Resistivity tester is a kind of on-line panel instrument, which can monitor resistivity and temperature at the same time, and has low limit alarm function. It is widely used in pharmaceutical, electronic, chemical and other industries for on-line monitoring of industrial process water quality. It adopts the technology of single-chip microcomputer, which can set the low limit alarm points of temperature coefficient, electrode constant and resistivity of pure water freely through the buttons on the panel. It is an ideal instrument for all kinds of small and medium-sized pure water equipment.