Current Loop Input Protection

摘要

A component in a process control device such as a valve actuator, for example, is coupled to a protective circuit. In particular, the protective circuit allows an analog current loop (e.g., 4-20 mA) to provide to the 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 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 component in a process control device, the component comprising:
a first input receiving a signal from a current loop; and a second input, different from the first input, receiving a signal from a voltage source, wherein the component is coupled to a protective circuit that, when the signal from the voltage source is below a first threshold, provides to the second input a backup voltage signal derived from the signal received at the first input.