Guide to Correctly Calibrating Oxygen Sensors

Choosing the Correct Sensor

Here at Sensoronics, we offer many compatible replacement oxygen sensors for medical use. Medical oxygen sensors are optimized to be used with ventilators, oxygen analyzers, incubators, and anesthesia machines. The quickest way to find the correct replacement sensor for your application is to search by the original manufacturer part number. If you need assistance during regular business hours, our sales team is here to help. You can view our Medical Oxygen Sensor page here.

Conditions for Calibrating Gas Sensors

After you've chosen and received the correct oxygen sensor for your device, it is important to install it carefully and according to the instructions given by the original equipment manufacturer. As a basic premise, oxygen sensors should be calibrated in the environmental conditions that will be seen when the equipment is monitoring the patient. Environmental conditions like temperature, humidity, and atmospheric pressure will affect the output of the sensor. Always allow a sensor to adjust to room temperature before attempting calibration.

In addition, moving equipment from one location to another also requires recalibration. A piece of equipment with a sensor calibrated at sea level at 35 degrees C and 95% relative humidity should be recalibrated before being used at 8,000 ft elevation where there is reduced temperature, pressure, and humidity.

In general, oxygen sensors should be calibrated at 100% O2 rather than at room air. Room air consists of 21% oxygen and a 1% error at room air could result in a 5% error at 100% O2. On the other hand, a 1% error at 100% O2 would only result in a .2% error in room air.

Calibrating Oxygen Analyzers

Oxygen analyzers usually come with one of two different types of sensors, internal, or external. Analyzers with internal sensors generally have a barb protruding from the case where a known oxygen concentration can be applied via oxygen tubing and the instrument can be calibrated at 100% O2. Analyzers with external sensors generally have the sensor at the end of a coiled wire. The sensor can be plugged into an oxygen T-piece in an oxygen circuit and can also be calibrated at 100% O2.

Where clinical equipment is not available for calibration, analyzers can also be calibrated at 100% O2 using the following method:

  • Turn on the analyzer with the sensor connected and place the analyzer and the sensor inside of the plastic bag.
  • Place the tubing from your oxygen source in the mouth of the bag and tape it tightly so that no oxygen can escape from the mouth of the bag.
  • Using a pin, poke a number of small holes in the top of the plastic bag.
  • Adjust the oxygen flow so that the bag inflates and oxygen can be felt coming from the holes in the top of the bag.
  • Wait for the reading on the analyzer to stabilize before pushing the 100% calibrate button or adjusting the thumbwheel to a 100% reading.
  • After calibrating the instrument, turn off the oxygen and remove the analyzer and sensor from the bag. The oxygen reading should drop to 21% in room air.

Calibrating Anesthesia Machines

Certain anesthesia machines utilize sensors with a microamp output. Sensors such as our SS-10A and SS-14A generate a current when exposed to oxygen. These sensors have a conductive rubber pad short circuiting the electrodes on the bottom of the sensor. Special care should be taken when installing these sensors and the sensor should be placed in the sensor holder immediately after removing the conductive pad. If the sensor is not placed into the sensor holder immediately, the sensor will become oxygen saturated and will be unable to be calibrated for a lengthy period of time.

How Long do Oxygen Sensors Last?

The longevity of oxygen sensors is dependent on the amount of lead anode material in the sensor and the rate of oxygen consumption of the sensor. The lifetime of a sensor is generally expressed in vol.% hours. Since room air has an oxygen percentage of 21%, an oxygen sensor stored in a room air environment and rated at 250,000 vol.% hours will last approximately 1.4 years. Oxygen sensors stored in a 100% O2 environment will last approximately one fifth as long as the concentration of oxygen at 100% is five times that of room air.

What is the Shelf Life of O2 sensors?

We don't recommend storing your oxygen sensors on the shelf for more than 6 months. If the sensor can has been sitting on the shelf for longer than 6 months, it may not calibrate correctly when opened.