Flow-X─ Function Reference
5-321
Flow-X IO Functions - fxDoubleChronometry
fxDoubleChronometry
The function provides double chronometry measurement for meter proving and calibration purposes
with a resolution of 100 nanoseconds.
The function monitors a (dual) pulse input signal provided by the meter under test and by one or more
digital signals that represent the start and stop of the measurement.
The digital inputs used for start and stop of the measurement are typically connected to the sphere
detector switches of a pipe prover or the piston detectors of a compact prover.
The start / stop signal may also be any other type of signal, e.g. a digital output from another flow
computer. This allows for flexible master meter configurations in which a single prove measurement is
performed by two separate flow computers, one that monitors the meter under test and one that
monitors the reference or master meter.
By using multiple Double Chronometry functions multiple prove measurements can be performed at
the same time by one and the same flow module.
Some examples of simultaneous prove measurements are:
For a prover with 2 begin and 2 end detector switches the flow meter can be proved against
all 4 the calibrated prover volumes at the same time.
With 2 detectors at one end of the prover (A and B) and 2 at the other end (C and D) there
are 4 possible detector combinations A-C, A-D, B-C and B-D, resulting in four available
prover volumes. By defining 4 Prove measurement functions all 4 prove volumes can be
used to prove the meter by a single prove sequence. The operator selects the primary
detector combination that will be used for calculating the new K factor or meter factor. The
result of the 4 detector combinations are compared to each other and an alarm is raised in
case of discrepancy.
Meters that operate in series can all be proved at the same time.
For meters that provide more than flow signal all signals can be proved at the same time
For provers with a range of calibrated prover volumes to accommodate proving of meters of
different capacities, multiple prover volumes can be processed at the same time.
Combinations of these scenarios are possible as well.
The double chronometry method comprises the measurement of the time between the start and stop
signals and the time between the two meter pulses that immediately follow the start and stop signals.
The flow module then determines the interpolated number of meter pulses that correspond to the
measurement start and stop signals as follows:
B
time
A
time
pulses
whole
count
pulse
ed
Interpolat
Time A between start and stop signal
Start
signal
detector
Stop
signal
Time B between the meter pulses following start and stop signal
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