Campbell CR3000 Micrologger, Руководство оператора

Страница: 364 / 644

Section 8. Operation
364
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 CR3000 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
CR3000 Thermocouple Polynomials
(p. 364)
gives error limits for the thermocouple
polynomials.
Limits of Error on CR3000 Thermocouple Polynomials
TC
Type Range °C
Limits of Error °C
Relative to NIST
Standards
T –270
to 400
–270 to –200 18 @ –270
–200 to –100 ±0.08
–100 to 100 ±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
–130 to 200 ±0.005
200 to 1000 ±0.02
K –50 to 1372
–50 to 950 ±0.01
950 to 1372 ±0.04
Reference Junction Error
Thermocouple instructions TCDiff() and TCSe() include the parameter TRef to
incorporate the reference junction temperature into the measurement. A reference
junction compensation voltage is computed from TRef as part of the
thermocouple instruction, based on the temperature difference between the
reference junction and 0 °C. The polynomials used to determine the reference
junction compensation voltage do not cover the entire thermocouple range, as
illustrated in tables Limits of Error on CR3000 Thermocouple Polynomials
(p. 364)
and Reference Temperature Compensation Range and Polynomial Error
(p. 365).
Substantial errors in the reference junction compensation voltage will result if the
reference junction temperature is outside of the polynomial-fit ranges given.