Maintenance 7-7
January 2006
Incorrect Dew Point
Display
If the dew/frost point reads incorrectly, first check the standard
preventive maintenance items:
1. Clean the mirror (see Cleaning the Sensor Mirror on page 7-1).
2. Balance the sensor optics (see Balancing the Sensor Optics on
page 7-2).
An alternative method for checking the accuracy of the unit’s
electronics is to use a precision resistance decade box in place of the
platinum thermometer. Wire the decade box to the unit’s sensor
connector as shown in Figure 25, and verify that the resistance
settings shown in the table produce the temperatures shown.
Figure 7-2: Using a Resistance Decade Box
0.0
–10.0
–60.0
°C (±0.1)
Display Reading
60.0
10.0
Din Type 100 Ohms at 0°C 0.385 Ohms/°C
Resistance Table
RX10
123.24
RX0.01
RX0.1
RX1
76.33
100.00
103.90
96.09
Resistance
Ohms
3
Resistance
Decade Box
RX100
LOWHIGH
14
4
15
140.0
–76.0
32.0
50.0
14.0
°F (±0.2)
Optica
Connector
Cable
Sensor
Optica
Connector
Cable
T
L
J
K
Sensor
D2
1123HK
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