Coriolis Mass Flow Meter Transmitter Circuit And Its Circuit Realization

Coriolis quality flow meter (CMF) which categorized in direct-style quality flow meter utilizes Coriolis principle to realize its high degree of accuracy and low degree of mechanical loss. Transmitter is one of the most important components of CMF.After pantological research on CMF theory system, physical meaning of Coriolis force and its application in quality flow meter are elaborated, and then structure and working course are analyzed. Furthermore, principle for design is raised as a guideline of following work.A mechanism to realize the principle is designed and detailed illustration on the circuit which validity and effectiveness are tested both by simulation and experiment is given.Analog circuit mainly realizes the drive system consisting of physical loop and gain-controlled loop and signal pre-processing system which acts on output signals from primary instrument. The drive system outputs to drive magnetic loop on the primary instrument, accordingly simulate the work condition of Coriolis force. The difficulty lies on keeping the amplitude in a proper range to activate the primary instrument, neither too high nor too low. The signal pre-processing system acts on primary phase signal and temperature signal to make it available for digital circuit.There are three branch circuits for phase signal. Two branches are completely similar to process phase signals respectively from right and left sensors on primary instrument. The third branch processes phase signal to make it precede the arrival of the other two ones. The function is to warn MCU of the arrival of right and left phase signals. The signal pre-processing system also has circuit to extract temperature signal via platinum thermistance, in which three-wire system and constant current measurement method are adopted.Before the design of digital circuit, measurement method of phase difference is discussed. Two-way zero passage phase detector is chosen as solution finally. Based on the principle of this, digital circuit is designed to contain zero passage phase detector module, counter module and MCU module. The zero passage phase detector extract zero passage information from the two phase inputs respectively. The counter module is designed to measure the length between zero passages and the counted result may be invoked by MCU. The MCU module mainly contains MCU chip and its power supply circuit and quartz oscillator. Its function is to coordinate the works of modules and figure out the quality information finally.