Temperature calibrator 5901A-G

for temperature sensorsfor thermometersreference value

Key features

• Simple-to-use TPW cells with expanded uncertainty typically < ±0.0001 °C for main models.
• Available in multiple sizes and with glass or fused-silica (quartz) shells.
• Filled with ocean water of isotopic composition matching VSMOW.
• Provides a fundamental, reproducible temperature reference for calibration laboratories.

Product overview
5901 series water cells are evacuated and hermetically sealed after being filled with carefully distilled ocean water matching the Vienna Standard Mean Ocean Water (VSMOW) isotopic composition. Cells are produced to minimize contamination and preserve isotopic integrity over time.

Heavy water
Oxygen and hydrogen isotopes (including 17O, 18O and 2H) affect the TPW temperature. Ocean water is selected because its isotopic composition is among the heaviest typical values. Isotopic-induced TPW shifts can reach 0.00025 °C; the VSMOW-based cells have an uncertainty contribution below ±0.000007 °C (≈7 µK) for main models.

Isotopic verification options
Customers may request isotopic verification by laboratory analysis of a sampled portion or by receiving sealed ampoules containing water samples for independent testing.

Impurities
Impurities produce larger TPW errors than isotopic variations. Cells undergo multiple distillations and controlled manufacturing steps to maintain purity. Quartz cells can be filled directly from the distillation line to reduce contamination risk.

Glass vs. quartz
Borosilicate glass shells are cost-effective but exhibit greater long-term porosity; fused silica (quartz) is less porous and more stable. Typical drift for glass cells is on the order of 0.00006 °C per year.

Sizes and models
Models 5901A, 5901C and 5901D (glass or quartz) provide 265 mm immersion depth and differ mainly by probe-well inside diameter. Model 5901B-G is a smaller glass mini cell (for the 9210 Maintenance Apparatus) with shorter immersion depth. Bushings and adapters are available to fit various thermometer diameters.

Accessories
Accessories include the 2031A Quick Stick immersion freezer (dry ice/alcohol) to speed ice-mantle formation in larger cells, optional insurance services, and a selection of bushings and adapters for probe diameters.

Models (selection)

• 5901A-G — TPW Cell, 12 mm ID with handle, glass shell
• 5901A-Q — TPW Cell, 12 mm ID with handle, quartz shell
• 5901C-G — TPW Cell, 13.6 mm ID, glass shell
• 5901C-Q — TPW Cell, 14.4 mm ID, quartz shell
• 5901D-G / 5901D-Q — TPW Cell, 12 mm ID, glass or quartz shell
• 5901B-G — TPW Cell, mini, glass shell (for 9210 Maintenance Apparatus)
• Accessory bushings: 3901-11, 3901-12, 3901-13, 3901-21, 3901-22, 3901-23
• Accredited intercomparison: 1904-TPW

Notes
Various baths and maintenance systems are available to sustain the triple point for extended periods. Accredited test certificates can be provided under model 1904-TPW.

Technical specifications

• Expanded uncertainty (k=2): < 0.0001 °C for most 5901 models; < 0.0002 °C for the mini (5901B-G).
• Reproducibility: 0.00002 °C for main models; 0.00005 °C for the mini.
• Example dimensions: 5901A (50 mm OD, 12 mm ID, 450 mm length); 5901C (60 mm OD, 13.6 mm or 14.4 mm ID, 420 mm length); 5901B (30 mm OD, 8 mm ID, 180 mm length).
• Immersion depth (water surface to well bottom): 265 mm for 5901A/C/D; 118 mm for 5901B (mini).
• Shell materials: Borosilicate glass or fused silica (quartz).
• Water source: Ocean (VSMOW isotopic composition).
• dDVSMOW tolerance: ±10 ‰ (±1 %) for major models; ±20 ‰ for mini.
• Δ18O VSMOW tolerance: ±1.5 ‰ (±0.15 %) for major models; ±3 ‰ for mini.
• Effect of deviation from VSMOW on TPW: ≈ ±7 µK for major models; ≈ ±14 µK for mini.