4.2.3
Setup
(Refer to Figure 4-1.)
1. To make a thermocouple transition junction, silver solder a piece of
copper wire to each (type K) thermocouple wire and insulate the
junction with a waterproof jacket.
2. Connect the thermocouple wires from the type K transition junction to
an OMEGA miniature thermocouple connector SMP-K-M.
3. Plug in the miniature connector to input TC1 of the Model 871A.
4. Connect the copper wires to the 100:1 divider (see Figure 4-1) with the
copper/wire (positive) junction connected through the 1.98 kilohm
resistor, to the dc calibrator positive terminal.
5. Prepare a distilled water ice bath as follows:
a. Drill a hole in the cap of a Dewar flask or Thermos
TM
to accommodate
the transition junction.
b. Firmly pack the flask with pea-size ice chips made from distilled
water and then fill the flask with distilled water.*
c. Replace the melted ice with more ice while removing excess water.
d. Place cap on the flask and insert the transition junction into the
flask. Allow 20 minutes for temperature stabilization.
*Using tap water may cause inaccuracies due to contaminants.
*The 20
Ω
resistor must be held at a uniform
temperature during calibration.
Figure 4-1. Calibration Setup for Model 871A
4.2.4
Calibration Procedure
It is not necessary to disassemble the case for calibration. All adjustments
are accessible by removing the covers shown in Figure 4-2.
1. Remove the battery and trimmer compartment covers from the Model 871A.
2. Turn the Model 871A on and perform the calibration adjustments listed
in Table 4-3.
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