By hvhipot 
The technical principle of the insulation resistance tester:
According to Ohm’s law, the measured resistance Rx is equal to the applied voltage V divided by the current I through it. The working principle of the traditional high resistance meter is that the measurement voltage V is fixed, and the resistance value is obtained by measuring the current I flowing through the sampling resistor.
It can be seen from Ohm’s law that since the current I is inversely proportional to the resistance, not proportional, the display value of the resistance is non-linear, that is, when the resistance is infinite, the current is zero, that is, the zero position of the meter is ∞, its The nearby ticks are very dense and the resolution is low. The entire scale is non-linear. Also, when measuring different resistances, the voltage V will also change somewhat, so the ordinary high resistance meter has poor accuracy and low resolution. It is to measure the voltage V across the resistor and the current I flowing through the resistor at the same time, complete the calculation of the voltage divided by the current through the internal large-scale integrated circuit, and then display the resistance value in digital after A/D conversion. , even if the voltage V at both ends of the resistor and the current I flowing through the resistor change at the same time, the displayed resistance value does not change due to the change of the measured voltage V or the change of the current I like the ordinary high resistance meter. Changes in voltage, measured resistance, power supply voltage, etc. have little effect on its results, and its measurement accuracy is very high (). Several.