Common Questions and Answers About Sensors 1
Views：210 Updated：2025-06-23
1. How often does the sensor need to be recalibrated?
The interval between initial calibration and recalibration depends on multiple factors, including the sensor’s operating temperature, humidity, pressure conditions, the types of gases it is exposed to, and the duration of exposure.
2. How significant is the difference in cross-interference?
The degree of cross-interference variation can be quite substantial. This is evaluated based on tests of a limited number of sensors, which measure the sensors’ responses to non-target gases rather than the target gases themselves. It is important to note that when environmental conditions change, the sensor’s performance may differ, and cross-interference values may vary by up to 50% between different batches of sensors. Therefore, in practical applications, these variables should be fully considered for the sensor’s accuracy and reliability.
3. Will using a pump in front of the sensor accelerate the reaction?
Using a pump does not speed up the sensor’s own reaction rate, but it can rapidly and efficiently draw gas samples through the sensor from inaccessible locations. This allows the pump to influence the overall response time of the device.
4. Can a film or filter be added in front of the sensor?
A film or filter can be placed in front of the sensor for protection, but it must ensure that no "dead space" is created, which could prolong the sensor’s response time.
5. What factors should be considered when designing a suitable sample system?
When designing a sample system, it is critical to use materials that prevent gas adsorption on the system’s surfaces. The best materials include polymers, PTFE, TFE, and FEP. Gas concentration may cause moisture condensation, which can block the sensor or lead to overflow, so appropriate dehydrators should be used—such as Nafion tubing to remove moisture at the condensation stage. For high-temperature gases, the sample gas should be cooled to meet the sensor’s temperature requirements, and appropriate filters should be used to remove particulate matter. Additionally, axial chemical filters can be installed in the sample system to eliminate cross-interference from gases.
6. What happens if the temperature of the gas itself is different from that of the sensor?
The sensor's own temperature determines its minimum display current, and the temperature of the measured gas sample has a certain influence on this. The rate at which gas molecules enter the sensing electrode through the pores determines the sensor's signal. If the temperature of the gas diffusing through the pores differs from the temperature of the gas inside the sensor, it may affect the sensor's sensitivity to some extent. Slight drift or momentary current changes may occur before the device is fully set up.
7. Can the sensor be continuously exposed to the target gas?
Oxygen sensors can continuously monitor oxygen concentrations within a range of 0-30% by volume or partial pressures within a range of 0-100% by volume. Toxic gas sensors are typically used for intermittent monitoring of target gases and are not suitable for continuous monitoring, especially in environments with high concentrations, high humidity, or high temperatures. To achieve continuous monitoring, a method of cycling two (or even three) sensors is sometimes used, allowing each sensor to be exposed to the gas for a maximum of half the time and recover in fresh air for the other half.
8. What materials are used for the sensor housing?
We use different plastic materials considering compatibility with the internal electrode system and application durability requirements. Commonly used materials include ABS, polycarbonate fiber, or polypropylene. More detailed information can be found in the data sheet of each sensor.
9. Is the inside of the sensor safe?
Although there is no certificate proving its intrinsic safety, the product can stably meet the requirements for internal safety.
10. How to test the circuit?
Three-electrode and four-electrode sensors are suitable for use in a special circuit called a Potentiostat. The purpose of this circuit is to control the potential of the sensing (and auxiliary) electrode relative to the counter electrode while amplifying the current flowing in or out. The circuit can be tested using the following simple method:
? Remove the sensor.
? Connect the counter terminal to its corresponding terminal with the circuit.
? Measure the potential of the sensing (and auxiliary) terminal. For a non-biased sensor, the test result should be 0 (±1mV), which is equivalent to the recommended offset voltage for a biased sensor.
? Connect the sensing (or auxiliary) terminal with the circuit to obtain the output voltage.
The above steps can confirm that the circuit is operating normally in most cases. After replacing and re-fixing the sensor, the voltage between the sensing and reference terminals of a non-biased sensor should still be zero, or equivalent to the recommended offset voltage of a biased sensor.
In most cases, the above steps can confirm that the circuit is operating normally. After replacing and re-fixing the sensor, the voltage between the sensing and reference electrodes of a non-biased sensor should be close to zero, or equivalent to the recommended offset voltage of a biased sensor.
Generally, Sensors cannot be cleaned in a typical cleaning system without causing irreversible damage or affecting their monitoring performance. High pressure and temperature will damage their sealing, and active chemicals such as ethylene oxide and hydrogen peroxide may destroy the electrocatalyst.
11. What happens if I expose the sensor to temperatures outside the specified operating instructions?
In terms of mechanism, low temperature generally is not a major issue. The liquid electrolyte in all sensors (except oxygen sensors) does not freeze until the temperature drops to around -70°C. However, long-term exposure to excessively low temperatures may affect the fixing of the plastic housing on the bracket.
For oxygen sensors, although high salt content means they may not be damaged immediately, the oxygen sensor electrolyte freezes at approximately -25 to -30°C, which may eventually lead to sensor failure.
Temperatures exceeding the upper limit will put pressure on the sensor's seal, eventually leading to electrolyte leakage. The plastics used to manufacture most sensor models become soft when the temperature exceeds 70°C, rapidly causing sensor failure.
12. What happens if I expose the sensor to pressures outside the specified operating instructions?
All sensors use similar sealing systems, where the hydrophobic properties of PTFE materials prevent liquid from flowing out of the sensor (even with air holes). If the pressure applied to the sensor inlet suddenly increases or decreases beyond the allowable internal limits, the sensor's membrane and seal may deform, causing leakage. If the pressure changes slowly enough, the sensor may operate beyond the pressure tolerance, but consult technical support for advice.
13. What are the ideal conditions for storing sensors?
Sensors stored in their original packaging typically do not deteriorate significantly even beyond the shelf life. For long-term storage, we recommend avoiding hot environments, such as windows exposed to direct sunlight.
If sensors are removed from their original packaging, keep them in a clean place and avoid contact with solvents or heavy smoke, as smoke may be absorbed into the electrodes, leading to operational issues. Oxygen sensors are an exception: once installed, they begin to be consumed. Therefore, they are transported or stored in sealed packages at reduced oxygen levels during unloading.
14. What are the power requirements for sensors?
Two-electrode sensors, such as oxygen sensors and two-electrode carbon monoxide sensors, generate electrical signals through chemical reactions and do not require an external power source. Three-electrode and four-electrode sensors, however, must use a potentiostatic circuit and therefore require a power supply. In fact, the sensor itself still does not need power because it directly produces output current through oxidation or reduction of the target gas, but the circuit amplifier consumes some current—though this can be reduced to very low levels if necessary.
15. How long do built-in filters last?
Some sensors have built-in chemical filters to remove specific gases and reduce cross-interference signals. Since the filter is placed behind the diffusion grid, and gas entry through the grid is much less likely than through the main gas channel, small amounts of chemical media can last a long time.
In general, the filter and sensor have a comparable expected lifespan for the required application, but in harsh conditions (e.g., emission monitoring), this may be challenging. For such applications, we recommend sensors with replaceable built-in filters, such as the Series 5 sensors.
For some pollutants, the filter does not remove them through chemical reactions but by adsorption, making it easy for the filter to be overwhelmed by high concentrations—organic vapors are a typical example.
