ProSoft Technology PTQ-AFC - Manual (Page 141)

PTQ-AFC ♦ Modicon Quantum Platform Meter Proving
Liquid and Gas Flow Computer for Hydrocarbon Products User Manual
ProSoft Technology, Inc. Page 141 of 259
June 23, 2011
Compact (short, small volume) Prover
A compact prover, or small volume prover (SVP), has a short barrel or tube with
a piston that travels the length of the tube. The piston has a valve that is opened
to allow it to return to its starting point without stopping the flow in the tube. Most
SVPs do not mount the switches to be tripped inside the tube. They mount the
switches externally on a bar that moves with the piston outside the tube and the
switches trip when they move past a fixed point. Each forth and back passage is
called a pass. SVPs can be much less expensive than LVPs, so they are often
preferred. Due to their small size they can collect at most a few hundred pulses
during a pass. The number of pulses in a single pass is a number too small for
calculating a meter factor with sufficient precision. The technique of double
chronometry is then used to determine a fractional pulse count of sufficient
precision. Even though a single pass in a SVP with double chronometry can yield
a pulse count similar in precision to that from a single run of a LVP, it is often the
practice to accumulate several passes into a single run so that the pulses
totalized for all passes of the run yield a number large enough for calculating the
required meter factor with sufficiently high precision.