CURRENT LOOP INPUT PROTECTION

摘要

A protective circuit for a process control device such as a valve actuator, for example, prevents damage to device components. In particular, a protective circuit allows an analog current loop (e.g., 4-20 mA) to provide to a device 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 device 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.

主权项

1. A protective circuit in a process control device for protecting a component of the process control device, the protective circuit comprising:
a current loop input operable to receive a current proportional to an indicated value; an operating voltage input configured to couple to a voltage source and to receive from the voltage source a primary voltage signal, the operating voltage input further operable to power the component such that the process control device operates to control a process according to the indicated value; and a plurality of protective circuit components configured to:
provide a secondary voltage signal to the component from the current loop input when the primary voltage signal is below a first threshold, andprovide the primary voltage signal to the component from the operating voltage input when the primary voltage signal is above the first threshold.