| ??? 07/08/09 19:50 Modified: 07/08/09 19:53 Read: times |
#166883 - Assuming and supposing... Responding to: ???'s previous message |
Saman said:
current is supposed to be constant during measurement. Current scheme is just like a DMM. a current measuring resistor produces a voltage drop that is buffered and read by ADC. The current can change depending on the actual load! When you change the range of DMM then you often change the shunt, where the current causes the voltage drop to be measured. But changing the shunt can make change the current, which is erroneously assumed to be constant. This happens quite often Saman said:
but if I can solve auto calibration problem maybe I can solve drift problem, because I can auto calibrate at power on and then temperature remains constant during measurement and also I can solve long term drift. Every calibration needs a reference, which must stay constant. If the reference shows drift by itself, then it's no good reference. Whether "auto calibration" will work depends a lot on your application. There are very nice calibration schemes to compensate for supply voltage changes (by using ratio metric measurement, e.g.), offset voltages, gain errors and so on. But we need more details from you to analyse what's helping. Kai |
