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1010PVNFM-3A
Section 2
Return to the graph screen and observe the relative position of the up and down waveforms.
In a properly correlated receive signal the two images should be nearly superimposed on top
of each other, even during high flow conditions. In the unlikely situation where the two im-
ages appear to be offset by one or more receive cycles then the flow readings should be consid-
ered questionable.
Command Modes
Although the 1010 signal processing algorithms are capable of accommodating a very wide
range of signal conditions, it may be desirable to override these default settings under ex-
tremely difficult operating conditions. The following functions are available for this purpose:
Digital Damping Control: (Hot Key 1 and 2)
The System 1010 permits user modification of the digital averaging used by the signal pro-
cessing routines. In general, the default damping values selected by System 1010 will provide
optimal performance over a wide range of transit time applications. However, in extreme
cases of unstable flow profile, low signal levels or high aeration it may be necessary to over-
ride these default settings to permit uninterrupted and reliable flow measurement.
The 1010 Graph Screen includes the capability to access a set of command codes, which enable
a user to override a number of default setup parameters. The most important parameter is the
digital damping control
, which can be accessed by pressing number <1> or <2> on the keypad
while in the graph screen mode.
Pressing the <1> key will cause [MinDamp #] to appear on the command line at the lower left-
hand corner of the screen. The number listed to the right of the command code represents the
exponent in the System 1010 exponential averaging routine, where the larger the number the
greater the digital averaging. Pressing the <+> key will increase the damping value. Like-
wise, pressing the <-> key will decrease the damping value. To exit this mode, press the <0>
key on the keypad.
Pressing the <2> key will bring up the [MaxDamp] command. The function of this parameter
is similar to the [MinDamp] command described above, however, the two parameters interact
in the following manner. The MinDamp value must not exceed the MaxDamp value, therefore
increasing the MinDamp value above the previous MaxDamp value will set both parameters
to the same value. In most cases, it is preferred that both damping parameters be set to the
same value, however, in cases where rapid response to changes in liquid sound velocity is
required, the two values may be set differently. In this situation the meter will use the
MaxDamp value when sound velocity is stable, but then switch to a faster damping value
(limited by MinDamp) when a significant change in sound velocity is perceived. To exit this
mode, press the <0> key on the keypad.
Transit Time Adjustment: (Hot Key 3)
Observe the short vertical marker at the beginning of the receive signal in the Graph Screen
above. This line represents the position in time (Tn) where the 1010 flowmeter perceives the
arrival of the ultrasonic signal. There are actually two Tn markers, one for the upstream
arrival time and one for the downstream arrival time. For proper liquid sound velocity mea-
surement these Tn markers should be positioned near the beginning edge of the receive wave-
form envelope (as shown), however, in cases of poor signal conditions it is possible for this
measurement to be off by several receive waveform cycles. To adjust the Tn mark position
press the <3> key on the keypad to bring up the [TnSet] command.
