As the name implies, a dry-block calibrator has a metallic block that is heated or cooled and often includes an insert with pre-drilled holes of various diameters.  During calibration, the sensor being calibrated (called a device under test or DUT) is fully inserted into one of the pre-drilled holes.  Dry blocks work great for sensors such as dial thermometers, many RTDs, and thermocouples that are long, straight, and have a diameter that fits snuggly in the insert hole.

Some RTDs are short, have tri-clamp (tri-clover) fittings, or transmitter heads attached.  These short and odd-sized sensors can’t fit with proper immersion depth into dry blocks.  These types of sensors are best calibrated using PR551/PR553 Portable Calibration Baths