Archaeology Resistivity Meter

Interesting ideas so far.  I meant to chime in earlier, but things have been pretty busy for me lately (building a deck and entertaining my Grandchildren again).

Several years ago, I was asked to sit in with some friends of my sister that work at a geotech company.  They were looking to build impedance measurement devices for soil surveys.  I came across this amazing looking chip from Analog Devices that looked like a great way to measure impedance (including a complex component).

Here is a snippet from the specification:

The AD5934 is a high precision impedance converter system solution that combines an on-board frequency generator with a 12-bit, 250 kSPS, analog-to-digital converter (ADC). The frequency generator allows an external complex impedance to be excited with a known frequency. The response signal from the impedance is sampled by the on-board ADC and a discrete Fourier transform (DFT) is processed by an on-board DSP engine. The DFT algorithm returns a real (R) and imaginary (I) data-word at each output frequency.Once calibrated, the magnitude of the impedance and relative phase of the impedance at each frequency point along the sweep is easily calculated using the following two equations:Magnitude = 22IR+Phase = tan−1(I/R) A similar device, available from Analog Devices, Inc., is the AD5933, which is a 2.7 V to 5.5 V, 1 MSPS, 12-bit impedance converter, with an internal temperature sensor, available in a  16-lead SSOP.

This might be of some help in your planning.

Good luck and let me know if you need any help on this project.

Hi Gene,

It's a super-interesting chip, I was keen to use it a few years ago for plant soil purposes, and for hydroponics - to try to see if the soil or liquid has nutrients. The idea being to have a signature of known good soil or water by sweeping through the spectrum. I never got to try it though sadly, the project moved on to something else.

It was felt that it could have had a lot of merit because then you could publish the signature, so others could try to replicate a yield (it wasn't going to be for farmers, more for home use), and to not waste nutrient. But, I have no idea in practice if the result would have been usable, or too inconsistent/variable.

I wish I'd done some work on it at the time, since it could have been useful for other purposes too.

The proposed design so far is one half of the impedance measuring system, but with digital processing. In theory it could be converted to an impedance measuring system with no additional hardware change, just a software upgrade, since the frequency will be know, and there will be some sync pulse from the FPGA, we just need to internally multiply with a 90 degree out of phase signal from that sync pulse too.

Dear All,

I have been following this thread and have some concerns about some of the comments.

To give an illustrative example.:-

If you want to design a chair most designs would look similar four legs, padded seat etc. The height would be one of the recommended "preferred" heights and it would have to meet legal requirements for strength and flammability. Given this information, most of us would sketch out similar designs. If one of our designs looked like the "Barcelona Chair" (designed by Mies van der Rohe and Lilly Reich) we should expect legal letters for design theft within a few months of putting them on sale.

I worked for a company that received such a letter and we were outraged that someone would lay claim to our work. After hours of work with our legal advisor we were shocked to discover how difficult it was to prove ownership of our work. Even having an RS catalogue (when they sent print editions out) was enough to suggest that we had the competitors information prior to our design and could have knowingly, or unknowingly, copied it. For the past three years I have been working on what BREXIT and trading on what World Trade Organisation (WTO) terms would mean for us. Its not so much 'WTO' as 'WTF' some of the examples are beyond belief.

For example:-

An American company designed and manufactured Multi meters and imported them into the USA. The meters were impounded by US Customs because a second US Company had convinced them that the colour of the faceplate was synonymous with their product. They had to pay to have them destroyed. The cost of a few weeks storage would have been more than the cost of the shipment and legal costs would have exceeded that within hours.

Many companies are now becoming aware of the value (or at least the cost) of their Intellectual Property (IP) and are willing to protect it. Phrases like "Product X does it this way", "I have downloaded their product information", "They have wired this way" or "We should not do it the way they did" are enough to cast doubt on the originality of your design. I am not even sure that the original magazine articles are not protected by copyright etc.

The Rolling Stones' legal team have written to D. Trump to "Demand" that he stops using their music - he must have bought a CD (or vinyl) but how he can use it is still controlled by the copyright owner.

In short, and probably too late, make sure you can prove the work that you "Open Source" is ALL your own work.

Paul D

In this case the project was initiated by a request from Mr MacDonald to address specific deficiencies – cost and the user interface.

There’s absolutely nothing wrong with a theoretical project, or the entry in a ‘show us a novel way to use XYZ chip’. Similarly there’s nothing wrong with folk throwing ideas because they may spark someone else’s thoughts.

