The Relation of Multimeter Ammeter Internal Resistance to Electric Power
Relationship Between Multimeter Current Internal Resistance and Electric Power
Under ideal conditions, the internal resistance of the multimeter's current range should be zero. Due to the existence of internal resistance, a certain voltage drop will inevitably occur when measuring current with a multimeter, resulting in measurement errors.
The lower the internal resistance of the current range, the less electric power the multimeter consumes during measurement.
With the same current range, the lower the multimeter internal resistance, the lower its full-scale voltage drop and the smaller the error in current measurement. For the same multimeter, the full-scale voltage drop values of each current range may differ.
For the same multimeter, the larger the current measuring range, the smaller the internal resistance and the smaller the measurement error.
Therefore, to reduce errors in current measurement, a higher current range may sometimes be selected. However, the range should not be set excessively high, otherwise the reading error will increase significantly when measuring small currents.
When the internal resistance of the current range is approximately 1% of the total resistance of the measured circuit, the influence of the multimeter voltage drop on the measurement can be ignored.
II. What is the Typical Internal Resistance of Multimeter Current Ranges?
Microampere ranges adopt high-sensitivity meter movements, whose internal resistance is high, ranging from several ohms to tens of ohms, or even hundreds of ohms.
The internal resistance of milliampere ranges is much lower, within tens of ohms. Ampere ranges have extremely low internal resistance, mostly composed of parallel short-type shunt resistors, with internal resistance less than 1 ohm.
The internal resistance varies greatly among different ranges.
Connecting resistors in parallel with a microampere meter can expand its measuring range. It can be seen that for the same meter movement, the larger the expanded range, the smaller the equivalent internal resistance.
The full-scale current of the meter movement can be used to calculate the shunt resistance according to the required measuring range. The resistance value obtained after the shunt resistor is connected in parallel with the internal resistance of the meter movement is the result you need.Formula: R total = (R × XR) ÷ (R + XR)
Approximate resistance values can also be obtained by direct measurement with a high-precision digital multimeter.
