Specifications

Section 4. Sensor Support
4-26
0.0012 * 52 mV = 62 µV or 1.78
o
C (62 / 34.9). The basic resolution on the
250 mV range is 66.7 µV or 1.91
o
C. Thus, the possible error due to the
voltage measurement is 4.38
o
C when reversing differential inputs, or 7.28
o
C
when not reversing differential inputs.
TABLE 4.4-2. Voltage Range for Maximum Thermocouple Resolution
(with reference temperature at 20
o
C)
TC Type and
temp. range
o
C
Temp. range
for ±2.5 mV
range
Temp. range
for ±7.5 mV
range
Temp. range
for ±25 mV
range
Temp. range for
±250 mV range
T -270 to 400 -45 to 75 -270 to 180 -270 to 400 not used
E -270 to 1000 -20 to 60 -120 to 130 -270 to 365 >365
K -270 to 1372 -40 to 80 -270 to 200 -270 to 620 >620
J -210 to 1200 -25 to 65 -145 to 155 -210 to 475 >475
B 0 to 1820 0 to 710 0 to 1265 0 to 1820 not used
R -50 to 1768 -50 to 320 -50 to 770 -50 to 1768 not used
S -50 to 1768 -50 to 330 -50 to 820 -50 to 1768 not used
N -270 to 1300 -80 to 105 -270 to 260 -270 to 725 >725
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.
4.4.1.4 Noise on Voltage Measurement
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 that this is an
RMS value; some individual readings will vary by greater than this.
4.4.1.5 Thermocouple Polynomial: Voltage to Temperature
NIST Monograph 175 gives high order polynomials for computing the output
voltage of a given thermocouple type over a broad range of temperatures. In
order to speed processing and accommodate the CR1000's 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. TABLE
4.
4-3 gives error limits for the thermocouple polynomials.