Abstract: A diagnostic field device for coupling to a two-wire process control loop of an industrial process control or monitoring system includes digital communication monitoring circuitry which is configured to couple to a two-wire process control loop. The digital communication monitoring circuitry is configured to receive a digital communication signal from the two-wire process control loop. Timing circuitry in the diagnostic field device provides a timing output. Diagnostic circuitry provides a diagnostic output based upon the digital communication signal and the timing output.

Abstract: A diagnostic field device for coupling to a two-wire process control loop of an industrial process control or monitoring system includes digital communication monitoring circuitry which is configured to couple to a two-wire process control loop. The digital communication monitoring circuitry is configured to receive a digital communication signal from the two-wire process control loop. Timing circuitry in the diagnostic field device provides a timing output. Diagnostic circuitry provides a diagnostic output based upon the digital communication signal and the timing output.

Abstract: A diagnostic device for coupling to a process control loop includes digital communication circuitry configured to receive a digital communication signal from the process control loop. The digital communication signal is a digitally modulated analog signal on the process control loop which is modulated to a plurality of discrete analog signal levels representative of digital values. Diagnostic circuitry diagnoses operation of the process control loop which may include field devices of the process control loop based upon the digitally modulated analog signal.

Abstract: A process device is configured for coupling to a two wire process control loop. Loop current output circuitry is configured to apply an output current to the two wire process control loop. Loop current verification circuitry is coupled to the two wire process control loop and configured to detect errors in the applied output current. At least a portion of the loop current verification circuitry is independent from the loop current output circuitry.

Abstract: A process field device for coupling to a two wire process control loop includes a field device circuitry and a switching regulator to power the circuitry. A series regulator provides a regulated supply voltage to the switching regulator. A noise filter reduces the amount of noise from the switching regulator which enters the two wire process control loop.

Abstract: A process device for use on an industrial process control system includes a quiescent current sensor configured to sense quiescent current draw of the process device. Diagnostic circuitry determines a diagnostic condition of the process device as a function of the sensed quiescent current.

Abstract: A transmitter comprises a housing, an electronics assembly, an inner cover, and an outer cover. The electronics assembly includes an actuatable switch and fits within an open-ended cavity in the housing. The inner cover is positionable over the open end to cover the electronics assembly and has a deflectable button portion which is alignable with the actuatable switch and accessable from the open end while the electronics assembly is energized. The inner cover is electrically conductive and has a sleeve which frictionally mates with electrically conductive walls of the housing to shield the electronics assembly from electromagnetic interference (EMI). The inner cover is preferably an insulating molded plastic part with a thin metallic coating.