Does anybody know any application notes how to measure impedance with very low real part - around up to 1-2 Ohms. Something like long piece of metal ( pipe, pole ... )
The ADuCM350 has a very wide impedance measurement range; from milli-ohms to mega-ohms. The AN-1271 application note explains how to optimise the AFE for a particular impedance range.
I need to add to my comment above. While the ADuCM350 can measure very low impedance values, it must have at least 100Ohms in the measurement loop for stability. If the impedance that is to be measured is expected to be below this, then an additional (known) resistor should be placed in series to ensure at least 100Ohms. This resistor value can be subracted from the result. Because the measurement result is determined by a ratiometric calculation relative to RCAL, it is important that the these steps are followed:
Thank you for your answer. Where is better to place resistor – just before TIA or just after excitation output ?
Which "side" of your sensor (or unknown impedance) the resistor is placed doesn't matter. What is important though is that the sense lines (connected to P and N nodes) a connected so that they sense the total impedance, including the known impedance that you have added.
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