Campbell Scientific CR1000KD CR1000 Measurement and Control System - Page 309

Section 8. Operation Error Calculations with Input Reversal = False µV error = gain term + offset term = (44500 µV * 0.12%) + (3 * 66.7 µV + 2.0 µV) = 53.4 µV + 200 µV = 7.25 µV (= 7.25 °C) 8.1.4.1.4 Ground Looping Error When the thermocouple measurement junction is in electrical contact with the object being measured (or has the possibility of making contact), a differential measurement should be made to avoid ground looping. 8.1.4.1.5 Noise Error The typical input noise on the ±2_5-mV range for a differential measurement with 16.67 ms integration and input reversal is 0.19 μV RMS. On a type-T thermocouple (approximately 40 μV/°C), this is 0.005°C. Note This is an RMS value; some individual readings will vary by greater than this. 8.1.4.1.6 Thermocouple Polynomial Error NIST Monograph 175 gives high-order polynomials for computing the output voltage of a given thermocouple type over a broad range of temperatures. To speed processing and accommodate the CR1000 math and storage capabilities, four separate 6th-order polynomials are used to convert from volts to temperature over the range covered by each thermocouple type. The table Limits of Error on CR1000 Thermocouple Polynomials (p. 309) gives error limits for the thermocouple polynomials. Table 66. Limits of Error on CR1000 Thermocouple Polynomials TC Type Range °C Limits of Error °C Relative to NIST Standards T -270 to 400 -270 to -200 -200 to -100 -100 to 100 +18 @ -270 ±0.08 ±0.001 100 to 400 ±0.015 J -150 to 760 ±0.008 -100 to 300 ±0.002 E -240 to 1000 -240 to -130 ±0.4 309