Fluke Calibration 9173 Metrology Well

Display Accuracy

Most dry-wells are calibrated by inserting a calibrated PRT and adjusting internal control sensors. However, this approach has limited value due to:

• Differences between the reference PRT and thermometers being tested
• Thermal gradients in the block
• Inadequate immersion from short blocks

Metrology Wells overcome these issues through:

• Minimized temperature gradients, loading effects, and hysteresis
• Calibration using traceable, accredited PRTs
• Proprietary electronics with repeatable accuracy, exceeding specs by more than 10x
• Display accuracy from ±0.1 °C (typical temps) to ±0.25 °C at 661 °C

An application note is available to better understand the associated uncertainties.

Optional: For improved accuracy, Metrology Wells can be ordered with built-in electronics for external PRT reading using ITS-90 characterizations.

Stability

Fluke heat sources are among the most stable in the world—and Metrology Wells improve upon this legacy:

• Models 9170 / 9171: Stability of ±0.005 °C over the full range
• Model 9173 (700 °C unit): Stability of ±0.03 °C

Only fluid baths or primary fixed-point devices offer better performance. This level of stability cannot be matched by the “off-the-shelf” controllers found in most dry-wells.

Axial Uniformity

According to EA-10/13 guidelines, dry-wells should have a 40 mm zone of maximum homogeneity. Metrology Wells go further with:

• Dual-zone control
• Increased well depth
• Homogeneous zones extending 60 mm (2.36 in)
• Vertical gradients ranging from ±0.02 °C at 0 °C to ±0.4 °C at 700 °C

Specifications for axial uniformity are published and guaranteed for each unit.

Radial Uniformity

Defined as the temperature difference between wells:

• Metrology Wells use a strict definition—largest difference between homogeneous zones of wells ≤6.4 mm (0.25 in) in diameter
• Models 9170 / 9171 (cold units): ±0.01 °C
• Models 9172 / 9173 (hot units): ±0.01 °C to ±0.04 °C at 700 °C

Poorly designed sources or use of large probes can lead to large variations; Metrology Wells prevent this.

Loading Effects

Loading is the temperature shift when all wells are filled versus when only one is. Metrology Wells minimize this through:

• Deep well design
• Dual-zone controls
• Cold units show minimal effects, as low as ±0.005 °C

Hysteresis

Thermal hysteresis arises mostly from internal control sensors rather than high-quality reference PRTs. It reflects the difference in measurements at the same set point approached from different directions.

• More pronounced near midpoints of temperature ranges
• Metrology Wells use better internal components
• Hysteresis effects range from 0.025 °C to 0.07 °C

Immersion Depth

Deep immersion is key to minimizing axial gradient and loading effects. Metrology Wells accommodate sensor-specific factors such as:

• Sensor location and size
• Probe mass and width
• Lead wire configuration

Well depths:

• Models 9171 / 9172 / 9173: 203 mm (8 in)
• Model 9170: 160 mm (6.3 in), enabling performance to –45 °C

User Interface and Software Features

Metrology Wells are simple and intuitive to use, featuring:

• Large LCD display
• Numeric keypad
• On-screen menus in English, French, or Chinese
• Real-time display of block temp, reference temp, cutout temp, stability, and ramp rate

Interfaces and Automation:

• RS-232 serial interface
• Compatible with Model 9930 Interface-it and xModel 9938 MET/TEMP II software
• Supports fully automated calibration of RTDs, thermocouples, and thermistors

Pre-programmed functions (no PC required):

• Up to 8 set points with ramp/soak
• Automated “switch test” to identify thermal switch dead-band
• Dedicated °C/°F switch button

Inserts and Portability

• Choose from six standard inserts supporting both metric and imperial probe diameters
• Units are compact and lightweight—easy to deploy in various environments

Model 9170 Summary

• Temperature range down to –45 °C (in normal conditions)
• Stability: ±0.005 °C
• Immersion depth: 160 mm (6.3 in)
• Axial uniformity: ±0.02 °C
• Radial uniformity: ±0.01 °C

Specifications: Fluke Calibration 9173 Metrology Well