Key Tips for Preventing Digital Multimeter Damage
When conducting electronic measurements, choosing a high-sensitivity multimeter has the following three significant advantages:
When measuring voltage with a multimeter in parallel with the circuit being tested, it will produce a shunt effect. The higher the voltage sensitivity, the higher the internal resistance (i.e. instrument input resistance) of the multimeter. The smaller the current drawn from the tested circuit, the less impact it has on the working state of the tested circuit, which can reduce the error generated when measuring high internal resistance power supply voltage. When doing electrical measurements, the internal resistance of the tested power source (such as AC power source) is very low. Therefore, the shunt effect of the multimeter can be ignored, and a low sensitivity multimeter can be selected.
The higher the voltage sensitivity, the smaller the electric power Pv consumed by the multimeter when measuring voltage. Assuming the measured voltage is U, the relationship is:
3. Easy to design high blocking. Because the voltage sensitivity is high, it means that the sensitivity of the meter head is high. A small test current can cause the pointer to deflect to full scale, achieving ohmic zeroing of the resistance range. Even in high impedance, lower battery voltage can be used.
The error in measuring voltage with a multimeter can be analyzed using the following diagram. Assuming the measured voltage is U and its internal resistance (or equivalent internal resistance) is r. (b) The dashed box on the right side of the figure is the equivalent circuit of the voltage range, with an internal resistance of RV and 0 indicating an indicator of zero internal resistance (the same below). Connect a multimeter in parallel to the circuit under test, and set the reading of the multimeter to U. The relationship is:
(a) Equivalent circuit of the measured voltage source; (b) The relative measurement error of the equivalent circuit when measuring voltage is:
If rv<0 in the equation, it indicates that U1<U, that is, the measured value is lower than the actual voltage value. As the ratio RV/r increases, the absolute value of relative error | rv | will decrease. The relative error curves shown in the following figure provide the rV values for three cases: Rv/r=l, 10, and 100. As shown in the figure, when the internal resistance of the measured power supply voltage is low and satisfies the condition of Rv>100r, | rv |<1%, and the measurement error can be ignored. However, when the internal resistance of the tested circuit is high and comparable to Rv, significant measurement errors will occur.
