Patent ID: 9684322
Date: 2017-06-20
CPC Classifications: G05F,H02H

Claim:
1. A voltage limiting device to limit DC voltage transmitted from a trunk circuit to a spur circuit of a distributed control network in which the trunk circuit cooperates with the spur circuit in transmitting AC voltage data signals superimposed on the DC voltage between a field device attached to the spur circuit and a control processor attached to the trunk circuit, the voltage limiting device comprising: an input terminal for receiving an input voltage from the trunk circuit; an output terminal for supplying an output voltage to the spur circuit; a voltage regulation device connecting the input terminal with the output terminal, the voltage regulation device being configured to deliver an output voltage to the output terminal based upon the input voltage from the trunk circuit, the voltage regulation device being operable in a first mode wherein the output voltage is equal to the input voltage, the voltage regulation device being operable in a second mode wherein the output voltage is equal to a threshold voltage; a control device connected to the output terminal and to the voltage regulation device, the control device being configured to place the voltage regulation device in the first operating mode when the voltage at the output terminal is below the threshold voltage, the control device being configured to place the voltage regulation device in the second operating mode when the voltage at the output terminal exceeds the threshold value or would exceed the threshold value if the voltage regulation device were operating in the first mode; and an AC signal device connected to the input and output terminals in parallel with the voltage regulation device, the AC signal device configured to carry the AC data signals between the input and output terminals while the voltage regulation device is operating in the second mode.