Field bus system and virtual field apparatus

Abstract

In a system for performing signal transmission, through a field bus, between field devices and higher-rank apparatuses connected on a transmission line, the field devices are of the analog signal type, and a substitution means is provided between the analog type field devices and the field bus so that the substitution means acts to perform communication on the field bus as a substitute for the field devices. By the substitution means, the field devices can be gradually changed to those adapted to the field bus as occasion demands, so that an existing system can be transformed step by step into a field bus system.

What is claimed is:  
     
         1 . A field bus system for performing signal transmission, through a field bus, between at least one field device and at least one higher-rank apparatus connected on a transmission line, in which said field device is of the analog signal type; and in which said system comprises a substitution means connected between said analog signal type field device and said field bus for processing an analog signal of said analog signal type field device to thereby act as a substitute for said analog signal type field device on said field bus.  
     
     
         2 . A field bus system according to    claim 1   , in which said analog signal type field device has a function for performing communication by using a digital signal superposed on an analog signal, and in which said substitution means includes means for modulating/demodulating said digital signal to thereby perform communication, and means for transmitting/receiving said analog signal.  
     
     
         3 . A field bus system according to    claim 1   , in which said analog signal type field device has a function for time-divisionally processing an analog signal and a digital signal, and in which said substitution means includes means for modulating/demodulating said digital signal to thereby perform communication, and means for transmitting/receiving said analog signal.  
     
     
         4 . A field bus system according to    claim 1   , in which said system comprises a plurality of said analog signal type field devices, and in which said substitution means has means for successively switching communication with said plurality of analog signal type field devices, means for performing signal conversion between an analog signal and a digital signal on the side of each of said analog signal type field devices, means for storing the digital signal subjected to the signal conversion, and means for controlling said storage means on said field bus.  
     
     
         5 . A field bus system according to    claim 4   , in which said storage means as a constituent member of said substitution means stores setting values related to and addresses of said respective analog signal type field devices, and in which said higher-rank apparatus acts to change said setting values and to designate said analog signal type field devices on the basis of said addresses respectively.  
     
     
         6 . A field bus system according to    claim 1   , in which said substitution means includes electric power conversion means for receiving electric power supplied from said higher-rank apparatus side and converting said electric power into its own power supply and into power supply for said respective analog signal type field devices.  
     
     
         7 . A field bus system according to    claim 6   , in which said power supply conversion means includes means for changing the electric power to be converted in accordance with the number of said analog signal type field devices substituted by said substitution means.  
     
     
         8 . A virtual field apparatus comprising: a digital signal connection terminal connected to a field bus; a plurality of analog signal connection terminals respectively connected to analog signal type field devices; means for successively selecting said analog signal connection terminals to thereby perform signal conversion between an analog signal of the selected one of said analog signal connection terminals and a digital signal; a storage means for storing the digital signal corresponding to each of said analog signal type connection terminals; and a control means for controlling signals between said storage means and said digital signal connection terminals.  
     
     
         9 . A virtual field apparatus according to    claim 8   , further comprising an electric power conversion means connected to said digital signal connection terminal and for converting electric power supplied from said digital signal connection terminal side into power supply for respective loads connected to said analog signal connection terminals and its own power supply.  
     
     
         10 . A virtual field apparatus according to    claim 8   , in which said storage means acts to store addresses for indicating apparatuses connected to said analog signal connection terminals, and in which said control means controls the reading/writing of the digital signals of the corresponding apparatuses stored in said storage means in accordance with address designation from said digital signal connection terminal.