Test accuracy and reliability:
Equipment for custody transfer applications need a certificate issued by a certified check as proof of his ability (in other words, competition and self-verification) and accuracy.
Examples of accredited authorities:
- PTB Physikalisch-Technische Bundesanstalt =
- NMi = Nederlands Meetinstituut
- NIST = National Institute of Standards and Technology
Protection software for custody transfer operations:
All equipment calibration parameters that may modify, falsify or delete daftxde measurement equipment Custody Transfer mode must be protected with passwords or access codes to prevent outside agents (ie a user) can change.
Hardware protection against unauthorized access to the measuring point:
The electronics compartment of the meter must be provided with a seal, like the connection compartment sensor remote version. The diagram of seals is part of the certification and documentation should be included in the operating instructions supplied with the equipment (Fig. below).
Figure: Diagram of a flow meter seals "Promag" E + H.
A = Precinct electronics compartment
Precinct B = Sensor connection compartment after installation (remote version)
The authority also sets a calibration seal the connection compartment of the transmitter with dual output boost.
Limits of error in legal control of weights and measures:
In measurement systems distinguish between "water" and liquid "other than water" for historical reasons. They have also understood the limits of error for water meters that are applied in Germany and some other countries in the EC, may seem curious to an outside observer. Mechanical water meters are divided according to "load ranges of values" with different error limits, and classes according to their rangeabi-ity, a peculiar, yet easy to assimilate:
- Class A: Accountants simple turndown Qmin / Qmax = 1:25
- Class B: more sophisticated mechanical counters turndown Qmin / Qmax = 1:67
However, the practical possibilities of these classifications to the state of the art electromagnetic water meters are more difficult to observe. The "load ranges of values" do not apply to devices of this upo and turndown 1:500 (within 2% error limit) are common. As a result, increasingly used in water supply networks.
Fig: Fields of flow values and error limits for custody transfer measurements in cold water. All limit values depend on the counter, the nominal size and class certification.
Qmin = minimum flow, Qt = Limit value range between the lower load and higher Qmax = Maximum flow, Qn = Nominal flow rate, equal to half of Qmax and is the parameter used to classify the counter.
- The limit of error in the lower load value (1) is ± 5%
- The limit of error in the field of higher load values (2) is ± 2% or ± 3% for hot water
Elastomers and Coatings
All elastomers and synthetic materials should be approved by the FDA or an equivalent entity. They should be resistant to cleaning processes in place (CIP) or sterilize in place (SIP). In general, boards are often used specially designed and molded. This will guarantee that there are cracks in places where they are in contact with the fluid for different field values of pressure and process temperature. Pay special attention to the following:
- The joint surfaces in direct contact with the product should be as small as possible,
- All together in direct contact with the fluid must be able to slough,
- A pre-load ensures that joints are free of cracks.
