What should I do if the voltage signal of the digital multimeter is weak during use?
Measuring weak voltage signals requires attention to error sources such as thermoelectric potential, common-mode interference, and electromagnetic induction. These errors are generally on the order of 10 μV, which will seriously interfere with small-signal measurements. Using the same material, twisted pair or shielded test cable can reduce the error of thermal EMF and electromagnetic induction. Before measuring Ue, you can first judge the size of the total error introduced by these error sources, use the "relative" operation of the multimeter to eliminate the interference of fixed errors, and then measure Ue to get more accurate results.
First connect the two test leads of the multimeter to terminal C in Figure 1 at the same time. At this time, the reading of the multimeter is caused by the error source of thermoelectric potential, common mode interference, and electromagnetic induction, and observe its changes. If the reading fluctuates within a small range, it is considered a fixed error. Press the "relative" menu key of the multimeter, the multimeter will record the current reading value, and subtract the reading value from each subsequent measurement result before displaying, so that the interference of fixed errors can be eliminated. Then measure the voltage difference between terminal C and the "-" terminal of Ui, and the reading is the Ue value after excluding the interference of fixed errors, which can accurately reflect the real Ue size.
