The Medical Oxygen Sensor Working Principle and Performance Test

The o2 cell for the ventilator, called the medical oxygen sensor, is an essential part of the ventilator. It is between the patient inhaling connector and Air Oxygen Mixer. The oxygen sensor acts as a monitor in the ventilator to measure oxygen concentration in the mixed air and has no relation with the oxygen level. The measurement range is from 0 to 100% oxygen concentration to ensure the oxygen transformed to the patient matches with the setting and avoids oxygen toxicity because of long-time oxygen-inhaling in high concentration or life-threatening due to low concentration. Under constant pressure and temperature, the electric pressure generated by the O2 cell has a proportional relation to the oxygen concentration. It has a stable pressure output during its service time.

If the oxygen concentration level is different from the setting, the machine will issue an alarm prompt, and then it can be calibrated. The cannot-be-fixed deviation means the oxygen battery is exhausted and replaced. The oxygen sensor has a service life of about 1 to 3 years.

The O2 cell performance checking

1, Check the oxygen concentration level first.
When there is a difference between the measurement level and setting, we can check if the pressure, airflow, and oxygen concentration work well.
2, Check if the air-oxygen mixer works well.
3, Be sure it is not the problem of o2 cells and mixer. And, when there is a deviation of more than 10% with at least 30S, we can judge the oxygen sensor is out of work.

Manufacturers access the output voltage at 21% and 100% oxygen concentration (the voltage respective x and Y), then analyze if the deviation range for the x/21% and y/100% is under 5%. For example, when the oxygen in the air has an output voltage of 13.9% in 21% and 66.3% in 100%, the actual deviation is under 5% (13.9/21%=66.1%, 66.3/100%=66.3%). And because of it, the oxygen sensor is a valid one.

Also, we can use Oxygen Concentration Meter for judgment. It is a portable device with a screen and can have the oxygen concentration reading in seconds with 1%-2% precision. When we have a huge deviation, we can have the meter on the airway to test the measurement of the meter, oxygen, and the setting number to check which two are closer. It would be less than 5% in a normal working status. We can use it for fault checking.

The Calibration for Oxygen Sensor

If the measurement record has a 2% deviation for the first time, we can calibrate for the O2 cell. As a sensor, its energy consumes with the time go. The parameter is different each time we use the oxygen sensor, it would lead to the oxygen control, and the record is different. Thus, it is essential to have calibration. If the oxygen cell passes the calibration, the oxygen is still valid in use. It would have a pre-long life of about 1-4 months.

The principle for calibration

Set the oxygen concentration to 21% and 100%, and then adjust the oxygen cell to make the measurement record and setting number keep the same. If it is the same as the setting number, it usually indicates that we need to change the oxygen. Once we have calibrated the 21% and 100% concentrations, we choose another oxygen concentration number for calibration. If the deviation is under 5%, it tells us that there is no problem with the O2 cell control and monitoring. The broken o2 cell cannot pass the calibration in general. But it does not represent the cell is valid if it passes the calibration as if we only take 21% and 100% for the calibration.

Now, the ventilator has auto-calibration. Usually, it has an alarm when the oxygen cell is not in the condition with the following O2% HIGH, O2% LOW, or REPLACE O2 SENSOR.

The compatible Oxygen sensor selection：

Generally, the lifespan for oxygen cells is 1-2 years and close to 3 years for high-quality products. It is determined by the working environment. High oxygen or high-temperature working surroundings shorten its life. Considering the high price of original oxygen sensors, some hospitals choose compatible O2 cells.