Abstract:
A process transmitter communications circuit (20, 96) has link terminals (40) which are coupled to a process link (12), which supplies power to the circuit. A power source (38) is coupled to one of the link terminals and is independent from the power supplied from the process link (12). Communications circuitry (42) is coupled to the power source (38) and link terminals (40), which transmits a transmitter signal over the process link (12), through the link terminals (40). A power sensing component (44) is coupled to at least one of the link terminals (40) and the communications circuitry (42) and senses whether the power supplied by the process link (12) is inadequate to transmit the transmitter signal. A power control component (46) is coupled to the power source (38), the link terminals (40) and the communications circuitry (42) and selectively applies power from the power source (38) to the communications circuitry (42) for transmitting the transmitter signal when the power sensing component (44) senses there is inadequate power supplied by the process link (12).
Abstract:
An existing analog two-wire transmitter (11) has a sensor module (35), and analog circuits (23) which provide an output representative of a sensed process variable, such as pressure, to a two-wire current loop (14). At least portions of the analog circuit (23) are removed and replaced with apparatus including a digital converter (52) that digitally calculates the transmitter output using the same current range in the current loop (14) and calculating corrections for obtaining linearity of the output.
Abstract:
An existing analog two-wire transmitter (11) has a sensor module (35), and analog circuits (23) which provide an output representative of a sensed process variable, such as pressure, to a two-wire current loop (14). At least portions of the analog circuit (23) are removed and replaced with apparatus including a digital converter (52) that digitally calculates the transmitter output using the same current range in the current loop (14) and calculating corrections for obtaining linearity of the output.
Abstract:
Un émetteur analogique à deux fils existant (11) possède un module capteur (35) et des circuits analogiques (23) qui envoient des signaux de sortie représentant une variable d'un processus capté, telle qu'une pression, à une boucle de courant à deux fils (14). Quelques parties au moins du circuit analogique (23) sont démontées et replacées par un dispositif comprenant un convertisseur numérique (52) qui calcule de manière numérique les signaux de sortie de l'émetteur en utilisant la même plage de courant dans la boucle de courant (14) et qui détermine les corrections permettant d'obtenir des signaux de sortie linéaires.