Wireless temperature data logger

Knowledge of temperature course during a certain time is needed in scientific, medical and industrial applications. In some applications, however, the recorded temperature course should be read wirelessly. This paper describes main principles applied in a set of mobile temperature data logger and portable reader/writer with wireless transfer of digitized temperature values. A mobile temperature data logger with RFID features was designed for applications, where portability and wireless data transfer is inevitable. Communicating reader/writer can be mounted on the wall or can be portable, too. Two main modes of operation during temperature data logging may be remotely chosen for a tag. Mode 1 - standard storing of data in preprogrammed regular acquisition time intervals (100 milliseconds up to 2 hours) with number of samples limited only by a data EEPROM memory size. Mode 2 - more memory size reducing method, when only breaking lower and upper temperature limits initiates storing the date and time stamp. However, the following date and time stamp is stored only when the temperature returns back into the temperature band between lower and upper temperature predefined limits. This mode 2 corresponds with a structure of data stored in data EEPROM memory. Enhanced mode can be set when the maximum or minimum temperature between breaking and returning points of a sampling temperature course is stored, too. This is a typical example for monitoring of food transport, where the time stamp and maximum temperature after breaking the limit are proofs to define the offender who damaged the transported goods.