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5.3
PROBE COMPENSATION
The procedure outlined in the last paragraph provides accurate
absolute instrument calibration, but it cannot compensate for
probe inaccuracy. Probe errors near 32°F (0°C) can be minimized
by using the following procedure.
1. Make up an ice water bath by firmly packing a dewar flask
or Thermos with pea-size ice cubes made of distilled water
and then filling the container with distilled water. Replace
melted ice with new ice while removing excess water during
the calibration procedure.
2. Connect the probe to be compensated to the instrument.
3. Drill a hole in the flask or Thermos cap just large enough to
accommodate the probe. Place the cap on the bath
container and pass the probe through the hole until the
probe tip rests at the center of the ice water bath.
4. Allow 20 minutes for the test fixture temperature to stabilize.
With the model 868 on the 200°F range, adjust R104 for a
reading of 32.0 on the display. For the Model 869, R104
should be adjusted for a reading of 00.0 with the instrument
on the 200°C range.
NOTE
Using this method of probe calibration will uncalibrate the
instrument slightly when used with other probes.
5.4
TROUBLESHOOTING
The troubleshooting information, along with appropriate
schematics and parts lists, are included to serve as a guide to
enable equipment repair. The schematics and parts lists may vary
slightly from actual production units and are to be used as a guide
only. Likewise, the troubleshooting section is a guide only and
cannot cover all possible contingencies that may occur.
Each Model 868 and 869 is covered by a 13 month warranty as
described on the inside front cover of this manual. Warranty will
be void if the unit shows evidence of having been tampered with.
To gain access to the PC board for troubleshooting, the rear
cover and internal shield must be removed, as described in the
disassembly instructions. When troubleshooting or replacing
components, handle the PC board only by the edges to avoid
possible contamination.
Recommended Equipment: Digital Multimeter (DMM) with 10
megohm input resistance, ±0.05% basic accuracy; triggered
sweep oscilloscope with dc to 10 MHz bandwidth.
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