Boiler level control, three-pulse, two-out-of-three logic, interlock operations for high and low level conditions.

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I have a problem with the level control of the boiler drum and would like to ask the experts: 1. Is three-element control standard for boilers of all sizes in China, and is performance necessarily worse when single-element control is used?； 2. The boiler drum has three level transmitters. Generally, it is said that a “two-out-of-three” selection method is used; however, in reality, some systems use the median value while others use the average value. If one of the transmitters fails, should a “maximum or minimum of two” approach be adopted, or should it switch to using the average value instead? 3. When the drum water level is very high (extremely high), can the feed water pump be stopped? If it’s a false water level, it might not be possible to stop the pump at that point, resulting in the boiler drying out ； 4. When the drum water level is very low, there is a risk of the boiler drying out; should we consider stopping the combustion process, for example by shutting down the induced draft fan to carry out a shutdown procedure?