YSI 550A Dissolved Oxygen Meter

Overview

The YSI 550A Dissolved Oxygen Meter is a field-deployable, rugged handheld instrument engineered for high-reliability dissolved oxygen (DO) and temperature measurements in diverse aquatic environments—including freshwater, seawater, and wastewater. It employs steady-state polarographic sensing technology, utilizing a Clark-type electrochemical cell with a replaceable PE membrane cap and internal electrolyte solution. This principle relies on the diffusion-controlled reduction of molecular oxygen at a polarized cathode, generating a current proportional to DO concentration. Temperature is concurrently measured via a precision thermistor embedded in the sensor tip, enabling real-time thermal compensation. The instrument’s extended measurement range (0–50 mg/L or 0–500% air saturation) supports both regulatory compliance monitoring and research-grade profiling across eutrophic, hypoxic, and supersaturated conditions. Its compact, IP67-rated housing ensures operational integrity during immersion, rain exposure, or accidental drops—critical for field technicians conducting routine water quality surveys under variable environmental conditions.

Key Features

• Rugged IP67-rated enclosure certified for dust-tight operation and submersion up to 1 meter for 30 minutes
• Field-replaceable dissolved oxygen probe (YSI 559) with user-serviceable membrane cap (YSI 5908 kit)
• Steady-state polarographic sensor with low-stirring-dependency PE membrane—reducing flow artifacts and improving measurement reproducibility in low-velocity or stagnant waters
• Simultaneous dual-parameter display: DO in mg/L and % air saturation, plus temperature in °C or °F (user-selectable)
• Integrated automatic compensation for temperature (–5 to +45 °C), salinity (0–70 ppt), and barometric pressure (via manual elevation input)
• High-contrast backlit LCD with large digits optimized for outdoor readability under direct sunlight or low-light conditions
• Button-initiated one-point calibration using air-saturated water or zero-oxygen solution—no external software required
• Extended battery life exceeding 2,000 hours at 25 °C using four AA alkaline cells
• Ergonomic handheld design with optional shoulder strap (YSI 5065) and protective carrying case (YSI 5060)

Sample Compatibility & Compliance

The YSI 550A is validated for use in natural surface waters, estuarine systems, wastewater treatment effluents, aquaculture ponds, and groundwater wells. Its robust construction and calibrated response meet field-testing requirements outlined in EPA Method 360.1 and ASTM D888–22 (Standard Test Methods for Dissolved Oxygen in Water). While not a GLP/GMP-certified system per se, its traceable calibration protocol, stable electrode performance, and audit-ready documentation support data integrity in environmental compliance reporting. CE marking confirms conformity with EU Electromagnetic Compatibility (2014/30/EU) and RoHS directives. All sensors and accessories comply with IEC 60529 for ingress protection and are compatible with standard USGS, ISO 5814:2012, and APHA 4500-O G methodologies.

Software & Data Management

The YSI 550A operates as a standalone field instrument with no onboard memory or USB connectivity—prioritizing simplicity, reliability, and minimal maintenance in remote deployments. All calibration parameters, units, and compensation settings are retained in non-volatile memory. For long-term data logging, users integrate the instrument with external field loggers or manually record readings into electronic lab notebooks (ELNs) compliant with 21 CFR Part 11 when used in regulated environments. Optional accessories—including cable lengths of 3.6 m, 7.5 m, 15 m, and 30 m—facilitate deployment from bridges, docks, or small vessels without requiring tethered data transmission. Documentation packages include calibration certificates traceable to NIST standards upon request.

Applications

• Regulatory monitoring of DO levels in rivers, lakes, and coastal zones per Clean Water Act Section 303(d) listing criteria
• Biochemical oxygen demand (BOD) incubation verification and wastewater treatment plant process control
• Aquatic ecosystem health assessment—including hypoxia mapping and seasonal stratification studies
• Environmental impact assessments (EIAs) for construction, dredging, or discharge permitting
• Academic and governmental limnological field campaigns requiring rapid, repeatable DO profiling
• Calibration verification of fixed-mount DO sensors in SCADA-based water quality networks

FAQ

What measurement principle does the YSI 550A employ?
It uses steady-state polarography with a Clark-type sensor, measuring oxygen reduction current at a gold cathode under constant polarization voltage.
Can the DO probe be replaced in the field without returning the instrument?
Yes—the YSI 559 probe is fully user-replaceable; membrane caps and electrolyte are serviced using the YSI 5908 kit.
Does the instrument compensate for salinity and altitude automatically?
Temperature compensation is fully automatic; salinity compensation (0–70 ppt) and barometric pressure adjustment (via elevation input) are supported but require manual entry.
Is the YSI 550A suitable for continuous submerged operation?
No—it is rated IP67 for temporary immersion only; prolonged submersion may compromise seal integrity and is not recommended for permanent deployment.
What is the warranty coverage?
Three years limited warranty on the meter body; one year on the dissolved oxygen sensor assembly, excluding consumables such as membranes and electrolyte.