A normal walking speed triggers the static navigation mode.

We still want to propose an external GPS Option to those who already own a GPS (e.g. on a boat) or who need the GPS antenna to be located far from the electronic control box.
There are a number of GPS engines which can be used as external devices from USGlobalSat (with or without integrated patch antenna, supporting active external antennas,...)
Perhaps you could recommend specific GPS units ?
Then I would ask if their magnetic signature has been assessed wrt the PPM (heading errors) ?
These OEM GPS engines are just made of electronic boards and do not generate any sensible magnetic signature.
Bill

Look at the forum, I'll make the necessary formal annoucements and operator manual upgrades.

Willy

[BillA]

if I am interpreting your answer correctly, . . . .
no, there is no GPS hardware included in the PPM

I would observe that the statement that the software "will support any GPS based on the SIRF III chip set" is not sufficient guidance (for me at least) to figure out how to do it. I have no earthly idea who uses that chip set.

Perhaps you could recommend specific GPS units ?
Then I would ask if their magnetic signature has been assessed wrt the PPM (heading errors) ?

Bill

[Willy Bayot]

A small precision about GPS.
The GPS Option has not been described in the manual because it is still under tests but its specific code in the firmware has been written and tested. It will support any GPS based on the SIRF III chip set and will be priced as an optional software feature upgradable through internet.
When activated, the GPS is polled at each PPM reading and the fix data are integrated in the captured data record used as XY values in the grid.
The tests we still make now are to check if the serial data stream coming from the GPS does not disturb the weak signals we need to measure when using various type of GPS.

Willy

[Willy Bayot]

Hi Willy,
I figured you would answer my questions if I waited, and mostly you have.

Are you intending on integrating a GPS sensor/unit, and coupling the data stream to the software 'package' ? Notwithstanding the absolute inaccuracy involved, coordinates are useful - in my case essential.
YES
I would ask another question which doubtless was described in another of the numerous threads on this project, sorry if I missed it - a link would be fine.
Normally two sensors will provide a differential output, the typical gradiometer as an example. Your unit has two sensors yet a differential output is not available, another parallel instrument is required. What did I miss ?
Each instrument has a single sensor. A Differential PPM or a Gradiometer configurations are made by two identical and synchronized instruments capturing their reading separately on their own SD card. The post-processing system merges the two data stream, calculates the corrected field gradients and plots the results in 2D or 3D.
Thanks, Bill

Willy