Please tell me about the internal resistance of analog testers.

QThe specifications of the HiTester 3030-10 and Multi Tester 3008 indicate an internal resistance of 20 kΩ/V. Please tell me about the effects of the tester’s internal resistance.


Although internal resistance would ideally be infinite, testers always have a certain internal resistance. DMMs have a high internal resistance that is generally at least 10 MΩ (although it may vary with the measurement range), while analog testers (3030-10, 3008) have a DC voltmeter with an internal resistance of 20 kΩ/V (the 3030-10’s 0.3 V range has an internal resistance of 16.7 kΩ/V). When measuring a circuit’s voltage, the tester’s internal resistance is connected in parallel with the actual measurement circuit. The magnitude of the effect of the internal resistance is determined by the proportion of the resistance of the circuit being measured to the tester’s internal resistance, and it decreases as the tester’s internal resistance increases. Consequently, it is necessary to exercise caution when measuring a high-resistance circuit such as a transistor base circuit with a tester that has a low internal resistance, because the indicated voltage will be lower than the actual voltage.