What is the purpose of zero and span checks on gas analyzers?

• A. Zero checks verify baseline; span checks calibrate the instrument response to a known concentration across the measurement range.
• B. Zero checks calibrate to known positive concentration; span checks adjust equipment power.
• C. Zero checks verify baseline; span checks calibrate to a random concentration.
• D. Zero checks adjust sampling frequency; span checks adjust sample flow.

Answer: (A)

Zero and span checks are calibration steps used to ensure gas analyzers read accurately. A zero check uses a zero gas (clean air or inert gas) to establish the baseline response when the target gas is not present, removing any sensor offset or electronic drift. A span check uses a gas with a known concentration to calibrate the instrument's response, establishing the correct slope so readings across the measurement range correspond to real concentrations. Together they verify accuracy, detect drift or sensor aging, and ensure the analyzer can quantify concentrations reliably. The other options mix up the roles: zero checks don’t set a positive concentration, span checks don’t adjust power, span checks aren’t for random concentrations, and zero or span adjustments for sampling frequency or flow are not their purpose.