A few clarifications in the testing of digital multimeters
Ø Regarding the high resistance, it is normal that the test effect of resistance is different from the test effect of pointer meter. This is firstly due to the slight difference in the test premise.
Ø When testing the physical quantity related to polarity, its polarity display is corresponding to the meter pen. That is to say, when the polarity is not shown, the red pen touch point is the potential or current inflow end, and when the polarity is shown as "-", the red pen touch point is the low end of the potential or current outflow end.
Ø Resistance and diode block are different from pointer meter. When measuring the resistance of pointer meter, the red and black pens are opposite to the polarity of the test source, i.e. the black pen is the positive end of the test source and the red pen is the negative end. While the digital table with the test source polarity differences, that is, the red pen for the test source positive end, black pen for the negative end, which reveals the voltage and current blocking divergence. This will not be mixed up, which is better than the pointer meter.
Ø With regard to the triode which does not know the polarity or the order of the pins, it can be detected by the triode hfe block for several times by changing the pin to distinguish and determine the electrodes of the triode.
Ø Calibration.
The accuracy of digital multimeter
Accuracy refers to the large allowable error under a specific use environment. In other words, accuracy is used to indicate how close the measured value of a digital multimeter is to the actual value of the signal being measured.
For digital multi-meters, accuracy is usually expressed as a percentage of the reading. For example, a 1% reading accuracy means that when the digital multi-meter display is 100.0V, the actual voltage may be between 99.0V and 101.0V.
There may be specific values added to the basic accuracy in the detailed instructions. It means the number of words to be added for the transformation of the *right end of the display. In the previous example, the accuracy may be labelled as ± (1% + 2). So if the GMM reads 100.0V, the actual voltage will be between 98.8V and 101.2V.
The accuracy of an analogue meter is based on the error at full scale, not on the displayed reading. Typical accuracy of an analogue meter is ±2% or ±3% of full scale. Typical basic accuracies for digital multi-meters are between ±(0.7%+1) and ±(0.1%+1) of the reading, or better.
