ABB LWT300 series, User Manual

Page: 55 / 108

Configuring the instrument
51
All these conditions are disabled by default. They are all enabled in a similar fashion, as explained
below:
1
Select
Device Setup
>
Application Setup
>
Process Condition
.
2
Highlight the relevant process condition and press
Edit
.
3 Highlight Enable and press OK .
Setting data filtering parameters
Processes can induce noise in level measurements. The LWT filtering feature is designed stabilize
measurements by filtering out extraneous data that could negatively impact the resolution of the
measured level (spikes, obstructions by mixer blades, lack of signal, etc.).
These parameters are set in the Filtering menu under the Device Setup menu.
—
Figure 38
The Device Setup menu
The various filters available are applied in a sequence as follows:
Damping — Median filter — Max Level Rate — Amplitude Threshold
Selecting maximum level rate
The maximum level rate is the rate at which the process will reach its Full limit. This influences the
processing speed of the instrument. The default value is
No Filter
.
To set the maximum level rate:
1
Select
Device Setup
>
Filtering
>
Max Level Rate
.
2
Press
Edit
.
3 Highlight the appropriate maximum level rate and press OK .
Setting up a median filter
The median filter is designed to filter out noisy measurement spikes in applications with fast transients
(e.g., rapidly varying processes, positioning applications, etc). It is used for discarding occasional false
measurements resulting from any occasional unwanted phenomena that might occur in the process.
The value entered corresponds to the number of measurements kept in the buffer. The filter then
generates and returns a median value of all the measurements kept in the buffer. The buffer size can
range from 1 to 50 measurements. The default value is
1
.
NOTICE
Selecting 1 measurement effectively disables the median filter as no averaging can be
performed.