DC voltmeter and ammeter connection circuit

When measuring the voltage and current of a certain branch, in addition to correctly selecting
the specifications, accuracy and range of the current and voltmeters according to technical requirements, the ammeter and voltmeter should also be connected to the correct position in the circuit
during wiring. Improper instrument wiring will also cause large measurement errors. For example, when measuring
the current and voltage of the branch in the figure, there are two ways to connect the voltmeter in the line
, such as point A and point B in the figure. At A, the reading of the ammeter is the current
value flowing through the wind, and the reading of the voltmeter contains not only the voltage of the island, but also the voltage value at both ends of the ammeter.
Therefore, the reading of the voltmeter is larger than the actual value. It is obvious that when R. When the internal resistance of the voltmeter is much larger than the internal resistance of the ammeter
, the voltmeter should be connected at point A; when the internal resistance of the voltmeter is much larger than the resistance of the ammeter
, the voltmeter should be connected at point B. During actual measurement, the resistance of a certain branch is often unknown
. Therefore, the position of the voltmeter during measurement can be selected experimentally. When measuring, you can try it at two points A and B respectively. If
there is little or no difference in the readings of the voltmeter between the two connection methods, it can be connected to point A; if there is little or no difference in the readings of the ammeter in the two connection methods,
it can be connected to point B; if If the readings of the ammeter and voltmeter are the same between the two connection methods , the voltmeter can be connected to point A or point B. ．