There’s no doubt one could build a mousetrap controlled by an iPad or a Cray – but would it work any better? And would it be suitable to leave in a dark corner of an infrequently-visited room in the house, where it sometimes gets damp and occasionally someone with two legs accidentally stands on the trap? And why not replace the spring with a stepper-motor – that way it could be self-arming (ignoring the fact that a stepper-motor driven arm would have difficulty closing quickly enough before the mouse had walked away again) and yes, it would be multi-purpose, it could be used as a nut-cracker as well.

There’s nothing wrong with a multi-purpose solution – but just remember that a pair of pliers or mole-grips or a Stillson-wrench never does as good a job as a spanner of the correct size.

Dave

To add a little to the remarks from Shabaz and Dave,

The EPE design uses a synchronous rectifier and averages cycles using a switchable time constant of 1, 0.1 or 0.01 seconds.

The Geoscan research RM85 uses a phase sensitive detector (according to its manual) but doesn't say how it's implemented.

The Frobisher doesn't say.

The design approach we have been discussing can operate in all these modes (and others too).

The rationale behind the design is:

Since any instrument will need box, battery, connectors, pcb, controls, display, input and output amps and a processor

- probably costing between £100 and £180, depending on the display

then we may as well spend £30 on the FPGA, ADC and processor and DAC and have all possible options open, rather than £5 and box ourselves in.

This (I hope) makes the project attractive to the largest possible audience, since it offers the opportunity to do some reasonably state of the art electronics

while still offering a useful end result for several applications.

From my point of view there is no interest at all in working on a clone or component update of an old and limited design.

I hope to bring something new and improved to the party -  this is an open source hardware and software effort - so it's open to anyone to tweak, copy, build whatever.

MK

Interesting comments Paul,

Since this is open source with no commercial plans I'm not (very) bothered.

I have instinctively avoided linking or posting extracts of manuals etc and based on your comments I shall definitely avoid doing so.

If any one wants to sue me on the basis that it might enhance my professional reputation at their expense - bring it on

(or maybe they'll sue me for mentioning them in the same post as my own ideas )

More seriously, I feel that it's a positive good to society to seed the world with as much open source IP as possible so that

it becomes harder for companies and IP predators to make the kind of crazy claims they do.

So here's my stake in the ground:

What I claim is a thing for measuring stuff that uses an ADC, a DAC and a processor which might measure the stuff using a software phase sensitive detector or might not.

Thanks.

MK

You are confusing Apple and Microsoft et.al. with small companies and individuals who have invested their time and money (and their house or children's school fund) to produce stuff.

Even Apple and Microsoft et.al. deserve some protection - or who would decide who gets protection and who doesn't?

Even if you "Give" it away you could still get a legal letter - Farnell/Element14 would disappear it to the distance and let you worry about it.

You can "Open Source" your work but not the work of others.

Paul D

Re Mike and Paul’s comments:

Agree that there is a danger in attempting to clone or even reverse-engineer another design, especially if the actual task and domain are imperfectly understood.

I would absolutely advocate not trying to ‘improve’ the EPE designs as, irrespective of copyright issues, they were constrained by components and techniques available at that time.

What is needed is to understand the needs, possibly then some form of gap and opportunity analysis, and then design an exciting instrument that is usable, which potentially could be constructed by amateurs.

Dave

paul_d_arch  wrote:

 

 

For example:-

An American company designed and manufactured Multi meters and imported them into the USA. The meters were impounded by US Customs because a second US Company had convinced them that the colour of the faceplate was synonymous with their product. They had to pay to have them destroyed. The cost of a few weeks storage would have been more than the cost of the shipment and legal costs would have ex...

 

 

Fluke has trade marked the grey-and-yellow look and feel for handheld instruments in the USA.

Either adafruit or sparkfun (I forgot which of the 2) imported meters from China that were designed to closely mimick Fluke's look&feel.

Thats should not be a Ooops. Importing goods that violate a standing trade mark is not allowed since long time.

I the symposium I was at didn't say that the look and feel was a registered trademark (or more likely, I didn't remember).

It's a minefield. I always say respect the rights of others as you hope they would respect yours. The pain always occurs later and the delay always magnifies the expense.

I've consider it to be "bad manners" to copy the work of others. How do you know you are copying the best, or even good stuff?

The companies referred to don't seem big enough to aggressively protect their work (unlike Apple et. al.) but that doesn't seem to be a reason to rip off their ideas/products when you can do it yourself  - if you are willing to do the work

Paul D   

Yes, the old joke is - "if you want to go there, you shouldn't have started from here"

The physics hasn't changed but the technology we have has.

