6.1 SENSOR CIRCUIT BOARD
Inside the barrel of the Sensor probe, mounted directly at the tip, is the plug-in sensor
circuit board. This board has been calibrated at the Factory for a standard output level.
Since all boards have been calibrated for the same normalized level, they may be
replaced in the field without the requirement for recalibration, while maintaining the full
published system accuracy specification.
6.1.1 REPLACING THE SENSOR CIRCUIT BOARD
See Figure 6-1. For the HX85 and the HX86 series only, at the tip of the Sensor probe
is a snap-ring, or retaining ring (for the HX85A and HX86A series the filter cover is a
scew on cover). It must be removed in order to gain access to the Sensor board.
There is a groove at one end
of the ring. Using a very small
screwdriver or a small knife blade
inserted into the groove in the retaining
ring, lift it out of the machined groove
in the inside of the sensor shield
barrel. The ring can then be removed,
allowing access to the interior of the
Figure 6-1 Removing the Retaining Ring
6.1.2 REMOVING THE RETAINING COMPONENTS
Figure 6-2 shows the sequence of parts that must be removed in order to gain access to
the sensor board. All are easily removed once the retaining ring is out. Store them
carefully for re-installation later in the proper sequence.
The final item to be removed in the sequence is the plug-in sensor circuit board, which
can be seen through the slot in the sensor shield. There is a small hole near the tip of
the board to aid in removal. Inserting a small screwdriver in this hole and pulling
upward gently, unplug the board from the socket built into the probe.
Note: The small humidity sensor can be seen mounted near the tip of the board.
This is fragile. Take care not to break it during board removal or installation.