Intrinsically safe barrier and field bus system

摘要

PROBLEM TO BE SOLVED: To extend a communication enable transmission range and condition of the number of connected field devices by connecting an impedance correction circuit decreasing an impedance at a data transmission frequency band in parallel with a load resistor in a barrier. ;SOLUTION: A resistor 61 and a Zener diode 62 in a barrier 6 are used to limit a current and a line voltage of a transmission line 5 thereby suppressing an energy applicable to a dangerous area. A communication signal is remarkably attenuated by an internal resistance of the barrier 6 in combination of the resistance of the resistor 61 and the resistance of a fuze 63 to limit the length of the transmission line 5 and the number of field devices to be connected. In order to reduce the entire impedance of the barrier, an impedance correction circuit 64 at a frequency band of data transmission (using Manchester cord at 31.25kbps) is connected in parallel with the resistor 61. Thus, the available transmission range is extended and the number of connected field devices is increased.;COPYRIGHT: (C)1997,JPO