Whether you turn on a steam iron, open the bathroom door after a shower, or grill pork belly, the fire alarm rings without fail. According to a 2019 SBS report, five maintenance managers at a newly built apartment complex resigned within 10 months of residents moving in due to frequent fire alarms, and almost all of the 773 analyzed false alarms originated from smoke detectors. They recognized condensation, dust, steam, fine dust, and even steam rising from the bathroom as fires. The Fire Department's inspection concluded that the issue was a "problem with the living environment," which, to put it simply, means that currently mass-produced smoke detectors are unable to distinguish changes in the environment.

The problem is that industrial sites are far more dangerous than homes. Alarms that resemble the boy who cried wolf foster a complacency regarding safety, and when false alarms accumulate in ESS, hydrogen infrastructure, and power plant switchboards—where a single genuine signal must not be missed—even a real fire signal is easily perceived as yet another malfunction. The SJ_SMOKE family, refined over five years by SuJin, a small giant in Suwon, offers the answer to this very issue. It structurally eliminates the possibility of optical path misalignment, distinguishes between smoke and water vapor using two wavelengths, and sends real-time concentrations from 0 to 100% to the host via RS-485 Modbus RTU.

Structural limitations of existing detectors

Optical smoke detectors operate on a simple principle in which light emitted from an IR LED reaches a photodiode inside the chamber, and the amount of light is detected when smoke intervenes. The problem arises from the fact that the LED and photodiode are assembled by manually aligning them as separate components. Slight misalignments in the light path may exist from the start, and over time, the alignment becomes increasingly distorted due to the tension applied to the metal legs of the LED. This effect is accelerated in vibrating environments. Furthermore, since the simple comparator circuit can only output ON/OFF signals, there is no way to know whether the concentration is 5% or 50%, leaving the judgment of whether it is a malfunction or the actual early stages of a fire to the operator's intuition. The ionization method based on radioactive material (americium) that emits alpha rays has another problem: its response speed is noticeably slower compared to the optical semiconductor method.

Everything on a single die — the answer called ADPD188BI

The core component adopted by Sujin is the ADPD188BI from Analog Devices Inc. of the United States. It is a dedicated smoke measurement IC that integrates an IR LED, Blue LED, photodiode, and peripheral circuitry all within a single semiconductor die.

This single line encapsulates two innovations. First, the source of optical path misalignment is eliminated. Since the LED and photodiode are placed on the same silicon, manual alignment is unnecessary. The physical possibility of alignment distortion caused by vibration, temperature, or time is eliminated. Second, smoke and water vapor identification using dual wavelengths. Light scattering depends on the relationship between particle size and wavelength; smoke particles (primarily carbon and polymers ranging from 0.01 to 1 µm) and water vapor particles (relatively large water droplets) exhibit different scattering ratios across two wavelengths: IR and Blue. By comparing the response ratios of the two wavelengths, it is possible to infer whether the cause of the same amount of light blocking is smoke or water vapor. This approach resolves false alarms caused by condensation, steam, or vapor at the optical level. With the component mounting minimized and power consumption reduced, it can operate for about 50 hours with a single 24V 600mAh battery pack, and the operating temperature ranges from -40 to 85℃, covering virtually all industrial environments.

Accurate concentration + industrial communications integration

Even with high-quality components, they are meaningless if the data is coarse. Sujin processes the raw optical signals received from the ADPD188BI using its proprietary algorithm to convert them into smoke concentration values ranging from 0% to 100%. This allows for the graphing of how quickly smoke rises, rather than just simple ON/OFF switching. When a client requested a response curve that rose to 100% in 1 second and maintained it for 3 seconds, Sujin redesigned the output characteristics via firmware to match the requirements and delivered the product. The ability to produce different responses on the same hardware signifies that this is more than just a component; it represents a solution.

The data output is an RS-485 Modbus RTU slave structure. It provides smoke concentration (0x1014), temperature (0x1024), relative humidity (0x1034), and an integrated register (0x1004) that reads all three values at once. Any engineer familiar with industrial communications will be able to see at a glance the thoughtful design, including 9600bps default and readjustable, multi-drop up to 32 units with a 5-bit ID switch, 120Ω termination resistor On/Off, and simultaneous reset of ID=0 broadcast.

5 Years of Industry Validation — The Validation Curve Stears

The reliability of technology is ultimately proven by where it enters. The five years of the SJ_SMOKE family show that the validation curve has entered an environment that has become increasingly harsh over time.

September 2021, Samsung SDI battery charger/discharger. Applied not only in Korea but also to multiple lines at the Hungarian factory. It is an environment where minute concentration changes, at which battery cells begin to emit gas due to thermal runaway, must be detected in real time to prevent them from escalating into accidents. The SJ_SMOKE_Vol, a 1~4V DAC output version, was applied, and its vibration robustness and continuous concentration output were decisive factors.

May 2022, Hyundai’s early double-decker hydrogen bus hydrogen tank. An environment where the risk of explosive fuel leakage and fire exists simultaneously and vibration is constant. It was the stage where the integrated structure of ADPD188BI demonstrated its vibration robustness.

February 2026, power plant distribution boards nationwide. It is a complex, harsh environment where condensation, dust, vibration, and electrical noise exist simultaneously, and requires central integrated monitoring of multiple measurement points. The SJ_SMOKE_RS485 was adopted for this application. The decisive factors were the ability to simultaneously measure and transmit precise smoke concentration, along with ±1.0℃ temperature and ±1.0%RH humidity, via RS-485 Modbus, and the capability for dual-wavelength identification to prevent mistaking condensation (water vapor) for smoke. Furthermore, it was equipped with details for survival in industrial environments, including a 1.3mm steel case, anti-corrosion paint, and an aluminum bug screen to prevent external insect intrusion.

These three cases are not merely a list of clients. The flow shows that the environmental difficulty level increased step by step—vibration (2021) → vibration + flammability (2022) → vibration + condensation + communication integration (2026)—and that the SJ_SMOKE family provided a solution each time.

From a single alarm device to an industrial IoT node

What the SJ_SMOKE_RS485 ultimately demonstrates is the digital transformation of fire safety. While conventional detectors were unidirectional alarm devices that sent only a single bit indicating "fire / no fire," semiconductor-based precision measuring instruments are closer to IoT nodes that transmit time-series data—such as concentration, temperature, and humidity—via industrial communications. This data serves as input for predictive maintenance, environmental trend analysis, and multi-point correlation analysis, extending beyond simple tripping. Bringing fire alarms, rendered ineffective by false alarms, back into the realm of trust cannot be achieved simply by replacing components. It requires the redesign of the optical structure, firmware algorithms, industrial communications integration, and verification for harsh environments to all go hand in hand. The SJ_SMOKE family, having passed through the most demanding positions in the industrial field for five years, is demonstrating that such integration work is possible even in the hands of a small but strong Korean company.