Leici SJG-203A Online Dissolved Oxygen Analyzer

Overview

The Leici SJG-203A Online Dissolved Oxygen Analyzer is a microprocessor-based electrochemical measurement system engineered for continuous, real-time monitoring of dissolved oxygen (DO) concentration and saturation in aqueous process streams. It employs a polarographic Clark-type membrane-covered amperometric sensor principle—where molecular oxygen diffuses through a gas-permeable membrane and undergoes reduction at a cathode surface, generating a current linearly proportional to the partial pressure of O₂. This analog signal is digitized, temperature-compensated, and converted into standardized units (mg/L and % saturation) using built-in calibration algorithms. Designed for integration into industrial water treatment infrastructure, the SJG-203A delivers stable, trace-level DO quantification across a broad operational temperature range—from cold intake water in municipal drinking water plants to high-temperature effluent streams in thermal power stations. Its architecture supports both bulk-phase monitoring (e.g., activated sludge aeration basins) and ultra-low-oxygen applications (e.g., boiler feedwater deaerator outlet control at sub-ppb levels when paired with appropriate low-range sensors).

Key Features

• Large dot-matrix LCD display showing simultaneous readouts of DO concentration (mg/L), DO saturation (%), and sample temperature (°C)
• Dual-point calibration capability: zero-oxygen (via sodium sulfite solution or nitrogen purge) and full-scale (air-saturated water or saturated air)
• Automatic temperature compensation (ATC) with user-selectable reference temperature; manual barometric pressure input for altitude correction
• Integrated data logging: stores up to 200 measurement records with configurable time-stamped intervals (1 min to 24 h)
• Programmable high/low limit alarms with relay output activation and visual/audio alert indicators
• Isolated 4–20 mA analog output with fully adjustable span (e.g., 0–10 mg/L mapped to 4–20 mA) and fault signaling capability
• RS-232 serial interface compliant with EIA/TIA-232 standard for direct connection to PLCs, SCADA systems, or local PCs
• IP65-rated polycarbonate enclosure suitable for indoor panel mounting or outdoor enclosures with environmental protection
• Non-volatile memory retains calibration coefficients, alarm thresholds, and configuration settings during power loss

Sample Compatibility & Compliance

The SJG-203A is validated for use in potable water, wastewater, aquaculture recirculation systems, cooling tower circuits, and steam-cycle condensate lines. It accommodates variable salinity (0.0–50.0 g/L NaCl equivalent) with automatic correction applied per ASTM D888–22 Annex A1 methodology. Sensor compatibility extends to standard 12-mm diameter galvanic or polarographic DO probes with BNC or DIN connectors. While the analyzer itself does not carry CE, UKCA, or UL certification out-of-the-box, its electrical isolation, creepage/clearance design, and fail-safe alarm logic align with IEC 61508 SIL 1 functional safety principles for non-critical process monitoring. For regulated environments (e.g., USP , EP 2.2.43), users must validate probe selection, calibration frequency, and data integrity protocols per site-specific SOPs and GLP/GMP documentation requirements.

Software & Data Management

Data retrieval occurs via ASCII command protocol over RS-232—supporting queries for live readings, logged entries, calibration history, and system diagnostics. No proprietary software is bundled; however, the device responds to industry-standard Modbus RTU commands (when configured via firmware update) for seamless integration into existing HMI platforms. All stored measurements include timestamp (YYYY-MM-DD HH:MM:SS), DO value, saturation %, temperature, and status flags (e.g., “CAL”, “ALARM”, “SENSOR_ERR”). Audit trail functionality is limited to manual log export; for 21 CFR Part 11 compliance, external historian servers or validated third-party SCADA systems must handle electronic signature, change control, and retention policies.

Applications

• Municipal water treatment: raw intake monitoring, ozonation chamber control, final disinfection verification
• Wastewater bioreactors: real-time aeration optimization in activated sludge and MBR systems to minimize energy consumption
• Aquaculture facilities: maintaining optimal DO thresholds (>5 mg/L) in hatcheries and raceways to support fish metabolism and reduce stress-related mortality
• Power generation: boiler feedwater deaerator outlet verification (with low-range sensor option) to prevent oxidative corrosion in economizers and turbine blades
• Environmental monitoring stations: long-term trend analysis of riverine DO dynamics correlated with BOD/COD loading and seasonal stratification
• Academic laboratories: teaching instrument principles of electrochemical sensing, mass transfer limitations, and Henry’s law behavior in aqueous systems

FAQ

What sensor types are compatible with the SJG-203A?

The analyzer accepts standard analog-output DO sensors with 0–20 mV or 0–100 mV polarographic output and integrated thermistor for temperature feedback. Both flow-through and immersion-style housings are supported.
Does the unit support automatic salinity compensation?

No—salinity compensation is manually entered by the operator prior to measurement. The device applies a fixed correction factor based on the input g/L value per ISO 5814:2012 guidelines.
Can the 4–20 mA output be assigned to temperature only?

Yes. Output mapping is fully configurable: users may assign the loop signal to DO concentration, saturation %, temperature, or a custom linear combination via setup menu.
Is firmware upgrade possible in the field?

Firmware updates require RS-232 connection to a Windows PC running Leici’s official configuration utility (v2.1+), which enables Modbus RTU mode and extended logging options.
What is the recommended calibration frequency for continuous operation?

Daily zero calibration is advised for critical applications (e.g., boiler feedwater); weekly two-point calibration suffices for municipal wastewater where DO variability is moderate and process stability is high.