What is the primary purpose of a calibration gas in instrument calibration?

• A. To provide a known concentration reference for zero and span adjustments.
• B. To provide a variable reference for adjustments.
• C. To test the instrument's power supply.
• D. To verify flow rate accuracy.

Answer: (A)

Using a calibration gas provides a stable, known concentration reference that lets you set the instrument’s zero and span. The zero adjustment uses a gas with essentially no target contaminant to establish the baseline signal, while the span adjustment uses a gas with a defined concentration to set the instrument’s response across its measurement range. This pairing ensures the readings are accurate and traceable, even as sensors drift over time. Calibration gas isn’t meant to test power supplies or flow meters, which require separate checks and tools. Its key role is giving a reliable, reproducible reference so the instrument reports true concentrations.