The range of values over which an input signal to a transmitter may be changed upon reversal of direction with no observable change in output is called:

The range of values over which an input signal can vary without producing an observable change in the output is referred to as "dead band." This concept is crucial in control systems because it defines a zone where small fluctuations in the input do not affect the output. This can occur due to mechanical play, hysteresis, or inherent limitations in the measurement system.

Understanding dead band is important for ensuring that control systems operate efficiently, as it helps identify areas where signals may change without requiring a response from the system. By acknowledging the dead band, technicians can fine-tune control parameters to improve system performance and responsiveness.

In contrast, instrument accuracy relates to the degree of closeness of a measured value to its true value, while the zero point refers to the baseline or starting point of measurement. Reverse precision is not a standard term used in control systems, making it less relevant in this context. Thus, dead band is the key term that accurately captures the described phenomenon in the operation of transmitters and control systems.