Field device
To provide reliable notification of a fault state when a power supply to a calculation processing portion is in the OFF state when a power supply to a communication processing portion is in the ON state. An isolating circuit, an inverting circuit inverting a signal branch-outputted through an output line of the isolating circuit, and a selecting circuit that uses the signal outputted from the output line of the isolating circuit as a first input and the inverted signal from the inverting circuit as a second input, to select either the first input or the second input, depending on a selection setting status thereof, to output the selected signal to the communication processing portion are provided. A +5 V voltage is applied through a resistor to the output line of the isolating circuit. This +5 V voltage is produced through the power supply supplied from the second double-wire transmission path.
1. A field device comprising:
a calculation processing portion that operates by receiving a power supply that is sent through a first transmission path;
a communication processing portion that operates by receiving a power supply that is sent through a second transmission path;
an isolating circuit that is provided between the calculation processing portion and the communication processing portion, wherein a burnout signal that is produced by the calculation processing portion is outputted to the second transmission path by the communication processing portion through the isolating circuit;
an inverting circuit that inverts a signal that is branch-inputted through an output line from the isolating circuit;
a selecting circuit that receives a signal from the output line of the isolating circuit as a first input and the inverted signal from the inverting circuit as a second input, and that selects either the first input or the second input in accordance with a selection setting status, to output, to the communication processing portion, the selected signal; and
a selection setting status transmitter that transmits the selection setting status in the selecting circuit to the calculation processing portion, wherein:
the isolating circuit maintains a voltage level of the output line at a predetermined voltage level that indicates a predefined burnout signal when the power supply to the calculation processing portion is turned OFF when the power supply to the communication processing portion is tuned ON; and
the calculation processing portion further comprises:
a rectifier that rectifies, based on the selection setting status transmitted to the calculation processing portion by the selection setting status transmitter, the burnout signal produced by the calculation processing portion to the burnout signal which the selecting circuit outputs to the communication processing portion when the power supply to the calculation processing portion is turned OFF, when the power supply to the communication processing portion is turned ON, and when the burnout signal produced by the calculation processing portion is different from the burnout signal which the selecting circuit outputs to the communication processing portion.