This is a smart piece of analog circuitry and is based on unsophisticated and cheap components. Thus, it could possibly be used for lab experimentations in magnetic field measurements but I already see a few potential (real!) problems in it if it would be used for any practical use:
1. Polarization switching through relay will shortly give operational problems due to the fast wearing of its contacts.
2. Frequency measurement by period counting is very prone to imprecision due to spikes in the amplified signal.
3. Even in the high resolution mode of 0.1Hz, this can only give a precision of 2.5nT in the best case.
4. The pre-set measurement period of 8 seconds is incompatible with a walking operator
5. The lack of measurement recording or even of any potential connectio to an external data logger makes this system unusable for surveys.
It would be easy to cure the problem 1 by replacing the relay by a few HEXFET's making the switching perfectly static.
The problem 2 is MUCH more difficult to solve without any data processor. You just need to cross your fingers and hope that the environmental noise does not generate any spikes. A single signal period missed or added generates an error of 23nT!!!
With such a circuit, I do not think it would be possible to get a precision down to 1nT, thus, the problem 3 is not really solvable on this base.
The problem 4 is not really a problem provided the right type of proton-rich fluid is being used allowing a much shorter polarization period to be used.
The problem 5 needs to be solved by the use of a digital processor in order to at least provide a serial link to an external data logger.
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« Last Edit: July 09, 2009, 11:39:01 am by willy bayot »