OHAUS ST400M Portable Multiparameter Meter

Overview

The OHAUS ST400M Portable Multiparameter Meter is an engineered field-deployable electrochemical analyzer designed for reliable, high-fidelity measurement of pH, conductivity, salinity, resistivity, and temperature in uncontrolled environmental conditions. Built upon OHAUS’s legacy of metrological rigor—spanning over 110 years in precision instrumentation—the ST400M applies standardized potentiometric (pH), conductometric (conductivity/resistivity/salinity), and thermistor-based temperature sensing principles to deliver traceable, repeatable results across diverse aqueous matrices. Its architecture conforms to fundamental electrochemical measurement standards, including ISO 7888 (conductivity of water), ASTM D1125 (electrical conductivity of water), and USP (pH measurement). The instrument operates under ambient temperature ranges from 0 °C to 50 °C and is calibrated using NIST-traceable international buffer solutions (pH 4.01, 7.00, 10.01), ensuring alignment with global laboratory reference practices.

Key Features

• IP67-rated enclosure and matching IP67-certified electrodes—fully protected against dust ingress and immersion in water up to 1 m for 30 minutes—enabling robust operation in rain, splashing, mud, or marine splash zones.
• Integrated rechargeable lithium-ion battery delivering up to 40 hours of continuous measurement time per full charge; supports ≥300 charge cycles without significant capacity degradation.
• Backlit monochrome LCD with 128 × 64 pixel resolution displays real-time parameter values, electrode status (e.g., slope, offset, response time), calibration history, and battery level—all simultaneously and without menu nesting.
• Auto-ranging conductivity measurement (0.00 µS/cm to 200.0 mS/cm) with automatic temperature compensation (ATC) based on user-selectable algorithms (linear, NaCl, or natural water modes).
• Dedicated temperature sensor (NTC 30 kΩ) embedded in the combined pH/conductivity probe ensures synchronized thermal correction across all parameters.

Sample Compatibility & Compliance

The ST400M is validated for use with freshwater, wastewater, surface water, estuarine, and seawater samples—provided total suspended solids (TSS) remain below 500 mg/L and redox-active interferents (e.g., sulfides, hypochlorite >1 ppm) are absent or pre-treated. Electrode compatibility includes standard combination pH/conductivity probes with integrated temperature sensors (e.g., OHAUS EC-PC-1). All measurements comply with GLP documentation requirements: each stored record contains timestamp, parameter value, unit, electrode ID (if encoded), calibration date, operator ID (via optional alphanumeric input), and environmental temperature. Data integrity meets FDA 21 CFR Part 11 readiness when paired with OHAUS LabConnect™ software (v3.2+), supporting electronic signatures and audit trails.

Software & Data Management

Data export is performed via micro-USB interface to Windows/macOS systems using OHAUS Data Transfer Utility—a lightweight, installer-free application that maps ST400M memory registers to CSV or Excel-compatible formats. Each stored entry includes a unique sequential ID, UTC timestamp (synced on connection), raw mV/µS readings, compensated values, and calibration metadata. The onboard memory retains 1000 measurements in non-volatile flash; overflow triggers overwrite protection (FIFO), preserving the most recent dataset. No cloud dependency or subscription model is required—data sovereignty remains fully under user control.

Applications

• Field monitoring of municipal wastewater effluent compliance (e.g., EPA Method 150.1 for conductivity, Method 150.2 for pH).
• Rapid assessment of acid mine drainage (AMD) sites where low-pH (5,000 µS/cm) conditions demand stable electrode performance.
• Coastal and estuarine research requiring simultaneous salinity (calculated from conductivity and temperature) and pH tracking during tidal cycles.
• Educational field labs where ruggedness, intuitive interface, and battery longevity reduce logistical overhead during multi-day sampling campaigns.
• Pre-screening of industrial process water prior to lab-based ICP-MS or ion chromatography analysis.

FAQ

Does the ST400M support two-point or three-point pH calibration?
Yes—it supports up to three-point pH calibration using internationally recognized buffer standards (pH 4.01, 7.00, and 10.01) with automatic slope calculation and diagnostic feedback on electrode health.
Can conductivity measurements be compensated for temperature using non-linear models?
Yes—the instrument offers three ATC modes: linear (default), NaCl-specific (per ISO 7888), and natural water (based on empirical polynomial coefficients for river/lake water).
Is the USB interface used only for data export, or does it support firmware updates?
The micro-USB port supports both data transfer and secure firmware upgrades via signed binary packages distributed through OHAUS’s official technical support portal.
What is the recommended maintenance interval for the integrated pH/conductivity electrode?
OHAUS recommends daily rinsing with deionized water, weekly storage in 3 M KCl solution, and verification of slope (≥95%) and zero offset (±30 mV) before critical field deployments.
Does the ST400M meet any formal regulatory certification for field use in EU or North America?
The device carries CE marking per Directive 2014/30/EU (EMC) and 2011/65/EU (RoHS); it is not ATEX-certified but complies with IEC 61010-1:2010 for safety in portable electrical measurement equipment.