General Calibration Information
All Gas Sensors will require periodic calibration to ensure your gas measurements are accurate and correct. Different gasses, and sensor manufactrers will have differeing requirements and methods for calibration. This page will serve to provide general calibration information and links to specific calibration procedures from the sensor manufacturers we represent.
Should you have any questions about sensor calibration, or would like us to help you with your calibrations please contact us.
Most sensor manufacturers will recommend calibration annually. This would be the longest interval Gas Sensing would recommend for gas sensor calibration.
Frequency of calibration will be depending upon the gasses mesaured, sensor type, and purpose of the gas sensor.
Our general recommendation would be to perform a bump-test of the sensor at least monthly. Perform a field or factory calibration or sensor check every 6-months, and a factory calibration or sensor replacement every 12-months.
NIST (National Institute of Standards and Technology)
Have you ever wondered who ensured 1 pound is exactly 1 pound? and 1 meter is precisely 1 meter? The NIST is the answer. this is the governing board that will hold the standard of measurement.
Every gas measurment calibration standard must be directly traceable to the NIST to ensure your sensors calibration is accurate. When you are reviewing your calibration certificate it must be clearly stated that the calibration standard used to calibrate your sensor is NIST traceable. If necessary, you can, and should request the proper documenation to validate that traceablity.
Calibration gasses are used to calibrate many gas sensors. Known quantities of gas can be mixed with air to provide a span calibration gas to be used for calibration. For example. if you are calibrating a chlorine sensor and would like to perform a span gas calibration at 5 ppm, you would purchase a cylinder of air mixed with exactly 5 ppm of chlrorine. This gas can be used according to the manufacturars specifications to perform a span gas calibration.
Zero gas cylinders are also avaialbe. This will ensure that pure air, that should read 0 ppm for your sensor can verify the zero setpoint of your sensor.
Note: some calibration gasses will have an expiration date, as the gasses contained may break down over time. Be careful to check this and ensure your calibration gas cylinder is not past the expiration date recommended by the manufacturer.
Not all gasses are available in a cylinder as they may have a very short half life. Ozone is the best example of a gas that must be produced on site in known quantities to perform calibration. The only option for precise ozone gas sensor calibration is sending your sensor to a facility that has a specially build calibration chamber.
Field calibration is just what it indicates. Any calibration of a sensor performed in the field, or where the sensor is currently installed. This can be performed with calibration gasses, or with devices designed to produce gasses that will react properly to ensure calibration is accurate on your sensor.
Field calibration is convenient for applications where many sensors are installed and would be challenging or inconvinient to send away for calibration. Field calibration of your sensors can be performed by Gas Sensing, and many other service companies that will calibrate, and repair your sensors.
What is Bump Testing?
When you want to know if your sensor is responding a bump test is a great option. This is simply a test that exposes the sensor to the specific gas it is intended to measure and ensure that the sensor does indeed resond. While not a precise process, this does ensure that the sensor is indeed responding and can respond in a critical situation where human safety is critical.
ATI offers an Auto-Test generator for many of the sensors used on the D12 and F12 monitors. This auto-test generator will produce a gas that cause the proper sensor to react. A test is run on a pre-set schedule, if the gas sensor does not respond as expected an alarm will come on indicating the sensor has failed. This is a great option for gas sensing is critical applications.
Note: A bump-test is not an acceptable replacement for sensor calibration
Bump Testing vs Calibration
Bump testing is a great method to ensure your sensor is responding to the gas it is intended to measure. Bump testing is not a replacement for calibration.
Calibration verifies that the sensor is accurate and providing correct measurements.
Zero calibration ensured the sensor is reading an accurate 0, or pure aire situation. Most sensors have an easy way to reset the zero in the event that it drifts over time.
Span calibration is ensuring the actual measurement of gas is accurate. The span should be done at a level of gas that would normally be measured. Create a known amount of gas at a specific level and verify the sensor displays the same level of gas.
A calibration certificate is provided by the manufacturer when you purchase a sensor. The calibration certificate provides you with the necessary information to prove that the sensor was calibrated to an NIST standard. The Calibration Certificate will provide the date the sensor was calibrated, and the date calibration should be done again.
Analytical Technologies Incorporated (ATI)
Calibration information on ATI sensor
Aeroqual handheld sensors, and fixed mount sensor heads can be calibrated using the Series-300, or Series-500 base and R42 Calibrator.
EcoSensors devices have a variety of options for calibration. We provide necessary information at the link below: