A temperature dry-block (or dry well) is a product that can heat and/or cool a metal block where suitable holes have been drilled for inserting temperature sensors. The holes need to be a tight fit to ensure proper temperature transfer. If the hole is too large, there will be air between the block and sensor, causing measurement error. The holes in the block are “dry”, so there is no liquid inside the holes. Typically, replaceable inserts are used in dry blocks for different kinds of sensors.
The benefits of a dry block include that they are typically portable (small and light), fast to use and they don’t get messy as no liquids are being used.
A temperature bath is a heat source that has liquid inside (water, oil, ethanol). The liquid is heated/cooled into the desired temperature and the sensors to be calibrated can be inserted into the liquid. The liquid is typically stirred for best homogeneity.
The befits of a bath is that you can insert different shapes of sensors into it, several at one time, and the homogeneity is very good. The drawback is that a bath is normally pretty large and heavy, temperature changes slowly and it may be messy to work with different liquids.