When the megohm meter measures the end button access resistance equal to the median resistance of the instrument, the end button voltage shall not be less than 90% of the instrument rated voltage. This is the correct way to define the power supply compliance. But the capacity is determined by megger test loop cascade power resistance and resistance, in line with the sensitivity of the dc amplifier with higher megohmmeter, median size has no reaction instrument measuring the impedance of the loop resistance characteristics, has nothing to do with instrument testing capability, there is no reason to still take the size of the value of resistance for measuring instrument testing power supply in line with the ability to value reference for operators.

At present, there is no definite quantitative regulation on megohmmeter capacity in the Regulations. According to various risk data, megohmmeter capacity indicators are defined as follows:

(1) When the megohm meter measures the access resistance of the end button equal to the median resistance of the instrument, the end button voltage should not be less than 90% of the instrument's rated voltage, which is the correct definition of the power supply compliance ability. But the capacity is determined by megger test loop cascade power resistance and resistance, in line with the sensitivity of the dc amplifier with higher megohmmeter, median size has no reaction instrument measuring the impedance of the loop resistance characteristics, has nothing to do with instrument testing capability, there is no reason to still take the size of the value of resistance for measuring instrument testing power supply in line with the ability to value reference for operators.

(2) Megohm meter measures the current Id when the button short-circuit, and requires that the output voltage of the test power supply at this time is not less than 80% of the rated value. In fact, the latter indicator has no physical significance. Considering that the internal resistance of the test power supply is a compound function of the power supply and a non-constant value.

(3) The short circuit current Id of megohm meter, and the ratio of the terminal voltage and rated voltage B when the load is 20M is the indicator of the instrument capacity.

(4) The megohm meter phase user provides a test power supply compliance curve UEL= F (REL) that implies the series resistance of the instrument loop.

Obviously, the fourth method is complete, but it cannot give the capacity parameter in quantitative form. The third approach is also more reasonable. An easy to measure auxiliary index B is added. It should be pointed out that the test capability of megohm meters of different voltage levels can be evaluated not only by the size of Id, but also by the ratio B, which is basically unrelated to the voltage level, while the calculated or measured value of Id is related to the voltage level.

In "Field insulation Test implementation Guidelines" (DL474.1~6 -- 92), it is pointed out that the capacity of megohm meter is the output current value (output end measured by milliammeter). It has a certain influence on the measurement of planned index of absorption ratio. In the above measurement, megohmmeter with output current of 1Ma or above should be selected as far as possible in order to obtain more accurate measurement results.

It should be pointed out that in the results of the comparison of measuring insulation resistance, should not ignore the influence of by megger, this is because the megohmmeter capacity is different, the sample (s) are charged to the stable capacitance component values the time needed for different, and impact test point on the sample (s) in the settling time, the sample (s) to the strength of the dielectric polarization within the different, try in the insulation resistance, There will also be differences in absorptive index readings.