KROHNE Summit 8800 Vol 2 - Manual (Page 35)

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08/2013 - MA SUMMIT 8800 Vol2 R02 en
SUMMIT 8800 METERING PRINCIPLES 03
3 .9 Run switching
Run switching (also known as meter run staging or tube switching) is a function that allows the
flow of fluid across multiple streams commonly used in stations and proving applications. The
main purpose of this function is to maximize the station accuracy by trying to maximize the flow
through individual meters without exceeding their maximum.
Meters have a limited flow range for which they work / work optimally. For minimum flow their
accuracy is limited, for maximum flow there can be a chance for overspeeding, damaging the
meter or limiting their accuracy. On the other hand stations have to deal with different flow
regimes, e.g. low flow during summer, high flow during winter.
The solution is to have multiple meters with the total capacity for high flow, while limiting the
number of meters used during low flow.
The run switch function in the SUMMIT is designed to do this automatically by switching valves
to activate or deactivate streams within a station thus optimising the number of meters used for
a certain flow.
3 .10 Proving
Proving is a function to determine and verify the accuracy of a stream flow meter. With proving,
the volume or mass flowing through a meter is compared with the same flow through the prover.
As the prover is considered to be correct it is also referred to as the ‘known traceable volume’.
The result of proving is the generation of a meter factor (MF) which is retro-applied to the flow
meter and which corrects the flow meter to give the same reading as the prover.
The SUMMIT 8800 flow computer can prove with the following prover systems:
• Unidirectional ball prover
• Bi-directional ball prover
• Piston small prover / compact prover
• Master meter
Historically provers are used in liquids while master meters are used for gasses. However now-
adays, due to the complexity of provers, master metering is starting to get inroads into liquids
too. In all cases, a prover / master meter is put in series with a meter under test to determine
the accuracy of the meter.
Provers are based on a pipe with in it a ball or piston, moving with the medium. Detector switch-
es are mounted at precise locations to detect the passing ball or piston. By very accurately
determining the volume between detectors, the amount of volume moved from the prover to
a meter can be determined and therefore the volume going through the meter. Since gas is com-
pressible, this system is only working for liquids.
Master meters are meters with a higher accuracy that the meters to be tested. They are put in
series with the meter under test. All the medium going through the master meter is also going
through the meter under test.
Conventional ball provers typically generate enough flow to get 10,000 or more meter pulses
from the meter under test to successfully complete a prove cycle. Small volume provers due
to size do not generate 10,000 pulses during a run cycle and are subject to pulse interpolation
(double chronometry). Both types of provers are available as bi-directional and unidirectional.