Operating Manual

Accu-Wave Chapter 5 Radar Fine Tuning
TN Technologies 5-7
• “Do bypass range gate for near echoes” has been selected and the echo falls short
of the range gate
• “Do bypass range gate for far echoes” has been selected and the echo falls beyond
the range gate
• Past echoes have fallen outside of the range gate for a period equal to the “agitator
reject time” (range gate delay time)
If none of the above conditions are met, the next transmission is processed, a new echo
report is generated, and the entire process is repeated until one of the above conditions is
met. If no echo meets the above conditions for a specified period of time (the range gate
delay time), the echo is considered lost and the gauge will be in the “waiting for echo”
state. A second time parameter (time after echo loss before lost echo mode) defines the
time between the initial loss of the echo and when the gauge enters the lost echo mode, that
is, the range gate reverts to the not captured mode.
The optional selections to by-pass the range gate for near echoes, far echoes, or all echoes
are typically not required. The “by-pass near” selection can be used to provide a fast
response to rising level, while delaying response to echoes which appear to be beyond
(below) the material level. Similarly, the “by-pass far” selection can be used to provide a
fast response to decreasing level, while delaying response to echoes which appear to be
above the material level. This is one of several tools which may be used in combination to
reject multi-bounce echoes or echoes from the bottom of the tank as seen through a low
dielectric material.
Agitator Reject Time
The persistence (time) required to accept a new “true” echo, which falls outside the range
gate of the current true echo, is determined by the “Agitator reject time” (range gate delay)
entry.
As implied by its name, a primary purpose of the “agitator reject time” is to reject false
echoes due to an agitator that may have blades above the material surface or to delay loss
of echo. The reject time should be set to the time required for the blade to pass through the
microwave beam. The beam diameter increases by about one foot for each four foot
increase in distance from the top of the tank. For example, if the agitator blade is 20 feet
from the top of the tank, the beam can be considered to be about 5 feet wide. Based on this
beam width and the agitator speed, you can determine an appropriate entry for the agitator
reject time.
The range gate feature can also provide cleaner operation with agitated surfaces. In such
applications, momentary loss of the proper echo can cause the system to use a false echo
from some structure in the tank. Setting an agitator reject time of a few seconds will cause
the system to make many tries to get an echo close to the previous surface position before
accepting other echoes.
If a long agitator reject time is entered, the response of the system to fast changes in level
may be delayed. In some cases, this delay can be dealt with by selecting “Do” by-pass
range gate for far echoes. In this configuration, the system will perform range gate
processing on echoes which are closer to the measurement head than the measured level,