The relationship between the internal resistance of multimeter current and electrical power
1、 The relationship between the internal resistance of multimeter current and electrical power
Ideally, the internal resistance of the multimeter's current range should be equal to zero. Due to the presence of internal resistance, there will inevitably be a certain voltage drop when using a multimeter to measure current, resulting in measurement errors.
The smaller the internal resistance of the current range, the lower the electrical power consumed by the multimeter when measuring current.
1) When the current range is the same, the smaller the internal resistance of the multimeter, the lower the full scale voltage drop, and the smaller the error in measuring current. For the same multimeter, the full scale voltage drop values for each current range can be different.
2) For the same multimeter, the larger the current range, the smaller the internal resistance, and the smaller the measurement error.
Therefore, in order to reduce the error in measuring current, it is sometimes preferable to choose a higher current range. Of course, the range should not be too high to avoid a significant increase in reading error when measuring small currents.
3) When the internal resistance of the current range is about 1% of the total resistance of the circuit being tested, it is not necessary to consider the impact of the multimeter voltage drop on the measurement.
2、 What is the internal resistance of the current range of a multimeter?
In terms of microampere range, a high sensitivity meter head is required, and the internal resistance of the meter is very high, ranging from a few ohms to tens of ohms, or even hundreds of ohms.
The internal resistance in the milliampere range is much lower, within a few tens of ohms. In the ampere range, the internal resistance is extremely low, mostly connected in parallel by short-circuit diverters, and the internal resistance is within 1 ohm.
There is a significant difference in internal resistance between different gears.
The parallel connection of resistors in a microampere meter can expand the range, indicating that for the same meter head, the larger the extended range, the smaller the equivalent internal resistance it presents.
The shunt resistance can be calculated based on the full bias current of the meter head and the required current range. The resistance value after parallel connection between the shunt resistor and the internal resistance of the meter head is the answer you need. R total=(R score XR table) ÷ (R score+R table)
An approximate resistance value can also be obtained by directly measuring with a high-level digital meter.
