Appendix J

 Advantages of Super and ULTRA MiniRes over the Standard MiniRes

The high-power Super MiniRes (serial number between 100 and 140) uses several methods to improve the SNR compared to the original Standard MiniRes (serial numbers less than 32). Here is a list of those improvements:

1) The Super MiniRes has a maximum transmitter current output amplitude of 10.0 milliAmps and can easily be modified to 20.0 milliAmps. The ULTRA is standard with 20.0 milliAmps. Whereas the original MiniRes has a maximum of 5.0 milliAmps - giving a factor of 2 or 4 improvement in signal-to-noise-ratio (SNR).

2) The Standard MiniRes has a very simple (but extremely accurate) square wave transmitter waveform with some DC offset.  The Super and ULTRA  MiniRes use a different and very specific type of transmitter waveform that, by itself, provides a SNR improvement of a factor of about 3.6 compared to the conventional unit.  But the improvement in random noise SNR is not the only thing the special waveform does. It also, inherently, provides extremely deep "notches" in the response at 50 and 60 Hertz. 

3) Lastly, the Super and ULTRA MiniRes have a narrower (sharper) bandpass filter to reject any noise outside of its 5.00 Hertz band compared to the Standard MiniRes.  Not only is the width of that filter narrower, but the "skirts" of the filter have a greater rejection slope.  This narrower and higher-sloped-skirt filter improves the SNR by about a factor of 1.3 to 1.4 compared to the Standard MiniRes. 

The total improvement in SNR is given by the product of all of those individual SNR improvements: 

2 X 3.6 X 1.35 = 9.72 improvement in SNR of the Super unit over the Standard MiniRes

and twice that (19.44) for the Super units modified to 20 milliAmps and all the ULTRA MiniRes.

                                     

There is also an improvement due to the strong rejection of the 50 and 60 (and 10, 20, 30, 40, etc) Hertz noises.  But, that is hard to calculate since it is dependent on the particular noise level of the area where one is working.  Clearly, the Super MiniRes has about a ten fold greater SNR than the Standard MiniRes.  The ULTRA has about a twenty fold greater SNR

There are other major improvements in the Super MiniRes compared to the Standard MiniRes:

a) the Super MiniRes frequency is 5.00 Hertz compared to 30.00 Hertz for the Standard MiniRes. So, there is much less need to worry about skin effects when using very long arrays in very conductive environments. There is a 2.5 Hertz option for the ULTRA so that Wenner arrays with  “a” spacings of up to 300 meters can be used before skin effects become noticeable.

b) The Super MiniRes has a new high voltage automatic DOUBLER.  This allows many more readings without exhausting the batteries.  The DOUBLER only comes on when needed - thus saving batteries.  The DOUBLER operation is completely transparent to the user. It switches on automatically in a fraction of a millisecond and remains ON until the unit powers down.  The ULTRA uses the same technology

c) The Super and ULTRA MiniRes are nearly all surface mount technology on the printed circuit board (PCB).  This reduces assembly costs, makes the meter lighter weight, and more rugged to vibration and abuse. The ULTRA has its PCB mounted on four rubber shock absorbers.            

 

d) The Super and ULTRA MiniRes have special "cut-outs" on the PCB which help to minimize leakage currents on the PCB.  Thus, humidity has less of an effect on the leakage current between the transmitter and receiver sections of the Super and ULTRA MiniRes. Much effort was spent on the Standard MiniRes to minimize PCB leakage currents - but it does not have the special "cut-outs" which are so effective.  All resistivity meters suffer to some degree from this problem.

e) Because of these (and a few other) improvements, the Super MiniRes has ten times more resolution in the resistivity mode: 1 milliohm for the Super MiniRes versus 10 milliohms for the Standard MiniRes.  The IP mode in the Super MiniRes has one hundred times more resolution than the conventional unit! The IP mode was "pushed" so that the last significant digit may appear a bit noisy and may drift over a day or so - but that increased resolution may allow laboratory measurements to be made with the unit. That IP resolution is better than one thousandth of one degree in phase! The ULTRA has an additional tenfold increase in resolution and a three position range switch.

The Super MiniRes is a major improvement over the Standard MiniRes - not simply an increase in transmitter power. However, the Standard MiniRes is more than adequate for electrical grounding surveys, archeological surveys, lab measurements, and shallow to moderate depth geotechnical and groundwater surveys. The Super MiniRes has been tested side by side with the Sting and Terrameter to “a” spacings of 200 meters (600 feet) and 600 meters (1800 feet) between current electrodes at resistive field sites. With the 2.5 Hertz option on the ULTRA, the “a” spacing can go 300 meters  (1000 feet).



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