Paul D

Here is the TM: Trademark Status & Document Retrieval

The mark consists of the colors dark gray and yellow as applied to the goods.

For: Electronic test and measuring instruments and devices, and portable electronic test tools, namely, digital multimeters

There's also a drawing that shows the location of the two colours on a handheld device.

It was sparkfun. They communicated very openly about the situation: https://www.sparkfun.com/news/1430

Here is the TM: Trademark Status & Document Retrieval

The mark consists of the colors dark gray and yellow as applied to the goods.

For: Electronic test and measuring instruments and devices, and portable electronic test tools, namely, digital multimeters

There's also a drawing that shows the location of the two colours on a handheld device.

It was sparkfun. They communicated very openly about the situation: https://www.sparkfun.com/news/1430

Jan,

Thanks for the link. My original post was a third-hand retelling of this. It was a long day and I should have been paying closer attention. My notes from the day are at the office and I've been working from home for several months so any inaccuracies in the post are mine.

BUT - choosing a yellow is easy to do, who would think twice. Grey is a good choice it looks better after being touched with dirty and oily fingers. Or was it a deliberate choice to mimic the trademark owners product.  Who can say? That's the why I suggested not focusing on other companies' products.

Paul D

Hi Paul,

I can't reply more substantially for a couple of days (tied up with work), but in brief:

None of us have ever seen any commercial gear, nor have an idea of the method of operation, beyond knowing the external interfaces (i.e. that there are four or so probes, and a connection to software).

The EPE design isn't being ripped off. Many of us here have professional org memberships, some have legal qualifications too, and we all have morals regardless. There's no interest in ripping off or incrementally tweaking someone's design - the new design is open source and being done in part for the technical challenge to get more accurate measurements in a more modern way, and make the instrument easier to use too - engineers like a challenge.

The new design is documented in paper sketches, all dated, within the comments here. You can see by comparing it to the one existing documented design, the EPE design, that it is completely different. The EPE design is a single-purpose analogue design, a bit like an analogue clock. The new design is a computer that happens to have similar external connections (probes and a computer interface). That's why it is so easy to say "sure, 40 Hz is ok" - the design doesn't care, because almost anything can be implemented in software on a computer. If 40 Hz is patented, you could choose a completely different waveform and frequency. The property of impedance cannot be patented.

The new design is actually an impedance meter. Whether commercial ones implement impedance internally I have no idea (for the reason mentioned earlier - we have no access or information on the workings of commercial designs, and don't want it either). The computer interface can expose just resistance measurements, but internally it is calculating impedance.

There was the question "why not do it simpler and use a square wave like the EPE design" and partially the answer is that yes you can if you program the internal computer to do so. It is flexible. But the intent is to use sine waves. The end computed result will be the same (it has to be, to be compatible with existing software), but done differently. The new implementation calculates impedance, then derives resistance and then throws away the impedance measurement if it is not needed. The block diagram (in paper sketches) is there, and I'm curious what parts of it could be considered ripping off any existing design.

Furthermore, by doing it differently, I'd hope it would encourage people to try new techniques. With some software modification a radar-like impedance sweep can be done. Does it have any practical purpose for archaeology? I don't know, but now the capability will exist to try it.

One more thing - there's nothing illegal (or even immoral) in making something compatible to an external interface. The EU had a directive to cover this. Commercially other manufacturers may not be happy about it, but that's not a concern for me at all. In a similar vein, any engineer who examines the EPE design will rapidly see that the new design is different - not a single component has been copied to design this new, more general-purpose measurement device. I can comment more in a couple of days if needed.

Dear Shabaz,

I never suggested that you would copy the EPE design or open up a commercial unit to have a look - why would you?

If there were an patents involved they would be by Kelvin,  Schlumberger, and the laws of nature and long since out of date.

The problem is - as you have said - is you have no experience of using this equipment in a wet field and those who have (may not have any electronics experience)  are telling you about the commercial equipment they are using - its HMI and file formats etc. These things may be covered by IP laws. It seems that the colour of the case can be(!?).

In a previous post you said that you searched for images on the internet for your diagrams - I'm sure (for brevity) you missed out the "royalty free, copyright free " part of your search in the post. Many years ago the company I worked for was pursued by a Image Library for a large payment after using copies of their images. It cost us a packet. We had used images of "Moody" oil refineries supplied by our web designers. They claimed that the images were "place holders" and we should have dealt with the paperwork, payments, or obtained the required rights ourselves.  

