API MPMS 21.2:1998(R2011) pdf download.Manual of Petroleum Measurement Standards Chapter 21—Flow Measurement Using Electronic Metering Systems
6.1.4 To reduce system uncertainty, it is advisable to install and maintain on-line secondary equipment. For secondary device values that do not change appreciably (determined by agreement among interested parties), fixed or default second- ary inputs can be used and, for uncertainty calculation, maxi- mum expected deviations can be substituted directly for standard tolerances. It is important that fixed input values be revalidated periodically because, once set, they become easy to ignore.
6.1.5 For the purposes of uncertainty calculations, all sec- ondary input devices are considered to be maintained within the tolerances listed in Figure 2 from the sensor to the tertiary device (including any signal conditioning) specified in the standards listed in the figure. Any error as a result of deviation from zero is considered systematic for the quantity transac- tion period. The reader is referred to API MPMS Chapter 13.1 for the statistical background.
6.1.6 Different system configurations are possible. The cal- culations described here should be adaptable to many of them, but they are not representative of all possible system configurations. The diagram in Figure 2 describes a particular system configuration, and the results of example calculations using it are summarized in Table G-1 in Appendix G. These results are specific to the examples provided for natural gas liquid (NGL) and crude oil and include the components shown in Figure 2 but exclude the uncertainties of the pri- mary elements, the meters, and provers.
7.1.2 The meter in an ELM system either electrically or electro-mechanically produces pulses representing discrete units of volume passing through it. Methods for producing pulse outputs depend on the meter type. Electro-mechani- cally produced meter pulses are common to positive dis- placement and some turbine meters. Meters are also manufactured to provide both electro-mechanical and elec- trical outputs. The ELM system must be designed to accom- modate the characteristics of pulse outputs by allowing it to accurately detect the signal over all possible flow rates.
7.4.2 The ELM system shall include electrical transient suppression on all power, communication, and data inputs and outputs to provide protection from transient over-volt- ages. Transients appear on signal lines from a number of sources, including static discharge, inductive load switching, induced lightning, and coupled power lines. Transient sup- pressors are designed to either clamp and/or discharge the transient over-voltage, or to fail, thus shorting the over-volt- age to the ground. They are either of nonfaulting type that continue to operate many times or of the faulting type that require replacement following a substantial transient. A good earth ground is essential for the suppressor to operate prop- erly. Consult manufacturer for the proper type of suppressor to use.