74X Series
Calibration Manual
24
Thermocouple Source
Proceed as follows to verify the Thermocouple Source function. This test uses a Type-K
thermocouple setting on the UUT.
1. Use Type-K thermocouple wire and copper wire to connect the HP3458A to the UUT
-TC jack as shown in Figure 11 (the HP3458A is used in place of the 5500A). The
type K-to-copper junctions should be either welded or made with tight screw
terminals and submersed in the lag bath (room temperature). Use the standard
thermometer (0.1% accuracy) to measure the temperature of the lag bath.
2. Set the UUT to the thermocouple source function, linear mode, TC type K; ITS-90
scale, internal reference, and °C.
3. Set the HP3458A to measure mV-DC.
4. Wait at least 1 minute for thermal "emfs" (caused by insertion of the connectors) to
dissipate, and allow the lag bath at least 15 minutes to stabilize.
5. Source each of the temperatures in Table 14 from the UUT. At each point, correct the
DMM measured voltage by adding the millivolt equivalent of the Type-K junction at
the lag bath temperature (use the Type-K ITS-90 chart).
6. Compare the result with the values under the appropriate column in Table 14.
7. When you are finished, press ctwice on the UUT to set the source function to off.
This saves battery life.
Table 14. Temperature Source Verification (Type-K Thermocouple, ITS-90)
UUT
Output
Nominal
DC mV
Minimum
1 Year
Maximum
1 Year
Minimum
2 Year
Maximum
2 Year
-180 °C -5.5504 -5.5616 -5.5390 -5.5653 -5.5353
0 °C 0.0000 -0.0197 0.0197 -0.0237 0.0237
800 °C 33.2754 33.2549 33.2959 33.2508 33.2999
1300 °C 52.4103 52.3928 52.4277 52.3893 52.4312
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