In-Process Temperature Mapping System for Industrial Freeze Dryers

This paper describes a low-invasive temperature mapping system specially designed for vacuum and nonaccessible environments, such as industrial freeze dryers. Thermal resistances tend to become quite hight in vacuum since convection is absent and even very small gaps have extremely conductive resistances. Temperature monitoring in the vacuum therefore requires sensors that do not inject power to minimize the self-heating and a special attention to the effect due to the involved thermal resistances. The proposed solution employs small autonomous measuring nodes that use a wireless connection to transmit the results and that are characterized to correct the thermal constant effect during temperature changes. The system has been designed for the monitoring of large freeze dryers, but its characteristics make it useful in many other vacuum conditions. The system is capable of monitoring the temperature of hundreds of points with an uncertainty of the order of a degree and with a cost per point of a few euros.