I suggested using QGIS in a previous post because it is open source and you could import any file format you wanted.

PS  According to the UK Government's  website "The UK has left the EU". For the past three years I have been dealing with problems caused by our withdrawal.

Phrases in this thread like "Unit X does it this way" can be very harmful to your claim of it being ALL your own work. As there are more than one person involved we are all potentially jointly and severally  for any claim made for IP infringement against any one member of this thread.

My experience with the image library suggests that there is no defence against inattention to these details.

Paul D

Hi Paul,

I shouldn't have to provide such personal information but I have a legal qualification (in the UK). Published >200 pieces of open source content, and perhaps 40 open source software projects.

If anyone has a legal problem with anything I've created or published, bring it on.

I didn't realise the full quotation was Standing on the shoulders of giants ... so that I could grind their faces in the mud.

I don't believe Richard Stallman ever said ..."Its OK to take a peek at other code before having a go" or have I missed something?

I repeat - this thread is full of references to the work of others and not original suggestions. What would Alan Turing say about having a peek inside? (Other than the Swiss made Enigma

Paul D

Referencing others is a good thing, I am not going to hide it if I have examined something - it is in the open and anyone who has a legal or moral issue can point to specifics. No-one has peeked at any code.

If Stallman read this thread (or if Turing could) I believe it is far-fetched to think they would have an issue with this design but I can't speak for them.

I repeat - this thread is full of references to the work of others and not original suggestions. What would Alan Turing say about having a peek inside? (Other than the Swiss made Enigma

 

Paul, if weren't such a mild mannered person I might get quite cross.

I've posted two completely original circuits and simulations in this thread and a completely original block diagram.

I've also participated in exchanges with others to refine my suggestions and theirs.

The most trenchant criticism of my design suggestions has been that they are too unlike what every one else does.

Of course, like any decent engineer, I have researched the subject and read some papers on it.

Other participants have made novel and helpful contributions.

The implication that the essence of this thread is rip off other peoples' work is risible.

MK

Its not the design, or the technique, which is specified by EH in the official guidelines that I have razed concerns with.

It's the "This unit does it this way" and "That unit does it that way" comments that run through this thread. What does that matter if its YOUR work?

As I have said why copy someone else's work: it may not be the best, or even good. Those who have experience in wet fields should be contributing original ideas. If you only receive instructions on how to copy others work how can YOU produce new, and exciting, equipment?

Paul D

Dear MK,

I have not said that your circuit designs are not yours or they copies of anyone's work. It never occurred to me that you would waste your time copying.

My original post was more nuanced. Why try to 'reproduce' when you have the skill to 'advance'. My concern was that you were being directed by users of existing equipment to copy/reproduce with modifications rather than being given advice and guidance on the next generation of equipment.

Paul D

Hi Shabaz, re:

shabaz  wrote:

...

There was the question "why not do it simpler and use a square wave like the EPE design" and partially the answer is that yes you can if you program the internal computer to do so. It is flexible. But the intent is to use sine waves. The end computed result will be the same (it has to be, to be compatible with existing software), but done differently. The new implementation calculates impedance, then derives resistance and then throws away the impedance measurement if it is not needed. ...

I'm sorry but I don't believe that is the case that you could get the same result. The EPE uses the same or similar technique to other working, proven instruments - it applies a DC signal, waits until a steady state is achieved, and then takes a reading. The DC is then reversed (to avoid polarisation accumulating) and the reading is repeated. Some primitive instruments may just apply the DC and wait for a fixed time before taking the measurement, that may mean taking it before a steady state is achieved, or risk polarisation, or just waste time. The 'device under test' which is being measured is not just a simple resistance. The sample is often many tens of metres long* and inevitably has some capacitance. DC is applied - either constant voltage or constant current between one set of probes, and once the injected current has settled and the resultant measuring probes return steady readings, then that is one good reading. I know, from fieldwork, that sometimes the ~3ms from 137Hz reversing frequency sometimes doesn't leave long enough for the DC conditions to settle, hence why sometimes a lower reversal rate is used to give sufficient times for the reading to settle. Sine wave excitation will not achieve this.

* processing a line of 20x20m grids, you may well be 50m away from the fixed set of probes. Even at the edge of grid nearest to the fixed pegs, when in twin-dipole mode - the most common mode - the fixed pegs must be at least 30x the distance between the two travelling probes, so 0.5m separation on frame => fixed probes can be no closer than 15m to the edge of the grid. Fixed probes then leapfrog every three or four grids.