Abstract: A portable periodic signal processor consists of 8098 chip　microprocessors and DMF5002 lattice liquid crystal plane display． It can　display the waveform, frequency　spectrum and data of the signal simultaneously． The amplifying of figure, and its reducing and moving are controled by keyboard． The screen can be copied. The processor can be applied to diagnose machine failures. This paper introduced the method for lattice liquid crystal screen display, the applying of numeral wave filtration， the error analyzing， the strategy of reducing error，as well as some applicatiom examples.