Troubleshooting of Four-in-One Gas Detectors
A 4-in-1 gas detector is a device flexibly configurable for single or multiple gas measurements. It can be fitted with an oxygen sensor, a flammable gas sensor, toxic gas sensors, any combination of four gas sensors, or a single gas sensor as required. Equipped with a large clear LCD screen with backlight, as well as audible, visual and vibration alarm functions, it can detect hazardous gases and send timely alerts to operators for preventive measures even in harsh working conditions.
The detection principle of the 4-in-1 gas detector works as follows: when the concentration of measured flammable gas exceeds the threshold, the amplified bridge output voltage is compared with the preset reference voltage in the circuit via a voltage comparator. A square wave generator then outputs square wave signals to trigger the sound and light alarm circuits. The buzzer emits continuous beeps and the light-emitting diodes flash to deliver warning signals. As inferred from its working principle, electromagnetic interference will distort detection signals and lead to reading deviations; collisions and vibrations may cause circuit open circuits and result in detection failure; excessive ambient humidity or water ingress into the unit can trigger short circuits or changes in line resistance, further causing detection malfunctions.
Formaldehyde is a colorless, water-soluble and irritant gas. Its primary indoor sources include wood-based panels such as particleboard, medium-density fiberboard and plywood, adhesives and wallpaper, with a release cycle lasting 3 to 15 years. It is absorbed through the respiratory tract and poses long-term, latent and hidden health risks to the human body. Long-term inhalation of formaldehyde may induce severe illnesses including nasopharyngeal carcinoma and laryngeal cancer.
For example: when formaldehyde comes into contact with test paper, the reagent impregnated in the paper reacts with formaldehyde to form a compound, turning the paper from white to yellow. The degree of color change reflects the intensity of reflected light. The rate of variation in reflected light intensity serves as the response value corresponding to gas concentration. By pre-calibrating the standard curve, the concentration of the target gas can be calculated based on the measured response value.
The 4-in-1 gas detector consists of two core modules: measurement and detection, with corresponding functional modules for both. The measuring principle relies on a detection bridge circuit composed of the sensor's detection element, fixed resistors and a zero-adjustment potentiometer. The bridge uses platinum wire as the carrier for the catalytic bead component. When powered on, the platinum wire heats up to its operating temperature, and ambient air reaches the component surface through natural diffusion or forced sampling. When no flammable gas is present in the air, the bridge outputs zero voltage. If flammable gas diffuses onto the detection element, flameless catalytic combustion occurs, raising the element temperature and increasing the resistance of the platinum wire. This unbalances the bridge and generates an output voltage proportional to the flammable gas concentration. The voltage signal is amplified, converted from analog to digital, and finally displayed on the liquid crystal screen as the measured gas concentration value.
