Which letter is commonly used to represent the succeeding function of the instrument?

In the context of instrumentation, particularly in the fields of process control and automation, the letter commonly used to represent the succeeding function of an instrument is S. This designation is often associated with the output signal that an instrument provides after processing the input data.

For example, in control systems, the term 'successive' can refer to a signal or function that follows another in a sequence, and S is frequently used to denote this output during analyses or in graphical representations like signal flow diagrams. It helps differentiate the primary function or input from the subsequent function or output, thus providing a clear understanding of the signal flow and relationships between different components of the system.

The other letters, while they may have significance in various contexts, do not carry the same standard meaning for the succeeding function of an instrument in instrumentation terminology. S stands out as the most widely recognized representation in this context.