Temperature baths are instruments used to calibrate temperature sensors, switches and gauges. The temperature bath consists of a hot bath and a controller. The controller is used to set the temperature of the bath. 
The sensor or gauge to be calibrated is inserted in the bath and the temperature at which it is to be calibrated is set. Once the bath reaches the set temperature, the reading on the gauge is read. If it indicates the set temperature of the bath, the gauge is accurate. Sensors can also be similarly calibrated by comparing the bath temperature with the temperature indicated in the scanner or the PLC.
Temperature Baths are available as dry baths and wet baths. In dry bath, the sensor dimensions the size of the bath and the sensor perfectly fits the bath.
For sensors with irregular stem sizes, wet bath with a semi-solid paste which facilitates heat transfer is used.
Modern Temperature baths have accurate temperature controls and can produce reference temperatures with resolution of .1 degrees celsius.
They are also compact and portable.