Gas detection systems identify the presence and concentration of specific gases. These instruments use sensors that react to target gases, generating signals corresponding to gas concentrations. Regular calibration is necessary to ensure accurate and reliable readings. This process uses calibration gas as a reference standard to maintain detector precision, preventing inaccurate readings that could lead to hazardous situations.
What is Calibration Gas?
Calibration gas is a precisely measured, certified gas mixture used as a standard for analytical instruments like gas detectors. Also known as span gas or test gas, it establishes a known response to a certified chemical concentration. It must have a precisely defined composition and be traceable to national or international standards, linking it to primary reference materials for accuracy.
Calibration gas typically consists of a target gas, such as methane or carbon monoxide, mixed with a balance gas, often nitrogen or air. Manufacturers prepare these mixtures using methods like gravimetric analysis, ensuring high accuracy and traceability. The exact concentration of each gas, its uncertainty, and stability period are provided on a certificate of analysis.
Why is Calibration Gas Essential?
Calibration gas is essential for ensuring the reliability and accuracy of gas detection equipment, crucial for safety across industries like manufacturing, oil and gas, and environmental monitoring. Without proper calibration, gas detectors can provide inaccurate readings due to sensor drift or degradation. This can lead to risks such as undetected gas leaks, fires, explosions, or exposure to toxic substances, jeopardizing personnel safety.
Calibration gas confirms gas detector sensors respond appropriately and alarms activate at correct thresholds. This allows adjustments, maintaining accuracy as sensors age. Beyond safety, regular calibration supports compliance with industry regulations, helping businesses avoid fines or legal issues. It maintains safe working environments and prevents incidents.
How Calibration Gas is Used
Calibration gas is applied to gas detectors through a specific process. The procedure involves connecting the calibration gas cylinder to the detector using a regulator and a calibration cap or adapter. Before applying the calibration gas, the detector is “zeroed” in a clean air environment, often using zero gas like nitrogen or fresh air, to establish a baseline. This ensures the detector registers zero when no target gas is present.
After zeroing, the known concentration of calibration gas flows over the detector’s sensors for a specified duration, typically one to two minutes, allowing sensors to stabilize. The detector’s readings are compared to the known concentration, and adjustments align the instrument’s response with the expected value. This process, a full calibration, resets the sensor’s response against the known gas concentration. In contrast, a bump test is a quicker functional check that briefly exposes sensors to gas to verify response and alarm activation, without adjusting accuracy.
Key Considerations for Calibration Gas
Proper handling and storage of calibration gas cylinders maintains integrity and accuracy. Cylinders should be stored in a cool, dry, well-ventilated area, away from heat or direct sunlight, ideally between 50°F and 77°F (10°C and 25°C). Extreme temperatures can affect gas pressure and composition, leading to inaccurate calibration. Storing cylinders upright and securing them prevents falls.
Checking expiration dates is necessary, as cylinders have a limited shelf life, typically 12 to 36 months, depending on the gas mixture. Reactive gas mixtures, such as hydrogen sulfide or ammonia, have shorter shelf lives (8 to 12 months) compared to non-reactive gases like methane, which can last up to three years. Using a first-in, first-out (FIFO) system and disposing of expired cylinders according to local regulations ensures only effective gas is used. Traceability to national standards, indicated by a certificate of analysis, confirms quality and composition.