Current loop input protection
AssigneeFisher Controls International LLC
InventorClyde T. Eisenbeis
Life of this patent
Estimating the term…
Abstract
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.
Claims15
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, separate from the current loop 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, and
- provide the primary voltage signal to the component from the operating voltage input when the primary voltage signal is above the first threshold.
A process control device comprising:
- an integrated circuit component;
- an operating voltage source coupled to a voltage input of the integrated circuit component to provide a primary voltage signal to the integrated circuit component;
- a protective circuit including a current loop input, separate from the voltage input, the protective circuit 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, and
- provide the primary voltage signal to the component from the operating voltage source when the primary voltage signal is above the first threshold.
Dependencies are inferred from the claim text.