Instrumentation classification: Which of the following is not a composition-measuring instrument used for gas or liquid analysis?

Introduction / Context:
Process analyzers measure composition to ensure quality, safety, and control. Common technologies include thermal conductivity, mass spectrometry, electrochemical methods, and spectroscopies. Distinguishing true composition analyzers from flow/velocity instruments avoids misapplication.

Given Data / Assumptions:

• We are considering instruments commonly used in process or lab environments.
• “Composition-measuring” means reporting concentration or species identity/ratio.
• All options are real instruments but have different primary functions.

Concept / Approach:
A thermal conductivity cell measures bulk gas composition by relating conductivity to species fractions (e.g., binary mixtures like H2/N2). A mass spectrometer separates ions by mass-to-charge, providing highly resolved composition. A polarograph (voltammetry) measures current–potential behavior to quantify electroactive species. A hot wire anemometer, however, measures fluid velocity by heat transfer from a heated wire; it does not directly report chemical composition.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer datasheets and textbooks list hot wire anemometers under velocity/flow diagnostics, not analyzers.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming any “electrical output” device measures composition; many sensors output signals for non-compositional variables like flow or temperature.

Final Answer:
Hot wire anemometer