Dakota Ultrasonics PVX - Manual (Page 65)

PVX Precision Visual Thickness Gauge
61
7.6 Gates
The PVX is equipped with two gates that can be adjusted by the user to measure a
specific region or area on and between waveforms. In pulse - echo, only a single
gate can be used. The single gate has a threshold and a start point. In echo – echo
(interface-echo) mode, two gates are used. The same threshold level is associated
with both gates. The first gate has a starting point and threshold, and the second
gate has a start time that is determined by adding an adjustable HOLD OFF, or
delay, to the return echo measured by the first gate. These features are described in
more detail below:
Note: In order to adjust the gates they must be activated. The gates will only be
active if the measurement mode is set to P-E GT (pulse – echo w/gate1), or E-E
(echo – echo/interface-echo w/ gates 1&2). If the gates are not active, they will be
grayed out in the tabbed menus. Note: The setups contain the proper modes
according specific transducer types. The explanations that follow assume that the
proper measurement mode has been selected by selecting a specific setup. Refer to
page 27 for additional information on selecting a setup for the transducer being
used, which contains the correct measurement mode setting .
Gate 1
GATE 1 is used in both pulse-echo and echo-echo (interface-echo) modes. It has a
threshold and a start time. The purpose of GATE 1 is to prevent the PVX from
measuring unwanted surface noise in pulse-echo mode. This is accomplished by
changing the start time of GATE 1. It may be advantageous to activate a gate when
measuring aluminum, titanium, and stainless steel using lower frequency
transducers. However, if a high frequency transducer is being used, the gate may
not be necessary. Aluminum sometimes has an inherent surface noise problem that
can cause erroneous readings from the noise just following the initial pulse. By
blocking the surface noise with GATE 1 this error is eliminated. GATE 1 is also used
in echo - echo and interface-echo mode to force the PVX to measure between the
first and second back wall echoes or from the end of an interface (delay line), by
moving the start to the first back wall reflection of the test material.
The procedures to adjust Gate 1 are outlined below: