In instrumentation and control engineering, the term ‘‘dead zone’’ refers to the input–output insensitivity of an indicating or recording device. Which definition best captures this concept for a measurement instrument (do not confuse with time constant or pure transportation lag)?

Introduction / Context:
The “dead zone” (also called dead band) is a classic static characteristic in measurement systems. It describes a finite range of input over which the output does not respond. Understanding it helps technicians and engineers diagnose why an indicator shows no movement despite small process changes, and to distinguish it from dynamic behaviors such as time constant or transportation lag.

Given Data / Assumptions:

• We are dealing with an instrument's input–output behavior.
• Dead zone pertains to a region of no indicated response.
• Time constant and transportation (dead) time are dynamic, not static, properties.

Concept / Approach:
Dead zone is a static “insensitivity” band. If the true process variable changes within this band, the pointer, digital display, or recorder remains unchanged. Causes include mechanical friction, backlash, hysteresis, or intentional filtering to prevent flicker. The formal phrasing is “the maximum change in input that produces no output change around a specified operating point.”

Step-by-Step Solution:

Verification / Alternative check:
Calibration procedures often check for dead band by increasing and decreasing input to detect any “no-motion” span around setpoints.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing dead zone with hysteresis; hysteresis is a loop difference between increasing and decreasing inputs, while dead zone is a flat no-response region.

Final Answer:
Maximum change in the measured variable that does not change the instrument reading