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7.2.1.10 Standard Thermocouple Conversions
Standard thermocouple conversions include types B, E, J, K, N, R, S, T, and
Au-Pt. Voltage is converted to temperature using standard reference functions.
(For additional information consult the publication NIST Monograph 175.)
You can specify internal or external reference junction compensation (RJC)
with the RJC parameter. (See Table 9 on page 129.) With internal RJC, the tem
-
perature of the thermocouple cold junction is measured automatically and used
to calculate the absolute temperature of the thermocouple. With external RJC, a
reference junction at a known fixed temperature is used and the value of this
fixed temperature reference must be entered in the RJT parameter and is used
to calculate the absolute temperature of the thermocouple.
Conversions for each of the thermocouple types accept functional calibration
data. This can be used to improve the measurement accuracy. The parameter,
Tn, is the temperature of the point in degrees Celsius. The parameter, ADJn, is
the temperature deviation from the reference function at the point in degrees
Celsius. The temperature measurement is adjusted by this amount when mea
-
suring at this temperature. A polynomial interpolation function is used for mea-
surements between calibration points. If calibration data is not available or is
not to be used, the ADJn parameters should all be set to 0.0. This causes the
temperature to be calculated according to the standard reference functions.
7.2.1.11 Thermocouple Polynomial Conversion
The thermocouple polynomial conversion allows calculation of temperature by
polynomial conversion.
When the Thermocouple Polynomial conversion type is selected, the coeffi-
cients are displayed on the right portion of the bottom of the display. Use the
UD buttons to scroll through the coefficients. Use the Enter buttontoedit
and save the new setting. Press and hold the Exit button to cancel to the main
display or press the EXIT button to cancel and to move to the next parameter.
On the last parameter, press the Exit button to exit to the menu.
The following equation is used for the thermocouple polynomial conversion:
tE C CE
i
i
i
([ ])[ ]mV °=
=
∑
0
6
The user-defined parameters for the thermocouple polynomial conversion are
the coefficients c
0
(C0) through c
6
(C6). The user can specify internal or exter
-
nal reference junction compensation (RJC; see Table 9 on page 129). If external
RJC is selected, the user enters the temperature of the RJC reference in the ref
-
erence junction temperature (RJT) parameter.
The output of the thermocouple, in millivolts, at 25°C with the reference junc
-
tion at 0°C, is mV (25°C). For example, for a type K thermocouple, mV(25°C)
is 1.0002.
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