Hello,
Inside the USB-TC is a known millivolt reference. During calibration the channels are first connected to ground to measure offset. Then they are connected to the millivolt reference and with the two values, gain and offset coefficients are calculate and stored. This allows it to measure the thermcouple voltage accuractely.
During operation, it measures the thermcouple voltage, the CJC sensor and from these to values it determines temperature for the particular thermcouple type.
As for the calibration date, 11/26/15 is the last factory calibration date, which happens to be the manufactured data. I check, and this particular USB-TC has never been sent in for a factory calibration. One thing to keep in mind, the millivolt reference used in the self calibration does eventually drift. The factory calibration reset the reference so that future self calibration are accurate. The current price for a calibration is $62.75 plus shipping. Email your contact info and model/serial number to info@mccdaq.com to receive a quote.
Best regards,
John
