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Resolving Calibration Problems
16116Maintenance.fm
Section 4
There is a significant time lag before the thermistor reaches the temperature
of its surroundings. Be certain the resistance reading is stable (not rising or
falling) when it is recorded.
4.2.5 Testing for Electrical Isolation
The probe’s thermistor and measurement components must be electrically
isolated. With an Ohmmeter, measure the resistance between pins A and D
and then pins B and C. An open circuit measurement (infinite resistance) is
expected. Any measurable resistance generally indicates leakage of
electrolyte under the probes cathode and will require probe body
replacement.
Figure 37
Probe Plug Conductors
4.3 Resolving Calibration Problems
In general, most calibration problems can be resolved by allowing enough
time for the probe’s thermistor and signal output to stabilize to their final
levels. This is particularly true when the probe is taken out of a cool sample
stream and placed into a warm beaker of deionized water and then is put back
into the sample stream. (See also all recommendations and guidelines in
Table 7 Thermistor Resistance by Temperature
Temp (°C)
Temp (°F)
Resistance ± 2% (k
Ω
)
0
32
316
5
41
248
10
50
195
15
59
155
20
68
124
25
77
100
30
86
81
35
95
66
40
104
54
45
113
44
50
122
37
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