Operating Manual

Chapter 5 Radar Fine Tuning Accu-Wave
5-26 TN Technologies
Dynamic Threshold Setup
Note: The “Dynamic Threshold Setup” menu items are only displayed when the
“Service Only Items” are enabled. Direct Entry Code 025020.
If the dynamic threshold setup is required, the Agitator Reject Time (Direct
Entry Code 044003) should be increased to 8 seconds or longer.
Setting a dynamic threshold is intended to help track a turbulent process. When the surface
of the process material is turbulent or agitated, the amplitude of the echo from the process
material will fluctuate randomly. Setting a dynamic threshold will assist the gauge in
accepting a reliable (strong) return, while still providing a quick and reliable update of the
material surface level (or distance) measurement.
The amplitude of the previously accepted echo and two user-entered parameters are used
to dynamically set the minimum amplitude (signal strength) of the next acceptable echo.
The two parameters are:
• Dynamic Threshold Base - A constant (K), which is used to set the base value of
the dynamic threshold using the equation
dynamic threshold = amplitude of the last accepted echo/2
K
.
• Change Dynamic Threshold Factor - Each second that the gauge operates without
getting an acceptable echo, the dynamic threshold is multiplied by this factor.
These two parameters decrease the level of the dynamic threshold since the multiplication
factor is less than 1. After the gauge acquires an acceptable echo, the dynamic threshold
process starts over with the initial or baseline dynamic threshold value being set based on
the amplitude of the last accepted echo and the dynamic threshold base factor.
The rate at which the Dynamic Threshold changes can be smoothed by changing one or
both of the dynamic threshold smoothing factors. The “increase smoothing factor” (ISF) is
applied if the new base threshold value is greater than the old threshold. In this case the
dynamic threshold will be computed as:
threshold
old
+ [ISF x (threshold
new
– threshold
old
)].
The “decrease smoothing factor” (DSF) is applied if the new base threshold value is less
than the old threshold. In this case the dynamic threshold will be computed as:
threshold
old
+ [DSF x (threshold
new
– threshold
old
)].