Dry block vs environmental chamber

A dry-block calibrator is a heated or cooled metal block with wells into which probes are inserted. An environmental (climatic) chamber is an enclosed volume of conditioned air, often with humidity control. Both can be used to calibrate temperature sensors; the right choice depends on the sensor, the range and the uncertainty you need.

Dry block

• Good for probe-type sensors that can be immersed to sufficient depth.
• Fast to reach and hold a set point; portable.
• Uncertainty is dominated by axial and radial gradients in the block, well fit, and immersion depth — small probes and short immersion suffer most.
• Not suitable for sensors that cannot be inserted, such as many data loggers with internal sensors.

Environmental chamber

• Suited to loggers, transmitters and assemblies that measure the air around them.
• Slower to stabilise; needs a reference thermometer placed close to the units under test.
• Uncertainty is dominated by spatial and temporal variation of the air inside the chamber, which must be characterised.
• Can add humidity as a controlled variable.

Choosing

Match the medium to how the sensor is used and to the uncertainty required. Calibrating a logger in a dry block would characterise a well the logger will never sit in. Calibrating a long-stem Pt100 in a chamber wastes the lower uncertainty a block or bath could give. In either case a traceable reference thermometer and a documented method are what make the result defensible.