What is the primary function of a computing relay in a three element feedwater control system?

The primary function of a computing relay in a three element feedwater control system is to compare outputs from steam and water flow transmitters. This comparison is crucial because it allows the control system to manage the feedwater flow rate in response to the actual steam demand of the system.

In a three-element control loop, the computing relay processes signals from three main inputs: the flow of steam out of the boiler, the flow of water into the boiler, and the water level within the boiler. By comparing the flow outputs, the computing relay can adjust the feedwater supply to ensure that the boiler remains at optimal pressure and level, thus improving efficiency and preventing issues such as low water conditions that could lead to boiler damage.

In contrast, measuring steam pressure fluctuations, adjusting steam flow directly, and regulating the furnace temperature, while important aspects of a boiler system, do not represent the primary function of the computing relay within this specific feedwater control application. The relay's task is focused on maintaining the delicate balance between steam generation and water supply.