5520A
Operators Manual
4-74
8. Press REF SRC softkey until “external” is displayed.
9. Press the REF softkey to enter an external reference value.
10. Press 0 and E to set the external reference to 0 °C.
11. Press Pto go back one menu level.
12. Press O.
13. Allow the UUT reading to settle and then adjust the T1 offset adjustment (R7) for a
display reading of 25.2 °C ± 0.1 °C.
14. Change the calibrator output to 5380.7 °C. This places 53.807 mV on the tc
terminals.
15. Allow the UUT reading to settle and adjust R21 for a display reading of
+1370.0 °C ± 0.4°C.
16. Press Yon the calibrator to remove voltage from the UUT. Disconnect the UUT
from the 5520A. Power down the UUT by shorting the ON/OFF switch grid.
17. With an elastomeric switch pad in both hands, use the left one to short out the TP2
grid, and use the right one to first turn on the instrument and then quickly short out
the VIEW switch grid. Hold this position until the display is held in self-test. This
puts the UUT into the Reference Junction Sensor calibration mode, and the VIEW
maneuver turns off a filter so that the reading settled immediately.
18. Using a type K thermocouple bead (supplied with the 5500A/LEADS test lead kit)
and the 5520A Calibrator MEAS TC mode (press U), measure the reference
junction transistor temperature by placing the K-bead into the middle hole of the
isothermal block. The bead tip should be placed into the well, against the body of
Q1. Hint: Covering the well and positioning the bead with a piece of tissue may help
the bead stay in place. Do not hold the bead in place with your hands as this may
introduce a measurement error. Wait for the temperature reading to stabilize.
19. Adjust R16 for a temperature reading on the UUT that is the same as displayed on
the 5520A Calibrator.
Power down the UUT and reassemble.
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