ProSoft Technology MVI56-AFC - Manual (Page 45)

MVI56-AFC ♦ ControlLogix Platform Meter Proving
Liquid and Gas Flow Computer User Manual
ProSoft Technology, Inc. Page 45 of 316
February 25, 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.
Attention: While the MVI56-AFC module provides the capability to do small volume proving, an I/O
platform for ControlLogix that provides Double Chronometry pulse input signals does not exist at this
time. These pulse signals are needed for accuracy that is recommended per API standards. Use of this
module with small volume provers is not recommended as it may provide inaccurate results.