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Documents for the DMM Shield states an accuracy of +-0.1% for voltage, current, and resistance except for specific ranges highlighted. Is this accuracy obtained with factory calibration only OR does the user need to also need to calibrate the equipment? If the user needs to calibrate, can the calibration factors be stored and used by Shield OR is a external program required to make adjustment in real time. At the moment, the Shield fails to produce comparable measurement with a Fluke 88V that has lower accuracy for current and resistance readings. For the voltage readings, the accuracies are comparable but the Shields gives a poor reading based on calculated values vs measured.
I have been playing with the Digilent DMM shield and trying to understand how the shield and the ic hy3131 work. My question is about the multiplication factors which are used for converting the adc value to real value. For example, the multiplication factor in the library for 5V DC range is: 125e-1/1.8/8388608 If I'm correct, in 5V DC range the input signal is divided by 10 and fed into the adc whose reference voltage is 1.2V, so my question is why we multiply the value by 12.5? Shouldn't it be 12.0 instead because the reference voltage is 1.2V?