Development Of Hardware For Digital Coriolis Mass Flow Transmitter

The Coriolis mass flow meter is developed based on theory of Coriolis force. It is with ability of measuring mass flow directly as well as volume flow, density, temperature with high accuracy. It can be applied to a variety of fluid. Traditional Coriolis mass flow meter adopts analog drive mode and signal processing technology based on analog circuitry. It is sensitive to noises and performs poorly in tiny flow, resulting narrow measurable range. The flow tubes may stop vibrating during two-phase flow or batch flow, resulting failure in measurement. To conquer these disadvantages, a digital Coriolis mass flow transmitter is developed based on DSP.The Coriolis mass flow transmitter is mainly composed of a signal pickup module, a driving module, a temperature compensation module, and a power fail protection module. In the signal pickup module, two high performance ADCs are adopted to pick signals from two sensors at the same time. The trouble of phase drift is solved by carefully selecting the cutoff frequency and capacitors. Analog drive mode, semi-digital drive mode based on MDAC, and pure-digital drive mode based on wave synthesis are all used to vibrate flow tubes. A three wire temperature compensation circuitry with lead length compensation is used to eliminate influence of lead resistance in temperature measurement. In the power fail protection module, ferroelectric nonvolatile RAM with read/write time of nanoseconds is used to save important data when the power fails. A felicitous voltage is supervised, so the power fail protection module can response earlier to win more time for data saving.