16. What happens if the specified maximum load is exceeded?

The "maximum load" specifically refers to whether the sensor can maintain a linear response and recover quickly after being exposed to the target gas for more than 10 minutes. As the load increases, the sensor will gradually exhibit non-linear responses and require longer recovery times, as the sensing electrode cannot consume all diffused gas.

With increased load, gas accumulates inside the sensor and diffuses into internal spaces, potentially reacting with the counter electrode and altering the potential. In this case, the sensor may take a long time (days) to recover even when placed in clean air.

Another role of the circuit design is to ensure the sensor recovers as quickly as possible from high loads, as the amplifier in the circuit does not cause current or voltage saturation during signal generation. If the amplifier does limit current into the sensor, this will restrict the rate at which the sensing electrode consumes gas, immediately causing gas buildup inside the sensor and the potential changes described above.

Finally, select a resistor connected to the sensing electrode to ensure that even with sudden voltage drops at the foreseeable highest gas concentration, the change does not exceed a few millivolts. Allowing larger voltage drops across the resistor could cause similar changes in the sensing electrode, requiring recovery time after the gas is removed.

17. How much oxygen is required for the sensor to function properly?

Sensors that generate output by oxidizing the target gas (e.g., carbon monoxide sensors) require oxygen at the counter electrode to balance the oxygen consumed by the oxidation reaction. Typically, a maximum of several thousand ppm of oxygen is needed, which is provided by the oxygen in the sample gas. Even if the sample gas is oxygen-free, the sensor has sufficient internal oxygen supply for short periods.

For most sensors, the counter electrode also requires a small amount of oxygen. If the sensor continuously operates in an oxygen-free environment, it will eventually produce erroneous readings.

18. Why is the sensor reading lower than specified?

There are many reasons for discrepancies in customer measurements, making it crucial to design equipment based on the sensor’s allowable calibration range and the natural decline in output capacity over its service life. Some causes we have identified include:

• Using different flow rates

• Placing additional diffusion grids (e.g., flame arrestors or PTFE membranes) in front of the sensor, especially if there is a large dead space between the grid and the sensor

• "Sticking" gases with absorbent tubing or brass calibrators (e.g., gas cylinders contaminated by chlorine; nitrogen cylinders degraded by oxygen ingress)

• Using cylinders outside the manufacturer-recommended minimum pressure

• Using "air" cylinders with diluted mixtures

• Failing to properly dampen pressure fluctuations in the sample system

• The design of the test device significantly affecting the measurement signal of combustible gas sensors

19. How to connect the sensor?

Sensors are typically connected to equipment via PCB connectors. Some sensors use alternative connections (e.g., data ports or specific connectors); refer to the relevant product data sheets for details.

For sensors connected via PCB connectors, do not directly solder the PCB connector to the equipment. Direct soldering may cause damage to the product housing and invisible internal damage.

20. Is temperature data available?

Temperature data is available for most products and is specified in each product data sheet.

21. What is the recommended shelf life?

The maximum recommended shelf life for sensors is six months. During this period, sensors should be stored in a clean, dry container at 0°C to 20°C, not in environments with organic solvents or flammable liquids. Under these conditions, sensors may be stored for up to six months without reducing their expected service life.

22. Why is there a minimum flow rate requirement?

The minimum flow rate requirement for sensors is comprehensively determined by design principles, medium characteristics, measurement accuracy, and practical application needs. When selecting and using sensors, users should choose appropriate sensor types and flow rate ranges based on specific application scenarios and measurement requirements.