The JSY-MK-109 single mutual inductance electric energy quality testing instrument is a highly integrated measurement, digital communication, etc., which can complete electric energy measurement, collection and transmission, single-phase AC parameter measurement application product, accurately measure single-phase AC voltage, current, power, electric energy and total electric energy and other electrical parameters, and has 1 9V power output, 1 RS-485 communication interface, MODBUS-RTU protocol, with excellent cost performance.