Instruction manual

Overview
2 Installation and Operations Manual
1.2 Custody Transfer Mode
The 7500 series 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
1.3 Weight and Measure Approval, Standards Authorities Approval, and
Compulsory Re-approval
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 certificate for every
device. In the initial verification, the device is tested to ensure that it complies with the limit of
error in legal metrology, which lies at ±2 mm for radar measuring devices in Germany.
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 installation and certification 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 “Initial 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 non-linearities that occur in measurement is permitted.
For this, the 7500 series RTG offers a special dip table, see Chapter 7.5 on page 55.
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 re-approval in accordance
with the applicable national regulations from the Standards Authorities.