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| How do you measure and use a low value power resistor? |
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| soldar:
--- Quote from: technix on December 16, 2018, 03:22:41 pm --- The unknown resistor is about the 0.2 ohm range. Also I don't have low value reference resistors handy, but I do have two multimeters. --- End quote --- You can easily make low value resistors. Copper wire has a well defined resistance and can be easily found. Resistance can be easily calculated. 1000 meters of copper wire with a diameter of 1 mm will have a resistance of 22.323 Ohm. If you have nichrome wire you can easily measure the resistance of a length and then calculate what fraction you need for the resistance you want to obtain. |
| mjs:
Copper has a resistance tempco of roughly 0.4%/K at room temperature, which means that +40°C temperature rise will result i 16% change in resistance. Not very accurate. When I use a lab supply to measure small resistances, I usually just measure and set the current to 1.00 A, then connect resistor and measure voltage over it. Quite fast and no need to fiddle with two meters. |
| technix:
--- Quote from: mjs on December 25, 2018, 02:33:17 pm ---Copper has a resistance tempco of roughly 0.4%/K at room temperature, which means that +40°C temperature rise will result i 16% change in resistance. Not very accurate. When I use a lab supply to measure small resistances, I usually just measure and set the current to 1.00 A, then connect resistor and measure voltage over it. Quite fast and no need to fiddle with two meters. --- End quote --- My lab power supply don’t have the best accuracy, so an additional meter is thrown in there as a ammeter. |
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