Echo Detection with DATEM echo processing software
In real everyday level measurement applications, many echoes are returned from many different objects and there's no substitute for good transducer design which gets the best possible combination of signal strength and noise reduction to help follow the right echo. Firmware must also be able to distinguish between competing echoes and follow the right one - Pulsar's advanced Digital Adaptive Tracking of Echo Movement (DATEM) firmware is able to do this in the most demanding conditions. DATEM firmware is on both its ultrasonic and FMCW radar level measurement products.
Anatomy of an Echo Trace
- Echo Trace - Signal returned to the transducer mapping the application.
- Echo Marker - Echo that the software is analysing as the level to be measured.
- Gate - Set distance either side of the echo marker which is the 'normal' area that an echo will change within.
- Near Blanking - Distance from the transducer face in which no echo signal can be recorded.
- Far Blanking - Distance further than the measureement range of the transducer.
- Loss Limit - Threshold that indicates the echoes to be ignored because they are below this line.
- Datum line - Indicates the noise threshold calculated e.g. the base echo line.
- Empty level - The maximum distance that can be measured if the application (e.g. tank, wet well) was empty.
Echo Discrimination within the DATEM software
As shown in the opposite image, echoes over the loss limit line are considered and the echo from the 'pipework' is selected because it is large and nearest the transducer face. However, the correct level to measure should be the sewage level.
Using the DATEM software, specifically parameter 21, we can input the approximate distance to the sewage level (4m in this example). The controller then adjusts the blue 'loss limit' line around the unwanted echoes to mask them. Now the correct echo is selected and it is tracked as the level moves up and down. DATEM will also adapt to changing conditions such as the build-up of fat rings and debris. In most applications DATEM automatically finds the true level and locks on to it so you don't need to enter a distance in P21.
DATEM gives the 'highest value' to echoes within the 'gate' which allows the 'echo marker' to follow the selected echo as the level changes. For the 'echo marker' to jump outside of the gate, the new echo must be: 1) Above the loss limit; and 2) Persistent (this effectively deals with noise spikes and echoes from nearby transducers.)
Pulsar controllers and sensors are easy to use and provide an easy-driven menu that walks you through the set-up programme one parameter at a time. For an example of the simple process involved with setting the parameter 21 within DATEM, that teaches the system to lock onto the 'true level', please watch this video.