An air conditioner current loop communication circuit includes an indoor unit current loop communication circuit and an outdoor unit current loop communication circuit connected to each other via a communication connection wire and an AC power connection wire to form a current loop communication loop, an indoor microcontroller unit (MCU) and an outdoor MCU configured to communicate with each other through the current loop communication loop, and a switching power supply circuit connected in series to the communication connection wire or the AC power connection wire and configured to output a DC power to the current loop communication loop.

An industrial process field device includes an active component, a switch, a switch monitor, and a controller. The active component may be a sensor configured to sense a process parameter, or a control device configured to control a process of the industrial process. The switch is electrically coupled to first and second terminals and is configured to electrically connect the first and second terminals when in a closed state, and electrically disconnect the first and second terminals when in an open state. The switch monitor is configured to detect a current state of the switch corresponding to the closed or open state, and generate a state output indicating the current state. The controller is configured to set the switch in the open or closed state, and generate a notification based on the state output that indicates at least one of the current state of the switch and a condition of the switch.

An air conditioner current loop communication circuit includes an indoor unit current loop communication circuit and an outdoor unit current loop communication circuit connected to each other via a communication connection wire and an AC power connection wire to form a current loop communication loop, an indoor microcontroller unit (MCU) and an outdoor MCU configured to communicate with each other through the current loop communication loop, and a switching power supply circuit connected in series to the communication connection wire or the AC power connection wire and configured to output a DC power to the current loop communication loop.

A component in a process control device such as a valve actuator, for example, is coupled to a protective circuit. In particular, the protective circuit allows an analog current loop (e.g., 4-20 mA) to provide to the component a secondary operating voltage, derived from the analog current loop, in the absence of a primary operating voltage source (e.g., during a power failure), such that the component is not damaged when a signal from the analog current loop is applied to the process control device in the absence of the primary operating voltage source.

An industrial process field device includes an active component, a switch, a switch monitor, and a controller. The active component may be a sensor configured to sense a process parameter, or a control device configured to control a process of the industrial process. The switch is electrically coupled to first and second terminals and is configured to electrically connect the first and second terminals when in a closed state, and electrically disconnect the first and second terminals when in an open state. The switch monitor is configured to detect a current state of the switch corresponding to the closed or open state, and generate a state output indicating the current state. The controller is configured to set the switch in the open or closed state, and generate a notification based on the state output that indicates at least one of the current state of the switch and a condition of the switch.

Control electronics for a two-wire process device, which two-wire process device can be connected to a two-wire loop. The control electronics comprises an input circuit and a control unit connected to the input circuit, wherein the input circuit is used in a first operating mode to set a current and/or voltage in the two-wire loop by means of a control signal transmitted by the control unit. The input circuit is used in a second operating mode to automatically, in particular independently of the control unit or independently of the control signal transmitted by the control unit, to set the current and/or the electric voltage in the two-wire loop.