pH Sensor 
SBE 18

The SBE 18 pH Sensor uses a pressure-balanced glass-electrode /Ag/AgCl-reference pH probe to provide in-situ measurements at depths up to 1200 meters (3900 ft). The replaceable pH probe is permanently sealed and is supplied with a soaker bottle attachment that prevents the reference electrode from drying out during storage. The sensor and associated interface electronics is a modular, self-contained package that is easy to install, service, and calibrate.

The SBE 18 is intended for use as an add-on auxiliary sensor for profiling CTDs (SBE 9plus; SBE 19, 19plus, and 19plus V2 SEACAT; and SBE 25 SEALOGGER). Power / signal interface cables and mounting hardware are available separately.

The SBE 18's interface circuits buffer and offset the differential glass-electrode/reference potential to produce a high-level pH-dependent output voltage. Computation of pH in engineering units is typically done using our SEASOFT^© V2 software.

Sea-Bird calibrates the pH sensor against precision buffer solutions (4, 7, and 10 pH ± 0.02 pH). These calibration results are tabulated on a certificate furnished with each sensor.

SPECIFICATIONS

pH

Measurement Range: 0 - 14 pH

Accuracy¹: 0.1 pH

Time Response²: 1 second

¹Stated accuracy is achievable with frequent field calibrations.
²Time to reach 63% of final value following a step change in pH.

Electrical/Mechanical

Power required: 6 - 24 VDC, 7 mA

Signal output: 0 to +5 V

Materials: Anodized aluminum (6061-T6) and stainless steel

Operating depth: 1200 meters (3900 ft)

Weight: 0.7 kg (1.5 lbs) in air, 0.4 kg (0.8 lbs) in water

ADDITIONAL INFORMATION / LINKS:

Documentation -- manual, photos, technical papers, application notes, etc.

• Print version of this specification sheet / brochure
• Application Notes:
  - 18-1: SBE 18, 27, and 30 and AMT pH Sensor Calibration
  - 18-2: SBE 18 pH Sensor Storage, Maintenance, and Calibration
  - 18-3: SBE 18 pH Sensor Hook-Up Instructions
  - 18-4: SBE 18 pH Sensor Calibration Equation Error
  - 71: Desiccant Use and Regeneration (drying)
  - 76: pH or pH/ORP Sensors and Moored Applications

Sales Information -- options, accessories, cables, mount kits, spares, etc.

• Configuration options & accessories:
  - Details for SBE 18
  - Listing for all products
• Cables
• Mount kits
• Spare parts

Links to Other Instruments of Interest

• CTDs that accept SBE 18 integration:
  - SBE 9plus -- premium CTD
  - SBE 25 -- CTD
  - SBE 19plus V2 -- small, economical CTD

Note: SBE 18 must always be mounted with the pH probe in a vertical orientation, as shown above. A right angle probe configuration is typically required for applications where the CTD is mounted horizontally (for example, in an extension stand below an SBE 32 Carousel Water sampler), and the SBE 18 is mounted to the CTD.