Telemetering and Surveillance Monitoring of Process Control Signals

Abstract

The advent of electronics into process control resulted in the collection of the process monitoring and control hardware at a centralized location. This approach while improving the system maintainability and operational safety, brought with it the new problem of Intercommunication with the process. The Centralized System has to receive signals from the measuring sensors which measure physical quantities like temperature, pressure, flow, level etc. and output signal to feed the final actuators. A typical system requires the Telemetering of hundreds of measurement and control signals over several thousand meters apart from all important man-machine communication links.

These signals have to traverse harsh electrical environments typical of process industries without their fidelity being affected. This led to a variety of signals standards to be used, culminating in the current international standard of 1 to 5 V for voltage signals and 4 to 20 mA for current signals. Both these signals have their pros and cons and only a proper blend of these two signals can produce a cost effective telemetering scheme for maximum plant safety and control reliability.

This paper brings out the typical telemetering schemes to be employed with an electronic process control system for maximum safety and reliability. It also discusses how the surveillance monitoring of these signals increases system availability and maintainability.