The thermometer in question must be compared to a thermometer traceable to the National Institute of Standards and Technology (NIST) at three or more temperatures levels, such as 32 ° F, 100 ° F a180 ° F, one of which should be the temperature range in which the thermometer is expected to be used. The thermometer must be within the limits shown in the previously referenced table at all points checked. A field inspection consists of visually checking the glass capillary for breakage and separation of the liquid column. A thermometer with a separated liquid column must not be used. If the column is 4.3.3 Immersion times Whenever any thermometer is used it must remain immersed n the liquid long enough to reach thermal equilibrium with the material being measured. With mercury in glass thermometers this is often longer than many of us realize. The following tables show the required immersion times: rejoined, it may be used provided that it successfully passes a bench inspection.
Liquid in Glass Thermometer Immersion Times
4.3.1 Accuracy Requirements The following table shows the accuracy requirements for the typical liquid in glass thermometers used in the petroleum industry.
Recommended immersion times (minutes) In motion stationary
Api gravity at 60 ° f
>50
5
10
40 to 49
5
15
30 to 39
12
25
20 to 29
20
45
<20
45
80
As seen from the above tables, immersion times for heavy products with low API's is considerable. From a practical point of view, liquid in glass thermometers are generally used only on light products.
4.4 Portable Electronics Thermometers The most important point to remember when using a "thermoprobe" is not directly related to temperature determination. Always ground your unit prior to opening the gauge hatch.
4.3.2 Accuracy Verification A bench inspection is required for every thermometer before it is first put into service and annually thereafter.
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