Abstract: A mobile or transportable refrigerated container temperature monitoring system which includes digital monitoring and printout devices which provide accuracy and reliability, and means for periodically checking the monitoring means for operability and logging the results. An analog to digital converter is utilzed to convert analog temperature data obtained from thermistor sensors to digital form to provide digital data readout and to drive a digitally responsive printer. Sensing and control devices are provided to prevent printer jamming and compensate for widely varying temperature conditions. Automatically activated testing devices are provided which test and record the functionality of the thermistor temperature sensors by periodically applying a predetermined heat input to the thermistor temperature sensors and recording the responses including responses indicating errors, insuring reliability of the outputted recorded temperature data and pinpointing any improperly functioning sensors.