Appendix | Radar Tank Gauge |
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11.4.3Custody transfer mode
7500 RTG is a weight and measure approved level transmitter. Either the innage or the ullage can be selected as the custody transfer variable.
The selected variable is the basis for the subsequent calculation of the current amount of product in a tank, along with other measured variables such as (average) temperature and pressure.
This opens up numerous application options in custody transfer:
•Quantity calculation of mineral oils
•Quantity calculation of alcohols
11.4.4Weight and measure approval, Standards Authorities ap- proval, Compulsory reapproval
The type approvals for custody transfer issued by the PTB and NMi, a copy of which is enclosed with every device, prove the fundamental suitability of the various types for custody transfer.
In addition to this, the accuracy of every single device is documented using a calibration certificate, which is issued in the factory after the device has been tested on a reference test rig.
On request, a separate initial verification of the devices can be carried out with a National Standards Authorities inspector present, who issues a preliminary test certifi- cate for every device. In the initial verification, the device is tested to ensure that it com- plies with the limit of error in legal metrology, which lies at
Essentially, this proves that the devices are weight and measure approved. The devices must not, however, be used in custody transfer mode straight away.
The measuring device is not approved until after the approval after installation by the Standards Authorities. For this, the device's level measurement is compared with the tank gauging by a National Standards Authorities inspector using manual dips (also "Ini- tial verification"). As a rule, a quiescent tank gauging is dipped by hand three times in a row and then compared with the value displayed by the level radar. Depending on national regulations, the transfer error limit, calculated as the arithmetic mean of the absolute deviations of all three measurements, must not exceed double the limit of error in legal metrology (compare, for example, the German "Eichordnung" or the American "API 3.1B", in which the necessary procedures are also defined).
Depending on national regulations, this test is repeated with various tank gaugings. Using linearization tables to compensate any
After the measurement has been approved by an inspector, he seals the level radar at the stamp position and thereby also secures the programming status of the device.
Those operating an approved level transmitter are obligated to obtain reapproval in accordance with the applicable national regulations from the Standards Authorities.
100 | Installation and Operations Manual |
