Abstract: A field device includes process communication circuitry configured to communicate in accordance with a process communication protocol. A controller is coupled to the process communication circuitry. The controller includes timing circuitry and is configured to generate periodic time signals during an operational period of the field device and store an indication of operational time based on the periodic time signals in non-volatile memory. The controller is configured to employ the process communication circuitry to provide an indication of operational time to a remote device.

Abstract: A field device includes process communication circuitry configured to communicate in accordance with a process communication protocol. A controller is coupled to the process communication circuitry. The controller includes timing circuitry and is configured to generate periodic time signals during an operational period of the field device and store an indication of operational time based on the periodic time signals in non-volatile memory. The controller is configured to employ the process communication circuitry to provide an indication of operational time to a remote device.

Abstract: A field instrument includes an input circuit having a transistor bridge rectifier which is couplable to a power supply. The transistor bridge rectifier is configured to provide power from the power supply to a remainder of the field instrument.

Abstract: A microcomputer based fault detector for identifying a phase reversal, a phase loss, and a power loss in three-phase circuits. A microcomputer samples a pattern of timing signals generated in response to three current transformers associated with each of the three phases. The changing pattern of timing signals represent the phase relationship of each of the three phases. The sampling rate of the microcomputer is synchronized to the alternating current in each of the three phases by an interrupt signal indirectly generated by one of the phases. In the absence of current in this interrupt generating phase, a backup interrupt, internal to the microcomputer, is enabled which directs the microcomputer to determine if the absence of the first interrupt is due to a phase loss or a power loss. Either interrupt prompts the microcomputer to sample the pattern of signals and compare it to a predetermined pattern.

Abstract: This controller is used for controlling a centrifugal compressor along its path of minimum power consumption while avoiding a surge condition. It is especially useful in a refrigeration system having a variable speed centrifugal compressor with adjustable inlet guide vanes. In such an application, the controller opens the inlet guide vanes enough to satisfy the cooling demand and then, to minimize power consumption, reduces the speed of the compressor while further opening the vanes (compensating for the reduced speed) until either the inlet guide vanes are fully open or an impending surge condition is detected. The onset of a surge condition is detected by monitoring motor current fluctuations. When fluctuations above a predetermined amplitude occur in excess of a predetermined frequency, the controller determines that a surge is impending.