Sanxin SX751 Portable Multi-Parameter Water Quality Meter (pH/ORP/DO/Conductivity)

Overview

The Sanxin SX751 Portable Multi-Parameter Water Quality Meter is an engineered field- and lab-grade electrochemical analyzer designed for simultaneous, real-time measurement of pH, oxidation-reduction potential (ORP), dissolved oxygen (DO), conductivity, total dissolved solids (TDS), salinity, resistivity, and temperature. Built upon a modular potentiometric and amperometric sensing architecture, the SX751 integrates a high-impedance pH electrode interface (≥1 × 10¹² Ω input impedance), a polarographic DO sensor with built-in temperature and salinity compensation, and a four-range conductivity cell supporting electrode constants of 0.1, 1.0, and 10 cm⁻¹. Its measurement principles conform to established electrochemical standards: pH via Nernstian potential response, ORP via reversible redox couple detection, DO via Clark-type diffusion-limited current quantification, and conductivity via AC conductance at 1 kHz. The instrument operates across broad environmental conditions (5–35°C ambient, ≤85% RH) and meets IP57 ingress protection for dust resistance and temporary immersion—making it suitable for routine QC in municipal water labs, environmental monitoring stations, aquaculture facilities, and educational laboratories requiring traceable, multi-analyte data acquisition.

Key Features

• Simultaneous five-parameter display (pH, ORP, DO, conductivity, temperature) on a high-contrast LCD with backlight for low-light operation
• Auto-ranging conductivity engine covering 0.01 μS/cm to 100 mS/cm with selectable temperature reference (18°C, 20°C, or 25°C) and linear/non-linear compensation algorithms
• Polarographic DO sensor with automatic air-saturation and water-saturation calibration routines; supports manual barometric pressure input (66–200 kPa) and automatic salinity compensation (0–45 ppt)
• High-stability pH circuitry featuring ≤2 × 10⁻¹² A input current and ±0.01 pH meter accuracy over 3-hour stability test per ISO 5725-2
• Integrated data logging: 400 memory slots storing measurement ID, value, unit, temperature, and timestamp—exportable via optional IR interface or manual transcription
• Robust mechanical design: lightweight (180 g) pen-form factor with sealed electronics, rubberized grip, and IP57-rated enclosure compliant with IEC 60529

Sample Compatibility & Compliance

The SX751 is validated for aqueous samples across potable water, wastewater effluents, surface runoff, hydroponic nutrient solutions, and marine brines. Its electrode configurations support standard BNC pH/ORP connectors and 3.5-mm DO/conductivity jacks compatible with industry-standard Sanxin and universal replacement probes (e.g., PHB-1, DO-50, COND-1). All measurements adhere to fundamental metrological traceability requirements outlined in ISO/IEC 17025:2017 for testing laboratories. While not FDA 21 CFR Part 11–certified out-of-the-box, audit-ready documentation—including calibration logs, probe certification records, and instrument verification reports—can be maintained manually to satisfy GLP and basic GMP documentation expectations. The device carries CE marking per Directive 2014/30/EU (EMC) and 2014/35/EU (LVD), and complies with China’s CMC mandatory metrological verification requirements.

Software & Data Management

The SX751 operates as a standalone, firmware-controlled instrument without proprietary PC software dependency. All configuration—including calibration point selection (1–3 point pH, 1-point ORP, air/water DO, 1–2 point conductivity), temperature coefficient settings (α = 0.019–0.025 /°C), and unit toggling (mg/L vs. ppm, mS/cm vs. μS/cm)—is performed directly via intuitive membrane keypad navigation. Logged data are stored in non-volatile memory with automatic time stamping (real-time clock powered by backup capacitor). For regulatory environments requiring electronic record integrity, users may implement external validation protocols: printed calibration certificates, handwritten logbooks cross-referenced to instrument IDs, and periodic performance verifications using NIST-traceable buffer standards (e.g., pH 4.01, 7.00, 10.01; conductivity KCl 1413 μS/cm). No cloud connectivity or remote diagnostics are embedded—ensuring data sovereignty and minimizing cybersecurity exposure surfaces.

Applications

• Drinking water quality verification per WHO Guidelines and EPA Method 150.1 (pH, DO, conductivity)
• Wastewater treatment plant process control: aeration basin DO profiling, influent/effluent conductivity trending, and disinfection potential monitoring via ORP
• Aquaculture system management: daily DO and pH stability assessment in recirculating tanks and hatcheries
• Environmental field surveys: stream/river conductivity mapping for salinity intrusion detection and acid mine drainage screening
• Academic teaching labs: hands-on electrochemical fundamentals instruction including Nernst equation validation, oxygen solubility modeling, and Kohlrausch’s law demonstrations
• Pharmaceutical cleanroom water system spot-checks (PW, WFI) where rapid multi-parameter screening supplements fixed online analyzers

FAQ

What calibration standards are required for full functionality?
Standard buffers: pH 4.01, 7.00, and 10.01 (traceable to NIST SRM); ORP: Zobell’s solution (225 mV) or quinhydrone (+470 mV); DO: saturated air (calculated % saturation per temperature/barometric pressure) and saturated water (0% O₂ via sodium sulfite); Conductivity: KCl 1413 μS/cm (25°C) and/or 12.88 mS/cm.
Is the instrument suitable for seawater measurements?
Yes—its salinity range (0.01–100‰) and automatic 0–45 ppt salinity compensation enable reliable DO and conductivity readings in estuarine and coastal waters. For optimal accuracy above 35‰, verify electrode polarization stability during extended immersion.
How often should the DO membrane be replaced?
Under typical use (≤2 hrs/day), replace the polarographic membrane and electrolyte every 2–3 months; more frequent replacement is recommended in high-sediment or high-organic-content samples.
Does the SX751 support GLP-compliant audit trails?
It does not generate automated electronic audit trails. However, its 400-entry memory, combined with manual calibration logs and timestamped records, provides foundational traceability sufficient for internal QA and ISO 9001 audits when documented per site-specific SOPs.
Can conductivity measurements be converted to TDS using user-defined factors?
Yes—the meter allows manual entry of TDS conversion factors (0.4–1.0) depending on ionic composition, enabling customization for specific water matrices such as reverse osmosis permeate or industrial process streams.