| 摘要 |
PURPOSE:To enhance the function of filter in the optimum state at all times by providing a signal history storage means digitizing and storing the history of an analog signal and using a mean value of the signal stored over a prescribed number of periods by the storage means and providing a filter coefficient acquisition means obtaining the digital filter coefficient by said means value. CONSTITUTION:A CPU 11 applies normalizing processing while fetching sequentially a process conversion detection value for each prescribed period and a raw data area 16b of a RAM 116 stores the present raw data PV'. Then the CPU 11 reads the sample number being the process variable detection value from the counter 16c of the RAM 16 so as to discriminate whether or not the sample number reaches the sample number of the period J. When the sample number reaches J number of times, the data from the PVn-j of J preceding periods till the immediately preceding period Vn-1 are read and the mean value is obtained. In obtaining the filter coefficient DF by using the mean value, the filter coefficient DF is used to obtain the present process variable input PVn. Thus, the optimum filter coefficient is decided at all times in response to the change in the analog signal and the filter coefficient is used to obtain the analog signal input, then the effect of noise is not caused. |
