The "thermoprobe" should be spot checked by comparing the ambient reading against a reference standard thermometer in a liquid or by use of a dry well device. If the readings differ by more than 0.25 ° C or 0.5 ° F the "thermoprobe" should be re- standardized before it is used for custody transfer. 4.4.3 Immersion Times One of the biggest advantages that a "thermoprobe" has over a liquid in glass thermometer is that the immersion time needed to reach thermal equilibrium is considerably shorter, as shown in the following table:
4.4.1 Accuracy Requirements The accuracy requirements for "thermoprobes" is dependent upon the operating range. When operating in a range of 0 ° F to 200 ° F the required accuracy is ± 0.2 ° F or ± 0.1 ° C. When operating above 200 ° F the required accuracy is ± 0.5 ° F or ± 0.25 ° C. 4.4.2 Accuracy Verification Before initial use and at least once a year thereafter, each "thermoprobe" shall be calibrated or re-standardized by comparing it at three or more temperatures with a thermometer traceable to the National Standard. The standardization check will ensure that the above referenced accuracy requirements are maintained. On a monthly schedule "thermoprobes" should be checked at two or more temperatures near the ends of its range against a traceable thermometer. If the above referenced accuracy requirements are not met, the device must be re-standardized. Additionally, the junction between the cable and probe should be checked for mechanical damage and the cable insulation should be checked for cuts, breaks or abrasion. In addition, a field verification must be performed before each use or once per day which ever is less frequent..
4.5 Temperature Readings In addition to making sure that your individual temperatures are correct, it is equally important to ensure that you take the required number of temperatures within the tank; because, in many tanks the temperature varies with the depth of liquid. While this is most common in heated fuel oils and heavy crudes it can also occur in light products. The minimum required number of temperature measurements are: A single middle of liquid temperature is required for: Tanks with 3m (10 feet) or less depth of liquid. Tanks with a capacity of less than 5000 barrels. Ship or barge tanks containing less than 5000 barrels of liquid cargo. Two temperature taken at the middle of the upper and lower halves are required for: Tanks with more than a 3m (10 feet) and up to 6m (20 feet) depth of liquid.
Portable Electronic Thermoprobe Immersion Times
Recommended in motion
Api gravity at 60 ° f
<20
75 seconds 45 seconds 30 seconds
20 to 39
≥40
The "thermoprobe" may be considered to have reached stability if, with a moving probe, the readout varies by no more than 0.1 ° C or 0.2 ° F for 30 seconds. Note: Motion consists of raising and lowering the probe 30 cm (1 foot) above and below the desired measurement depth.
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