Just Prove It!
Recently Lontek was asked to engage a local calibration company to basically prove the total system accuracy(data logger + probe) of the Graphtec GL820 data logger when measuring temperature.
The temperature sensor to be used on Channels 2, 8, 14 & 19 was a BAND 5 (1/10th DIN) three/four wire PT100 probe supplied by a local Australian temperature probe manufacturer. Type T thermocouples were connected to Channels 1 and 20.
Four calibration points were required, 0, 20, 25, & 30 °C to meets the customers requirements.
Instrument and Sensor Accuracy
Graphtec claim the accuracy of the GL820 as ±1.0°C for a range of -200 °C to 850 °C for RTDs, while the customer's accuracy requirements were ±0.2°C. The Band 5 (1/10th DIN) PT100 sensor is claimed to be 0.03 °C to 0.05 °C for the target calibration range of 0-30 °C.
The GL820 has a typical accuracy for the Type T thermocouple of ±0.1 % of reading + 0.5 °C for a measurement range of -100 °C to 400 °C. The reference junction compensation accuracy is ±0.5 °C. The Type T thermocouple accuracy is claimed to be ±0.5 °C.
Calibration and Adjustment
Graphtec data loggers have a unique feature where they can be adjusted by qualified technical personnel to a known reference and then calibrated again to prove the calibration accuracy.
Here's a copy of the Graphtec GL820 Calibration Certificate. Note the before and after results on pages 2 and 3.