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.

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

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

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