High-precision online dissolved oxygen measuring instrument

The invention discloses a high-precision online dissolved oxygen measuring instrument. The instrument comprises a dissolved oxygen sampling circuit, a temperature compensation sampling circuit, an MCU processor and a key display unit, wherein the dissolved oxygen sampling circuit, the temperature compensation sampling circuit and the key display unit are electrically connected with the MCU processor; the temperature compensation sampling circuit is divided into a constant current reference circuit, a differential amplification circuit and a secondary amplification circuit. According to the high-precision online dissolved oxygen measuring instrument, on one hand, in the constant-current reference circuit of the temperature compensation sampling circuit, an electric signal provided by the input end of the constant-current reference circuit is shaped through a logic inverter; after shaping, the waveform noise of the electric signal is small, and the input signal is more stable and reliable; and on the other hand