HyQuest Solutions Pty Ltd
Point Velocity Display - Model PVD100
©
Copyright
4
Issue 1.00 4 Apr, 2007
2. Product Overview
2.1 Overview
The
PVD100
can measure and display velocity. Velocity can be either displayed in
meters/sec (m/sec) or feet/second (ft/sec) and is chosen by the user in a menu. When a
measurement is being made, the
PVD100
counts contact closures, measures elapse time, and
computes velocity to a precision of 0.001 m/sec or 0.01 ft/sec. The velocity is computed
based on a selection of a meter rating again chosen from a menu. During a measurement, the
PVD100
sends through the serial port the number of accumulating meter contact closures and
elapsed time at 1-second intervals. At the end of the measuring period, typically set for 40
seconds, a final count of the total number of contact closures and total measurement time is
transmitted. From this data, a connected hand-held computer with an appropriate applications
program can compute velocity for a discharge computation.
One of the most important operating features of the
PVD100
is the ability to signal process
each contact closure. Contact closures from any type of meter are inherently noisy causing
miscounting or double counting. The
PVD100
samples the input signal from the connected
meter and examines the signal to determine if a contact closure has occurred and if successive
signals are of the same characteristics. The
PVD100
then determines contact closure
conditions and either counts the signal closure or eliminates the condition as a noise pulse and
does not count the signal. For cat whisker contacts, this becomes extremely important since
cat whisker contacts offer the poorest quality for marking and counting rotations.
The
PVD100
offers (2) modes of operation, i.e. NORMAL and SLOW speed mode.
NORMAL is selected for meter rotations >0.076 m/sec while SLOW mode is for velocities
below 0.076 m/sec. To improve noise rejection, the sample rate of the input signal at the
SLOW speed mode (lower velocities) is 1/10 of the sampling rate that occurs during
NORMAL mode. This slower sampling rate improves performance for back rotations and
corroded whisker contacts at extremely low meter cup rotations. It is important to know that
the
PVD100
offers operational overlap at this 0.076 m/sec velocity selection in either mode
and therefore it is not necessary for the operator to know precisely the velocity of water for
selecting either mode.
Another important feature of the
PVD100
is the ability to detect faulty connections from the
meter through the wading rod to the connected
PVD100
. During power up of the
PVD100
, a
calibration of the input signal is performed. If a connection short is detected or other
condition such as faulty input electronics, the
PVD100
signals the operator of the condition
(by flashing the COUNT indicator) until the faulty condition is removed. Open circuit fault
conditions are observed simply as a failure to detect a contact closure. A very important
feature of the
PVD100
is the ability to detect a signal short during a measurement. If such a
condition is detected, the ‘*’ symbol is displayed until the fault condition is removed.
Importantly is the appearance of the ‘*’ symbol after the measurement to show the operator
that a fault condition occurred during the measurement and that the measurement should be
repeated. The measurement data that is transmitted through the serial port is also flagged to
indicate a faulty measurement.
