Campbell CR23X Spécifications télécharger pdf (Page 218)

SECTION 13. CR23X MEASUREMENTS

13-18

TABLE 13.4-2. Limits of Error on Datalogger

Thermocouple Output Linearization

(Relative to ITS-90 Standard in NIST

Monograph 175)

Limits of

TC Type Range °C

Error °C

T -200 to 87 ± 0.022

87 to 316 ± 0.042

316 to 400 ± 0.060

E -240 to -130 ± 0.40

-130 to 479 ± 0.05

479 to 1000 ± 0.21

K -56 to 413 ± 0.05

413 to 1372 ± 0.40

J -150 to 92 ± 0.02

92 to 412 ± 0.04

B 50 to 1007 ± 0.20

1007 to 1700 ± 0.50

R 0 to 579 ± 0.10

579 to 1450 ± 0.40

S 0 to 972 ± 0.17

972 to 1450 ± 0.40

N -200 to 1000 ± 0.0075

1000 to 1240 ± 0.01

REFERENCE JUNCTION COMPENSATION:

Temperature to Voltage

The polynomials used for reference junction

compensation (converting reference

temperature to equivalent TC output voltage) do

not cover the entire thermocouple range.

Substantial errors will result if the reference

junction temperature is outside of the

polynomial range. The ranges covered by

these polynomials include the CR23X

environmental operating range, so there is no

problem when the CR23X is used as the

reference junction. External reference junction

boxes, however, must also be within these

temperature ranges. Temperature difference

measurements made outside of the reference

temperature range should be made by obtaining

the actual temperatures referenced to a junction

within the reference temperature range and

subtracting. Table 13.4-3 gives the reference

temperature ranges covered and the limits of

error in the polynomials within these ranges.

Two sources of error arise when the reference

temperature is out of range. The most

significant error is in the calculated

compensation voltage; however, error is also

created in the temperature difference calculated

from the thermocouple output. For example,

suppose the reference temperature for a

measurement on a type T thermocouple is

300°C. The compensation voltage calculated

by the CR23X corresponds to a temperature of

272.6°C, a -27.4°C error. The type T

thermocouple with the measuring junction at

290°C and reference at 300°C would output -

578.7 µV; using the reference temperature of

272.6°C, the CR23X calculates a temperature

difference of -10.2°C, a -0.2°C error. The

temperature calculated by the CR23X would be

262.4°C, 27.6°C low.

TABLE 13.4-3. Reference Temperature

Compensation Range and Linearization

Error (Relative to ITS-90 Standard in NIST

Monograph 175)

Limits of

TC Type Range

°C Error °C

T -100 to 100 ± 0.025

E -150 to 206 ± 0.040

K -50 to 100 ± 0.030

J -150 to 296 ± 0.045

B25to80± 0.100

R -50 to 100 ± 0.020

S -50 to 100 ± 0.080

N -100 to 100 ± 0.001

ERROR SUMMARY

The magnitude of the errors described in the

previous sections illustrate that the greatest

sources of error in a thermocouple temperature

measurement are likely to be due to the limits of

error on the thermocouple wire and in the

reference temperature determined with the

built-in thermistor. Errors in the thermocouple

and reference temperature polynomials are

extremely small, and error in the voltage

measurement is negligible.

To illustrate the relative magnitude of these

errors in the environmental range, we will take a

worst case situation where all errors are

1 2 ... 213 214 215 216 217 218 219 220 221 222 223 ... 373 374

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