Jak can a multimetr measure high resistance?
The maximum range of resistance range for 31/2 bit and 41/2 bit digital multimeter is general 20M Ω.
For a 31/2 digit digital multimeter, using different resistance range can only measure resistance within the range of 0.1 Ω to 19.99M Ω; For a 41/2 digit digital multimeter, it can only measure resistance within the range of {8}}.01 Ω to 19.999M Ω. When the measured resistance Rx Greater than or equal to 20M Ω, the instrument will Display The Overflow symbol "1".
Experiments have shown that using the following "parallel resistance method" can expand the range of a 31/2 bit or 41/2 bit digital multimeter from 20M Ω resistance to 100M Ω.
1, Pomiar metoda
Prepare a resistance R1 of over ten megaohms in advance, set the digital multimeter to the 20M Ω range, measure the resistance value R1, and then connect the measured resistance Rx in parallel at both ends of R1, and then measure the total parallel resistance R.
It is easy to derive the calculation formula based on the parallel connection of resistors.
2, Pomiar przykłady
The measured resistance is an unidentified high resistance resistor Rx, and R1 is selected with with a nominal resistance value of 10M Ω. Using the 20M Ω resistance range of a digital multimeter, the measured resistance value of R1 is 10.05M Ω.
After connecting Rx and R1 in parallel, measure the total resistance value R=7.70M Ω. Substituting into equations (4-13) yields
Based on this, the nominal value of the measured resistance should be 33M Ω.
3, pomiar środki ostrożności
1. When the rezystancja wartość of the zmierzony rezystor Rx przekracza 100M Ω, the total resistance value R after parallel connection is very close to the rezystancja wartość of wybrany standard rezystor R1. In add, the digital multimeter itself has an error of ± 1 word, which will increase the measurement error.
Therefore, this method is not suitable for measuring resistance values greater than 100M Ω.
2. Podczas pomiaru operacji, zmierzony rezystancja Rx powinien być bezpieczny podłączony w równoległy z standardowy rezystancyjny R1, i jeśli konieczny, the two can be fixed with a krokodyl zacisk.
