Hello, how often should these temperature data loggers be calibrated?

The calibration for data loggers is a bit different than other devices as it’s more of a validation than an actual adjustment to bring it into range.

Because of this the calibration interval is really up to the end user as far as how often they want the device tested for accuracy.   Generally speaking temperature loggers stay relatively accurate for a very long time.

Accuracy for this device will vary  depending on the thermocouple sensor used.  In general, unless you are required to have a calibration certificate on file to meet a quality standard or regulation, it’s unlikely you need to purchase the calibration service as the device warranty states that the device will meet the specification for accuracy out of the box.