This instrument is controlled by an intelligent microcontroller chip, with high precision, high reliability and high stability; AUTO RAMP function enables simultaneously testing action time and action current of fault; according to LCD icon prompts, there is an instruction to check whether the wiring is correct; after test is completed, the measurement results are automatically displayed; there are 0 ° and 180 ° phase options, which can detect quickest trigger time; “OL” is displayed for over range; the instrument is equipped with FUSE safety protection and CAT III 300V safety level.