AUTOMATIC CORRECTION METHOD FOR ZERO-POINT/SPAN SHIFT OF MASS FLOW CONTROLLER AND MASS FLOW CONTROLLER CONTAINING AUTOMATIC CORRECTION FUNCTION

摘要

PURPOSE: To ensure the flow rate control for a long period of time and with high accuracy by securing the coincidence of temperature distributions between the working and correction states of the sensor part of a mass flow controller(MFS) and then correcting occasionally and automatically the zero-point shift and the span shift with the MFC kept on a production line. ;CONSTITUTION: A current converter part 20 is provided to change in steps the level of the current supplied to a sensor coil 12. Then each unbalanced voltage caused based on the current change of the part 20 is stored in an initial unbalanced voltage storage part 23 via an unbalanced voltage reading part 21 in an initial correction state of a sensor. Meanwhile each unbalanced voltage detected in a sensor working state under the same conditions as the initial correction state is stored in a detected unbalanced voltage storage part 22. Both zero-point and span shift correction values are obtained through the comparison and calculation of both unbalanced voltage levels. Based on these correction values, both the zero-point and span shifts are corrected by a zero-point correction part 25 and a span correction part 26 respectively. In such a constitution, the highly accurate flow rate control is assured for a long period of time.;COPYRIGHT: (C)1993,JPO&Japio