General and laden cent is 3 kinds big, reach resistor sex load (like bulb) , capacitance sex is laden (if exchange type power source,supply implement) reach inductance sex load (if transmission is motor) . To sine wave character, these 3 kinds of load all can be used. Wave of square wave, a flight of stairs can be used at resistor sex and capacitance sex load only, because sensibility turns over the deadly injury that electromotive force is wave of a flight of stairs ladenly, and capacitance sex load needs taller peak value voltage to come drive, the product of wave of square wave, a flight of stairs has the character of high peak value fitly, but have harmonic component because of wave of a flight of stairs, to certain instrument character can be disturbed because of harmonic and generation reads value mistake or misoperation.