Section 8. Operation
365
The reference junction temperature measurement can come from a PanelTemp()
instruction or from any other temperature measurement of the reference junction.
The standard and extended (-XT) operating ranges for the CR3000 are –25 to 50
°C and –40 to 85 °C, respectively. These ranges also apply to the reference
junction temperature measurement using PanelTemp().
Two sources of error arise when the reference temperature is out of the
polynomial-fit range. The most significant error is in the calculated compensation
voltage; however, a small error is also created by non-linearities in the Seebeck
coefficient.
Reference Temperature Compensation Range and Error
TC Type
Range °C
Limits of Error °C
1
T
–100 to 100
± 0.001
E
–150 to 206
± 0.005
J
–150 to 296
± 0.005
K
–50 to 100
± 0.01
1
Relative to ITS-90 Standard in NIST Monograph 175
Thermocouple Error Summary
Errors in the thermocouple- and reference-temperature linearizations are
extremely small, and error in the voltage measurement is negligible.
The magnitude of the errors discussed in Error Analysis
show that the
greatest sources of error in a thermocouple measurement are usually,
•
The typical (and industry accepted) manufacturing error of thermocouple
wire
•
The reference temperature
The table Thermocouple Error Examples
(p. 365)
tabulates the relative magnitude of
these errors. It shows a worst case example where,
•
A temperature of 45 °C is measured with a type-T thermocouple and all
errors are maximum and additive:
•
Reference temperature is 25 °C, but it is indicating 25.1 °C.
•
The terminal to which the thermocouple is connected is 0.05 °C cooler
than the reference thermistor (0.15 °C error).
Summary of Contents for CR3000 Micrologger
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