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Thermocouple Basics
A.3
Measurement procedure
The temperature of a thermocouple junction is determined
by the following summarized procedure:
• Measure the reference voltage (E
• Calculate the reference temperature (T
• Determine the reference correction voltage (E
• Measure the thermocouple voltage (E
• Calculate the thermocouple correction voltage (E).
• Determine the thermocouple temperature (T).
The complete step-by-step procedure follows:
1. Read the voltage (E
) developed by the Model 2001-TC-
1
SCAN reference junction. Assuming a temperature co-
efficient of +200µV/°C, and an offset voltage of
+54.63mV at 0°C, convert the voltage reading to tem-
perature (T
) with the formula:
1
T
= (E
= 54.63mV) / 0.2mV per °C
1
1
T
represents the temperature of the Model 2001-TCS-
1
CAN isothermal connections.
2. Using the thermocouple lookup tables or the following
formula, convert the temperature (T
voltage. Use tables matching the type of thermocouple
connected to the Model 2001-TCSCAN. E
to the reference voltage that would result if an actual
thermocouple were used as a reference junction.
2
E
= a
+ a
T + a
T
+ a
r
0
1
2
3. Make a measurement of the voltage (E
the thermocouple connected to the Model 2001-TCS-
CAN.
4. Add the reference voltage derived in step 2 to the ther-
mocouple voltage measured in step 3.
E = E
+ E
r
t
A-2
).
1
).
1
).
r
).
t
) from step 1 to a
1
corresponds
r
3
4
T
+ a
T
3
4
) developed by
t
5. Convert the voltage sum (E) from step 4 to a temperature
(T) using either thermocouple lookup tables or the for-
mula:
T = a
+ a
E + a
E
2
+ a
0
1
2
The values for a
through a
0
couples are listed in tables located in Appendix B.
A.4
Measuring example
A measurement setup uses a Type J thermocouple. The volt-
age developed by the reference junction (channel 1) is
61.83mV. The voltage read from the thermocouple is
14476µV.
1. Find the temperature of the isothermal connections. The
voltage from the reference sensor is 61.83mV.
(61.83mV – 54.63mV) / 0.2mV per °C = 36°C
2. Using the appropriate formula or thermocouple lookup
tables (see Table 6.3.2 of NIST Monograph 125), find
the equivalent voltage developed by a Type J thermo-
couple at 36°C. This voltage is found to be 1849.1µV.
The formula shown in step 2 above would yield
1849.085µV.
3. The voltage developed by the thermocouple is measured
as 14476µV.
4. The sum of the voltage is 14476 + 1849.1, or
16325.1µV.
5. Using the appropriate formula or thermocouple lookup
tables (see Table A6.2.1 of NIST Monograph 125), find
the temperature for a Type J thermocouple correspond-
ing to 16325.1µV. This temperature is 300.0°C. The for-
mula shown in step 5 above would yield 299.995°C.
It is not necessary to make these calcula-
tions when using the Model 2001 Multim-
eter,
which
conversion automatically.
E
3
+ a
E
4
3
4
for the supported thermo-
4
NOTE
performs
temperature
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