In a solid state level control with two probes, what function does the second probe serve?

In a solid state level control system using two probes, the second probe plays a crucial role in maintaining the safe operation of the equipment, specifically by serving as a low water cutoff control function.

The primary function of the first probe is to monitor the level of water in the boiler or tank. Once the water level reaches the probe, it signals that there is sufficient water. The second probe acts as a safety measure; it is positioned at a lower level and becomes active when the water drops below this point. When the second probe detects low water levels, it sends a signal to the control system to shut down the operation of the boiler or equipment to prevent damage that can occur from overheating or dry firing. This functionality is critical for maintaining equipment safety and ensuring operational reliability.

While other options involve different functions such as temperature measurement, pressure regulation, or automatic filling, they do not specifically pertain to the role of the second probe in a dual-probe level control system focused on water levels. The design and purpose of the second probe center around preventing hazardous conditions which can arise from insufficient water levels, emphasizing its role in low water cutoff control.