A performance-stable carbon monoxide alarm can consistently make correct decisions and responses according to the regulatory “time-concentration model” throughout its 10-year lifespan.
If you want to design a performance-stable CO alarm, you must solve the CO sensor stability.
What is CO sensor？
The CO sensor is an electrochemical sensor with characteristics like those of a fuel cell.
When CO is present, the CO sensor generates a current output that is approximately linearly proportional to the CO concentration.
The relationship is: 1.2nA～2.5nA/PPM(CO)
- Rs is the series equivalent resistance of the CO sensor.
- C is the parallel equivalent capacitance of the CO sensor.
- Ig is the current source linearly related to CO concentration.
- Rp is the parallel equivalent impedance.
How is CO sensor working？
When carbon monoxide (CO) gas diffuses through the gas pores in the casing and the permeable membrane (Carbel) to the surface of the working electrode (MEA), it undergoes an oxidation reaction with water on the working electrode (MEA) under the catalytic action of platinum (Pt). The chemical reaction is as follows:
CO+H2O → CO2+2H+ + 2e–
The oxidation reaction occurring at the working electrode produces H+ ions and electrons (e-). The H+ ions are transferred through the proton exchange membrane to the counter electrode, where, under the action of a catalyst, they react with oxygen in a reduction reaction to form water. The chemical reaction equation is:
O2+4H++4e–→2H2O
In other words, a reversible oxidation-reduction reaction occurs inside the sensor. The chemical reaction equation is:
2CO+2O2 → 2CO2
Figure 2 shows this reversible oxidation-reduction reaction continuously occurs between the working electrode and the counter electrode, generating a potential difference between the electrodes. Based on the direction of the positively charged H+ ion transfer, the gas inlet end plate can also be considered the negative electrode and the casing the positive electrode.
When the CO sensor dimensions produce an output current, its magnitude is directly proportional to the gas concentration. By measuring the magnitude of the sensor’s output current through its pins using an external circuit, the concentration of carbon monoxide (CO) can be detected, and a wide linear measurement range is achieved. Therefore, by connecting an external signal acquisition circuit and corresponding conversion and output circuits to the gas sensor, it is possible to detect and monitor carbon monoxide (CO) gas.
How is a CO sensor structure composed?
There are 8 parts composed of a CO sensor, there are:
- Metal Can
- Bottom Plate
- Large Carbel
- MEA（Membrane electrode assembly）
- White Rubber Ring（ Secures the Carbone/MEA position）
- Small Carbel
- Face Plate
- Sealing Ring
What is the meaning of stableperformance?
In the field of carbon monoxide (CO) sensors, “stable performance” refers to: under specified operating conditions and within a given time frame, the drift of key sensor parameters (sensitivity, zero-point, response speed, etc.) remains consistently within the standard allowable range, enabling continuous and reliable output of accurate measurement voltage or current values.
What are the key indicators for measuring stability?
There are four factors impacting electrochemical CO sensors.
Parameter | Definition | Stability Requirements |
|---|---|---|
Zero Drift | Change in sensor output over time/temperature and humidity in the absence of CO | ≤±2% FS/year, or ≤±1-2 ppm/month |
Sensitivity Drift | Rate of change in indicated value/output signal when exposed to standard CO gas | ≤±2%~±5% of reading/year |
Response Time Stability | Change in T90 (time to reach 90% of the final value) | T90 is typically ≤60s, with an increase of ≤30% over its lifespan |
Temperature/Humidity Stability | Indicated value error during temperature and humidity changes | within -10~50℃, the error is ≤±5% of reading |
How about the CFS CO sensor performance?
Parameter | CFS CO Sensor Performance |
|---|---|
Target gas | carbon monoxide (CO) |
Test gas range | 0~5000 PPM |
Output current | 1.2~2.5nA/PPM |
Nonlinear | 5%（in 0~1000PPM） |
Operationtemperature | -10˚C ~ +55˚C (prefer) -20˚C ~ +60˚C (option) |
Operation humidity | 5%~95%（No condensation） |
Response time | <50s |
Lifespan | 10 years |
You can easily contact CFS experts for a free design of the CO sensor circuit and customize your sensor with different sensitivity and size according to your requirements.
How to control key parameters in CFS CO sensor production?
There are two key parameters such as sensor capacitance, sensor series impedance Rs,Sensor output at 0/100/400 PPM CO gas, and sensor parallel impedance Rpto control in sensor production.
How does CFS produce CO sensors?
CFS produces CO sensors, mainly including incoming inspection, incoming material cleaning, housing clamping, electrolyte injection, component assembly, seal ring installation, crimping and sealing, aging test, CO testing, lead welding& laser.
1. Incoming material cleaning
2. Housing clamping
3. Electrolyte injection
4. Component assembly
5. Seal ring installation
6. Crimping and sealing
7. Aging test
8. CO testing
9. Lead welding& laser logo
10. Packaging
Summary
A performance-stable CO alarm is not designed to “detect CO well one time”, but to “make the right alert for 10 years”.
CFS provide one stop ODM/OEM solution for your sensor.
