Campbell Scientific CR3000 Micrologger - Manual (Page 312)

Section 8. Operation
312
8.1.4.1.3 Thermocouple Voltage Measurement Error
Thermocouple outputs are extremely small — 10 to 70 µV per °C. Unless high
resolution input ranges are used when programming, the CR3000, accuracy and
sensitivity are compromised. Table Voltage Range for Maximum Thermocouple
Resolution
(p. 312)
lists high resolution ranges available for various thermocouple
types and temperature ranges. The following four example calculations of
thermocouple input error demonstrate how the selected input voltage range
impacts the accuracy of measurements. Figure Input Error Calculation
(p. 313)
shows from where various values are drawn to complete the calculations. See
Measurement Accuracy
(p. 284)
for more information on measurement accuracy and
accuracy calculations.
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.
Table 68. Voltage Range for Maximum Thermocouple Resolution
Reference temperature at 20°C
Thermocouple
Type and
Temperature
Range (°C)
Temperature
Range (°C)
for±20 mV
Input Range
Temperature
Range (°C)
for ±50 mV
Input Range
Temperature
Range (°C)
for ±200 mV
Input Range
T: -270 to 400 -270 to 395 not used not used
E: -270 to 1000 -270 to 300 -270 to 675 >675
K: -270 to 1372 -270 to 500 -270 to 1250 >1250
J: -210 to 1200 -210 to 385 -210 to 885 >885
B: -0 to 1820 0 to 1820 not used not used
R: -50 to 1768 -50 to 1690 -50 to 1768 not used
S: -50 to 1768 -50 to 1768 not used not used
N: -270 to 1300 -270 to 595 -270 to 1300 not used