Patent ID: 10033434

Abstract:
A loop powered process instrument comprises a control system including a control circuit, a modem circuit and a loop output circuit. The control circuit measures a process variable and develops a measurement signal representing the process variable and includes a loop control circuit and a communication circuit. The modem circuit is operatively connected to the communication circuit and includes a modulation input port and a modulation output port. The loop output circuit receives a measurement signal from the loop control circuit and is connected to the modulation input port. A two-wire circuit is for connection to a remote power source using a two-wire process loop. A power supply with isolation is connected to the two-wire circuit and the loop output circuit to isolate the two-wire circuit from the control system. The power supply receives power from the two-wire process loop and supplies power to the control system and draws loop current on the two-wire process loop in accordance with the measurement signal and provides the modulation output on the loop current. A bypass circuit with isolation is connected between the two-wire circuit and the modem circuit modulation input port for providing input modulated signals to the modem circuit bypassing the power supply.