I'm trying to get a feel for the best option for measuring resistors. I'm looking to measure from 10 ohm to 105 ohm and hoping to be at 0.5% across the range. That means I'd want to measure +/-0.05 ohm on the 10 ohm end and +/- 0.525 ohm. One issue I think should be mentioned is that the circuit for measurement will be located about 1 meter from where the resistor is attached, and will have a relay, a cord and a couple sets of terminal blocks for connection. I have been looking into various methods, but am unable to get a feel for the resulting accuracy that can be expected from different methods. A couple of points that I'd like to gather some information on if anyone can provide it.
1. Is 4 wire necessary in this case? It seems the resistance isn't that low, and most examples I've seen are for milliohm measurements. Plus, the componenents between the electronics and the actual resistor to be measured may cause some issues (or maybe not). I'd always have wires / terminals and a relay between the op amp / adc inputs and the resistor. I use 4 wire measurement for very low values on a bench meter, but never for higher ones simply because of a higher accuracy requirement.
2. I will build calibration into the system for environmental changes. Suggestions as to the method to be used would be great (PGA, digital trim pots, etc.) Known resistors can be used as a reference.
3. I'm planning on using a microchip microcontroller, and some are available with 10 and 12 bit adc. If I have one with a 12 bit, and drop the last bit, i've got a 105ohm / 2^11 = 0.0512 V. It would seem that I'm right on the edge, but maybe by ignoring the last bit, I've given myself some room. Any thoughts on this line of thinking would be great.
If you have any suggestions or ideas about the best way to go about reaching this goal, they'd be most appreciated. Thanks for your time.
1. Is 4 wire necessary in this case? It seems the resistance isn't that low, and most examples I've seen are for milliohm measurements. Plus, the componenents between the electronics and the actual resistor to be measured may cause some issues (or maybe not). I'd always have wires / terminals and a relay between the op amp / adc inputs and the resistor. I use 4 wire measurement for very low values on a bench meter, but never for higher ones simply because of a higher accuracy requirement.
2. I will build calibration into the system for environmental changes. Suggestions as to the method to be used would be great (PGA, digital trim pots, etc.) Known resistors can be used as a reference.
3. I'm planning on using a microchip microcontroller, and some are available with 10 and 12 bit adc. If I have one with a 12 bit, and drop the last bit, i've got a 105ohm / 2^11 = 0.0512 V. It would seem that I'm right on the edge, but maybe by ignoring the last bit, I've given myself some room. Any thoughts on this line of thinking would be great.
If you have any suggestions or ideas about the best way to go about reaching this goal, they'd be most appreciated. Thanks for your time.