Time Base Filter

The Time Base Filter node processes an analog value received from the Input connector by applying a configurable computation method to a set of samples before sending the result to the Output connector.
The node can operate on a fixed number of samples or, when the Running window property is enabled, on the samples received within a moving time window.

This makes it possible to smooth analog values, calculate minimum or maximum values over time, and reduce the influence of short fluctuations in the input signal.

The Time Base Filter collects analog values from the Input connector and processes them according to the selected Computation method.

The node can work in two different ways:

• with Running window disabled, the computation is based on the configured Number of Samples;
• with Running window enabled, the computation is performed on the samples received within the configured moving time window.

The result of the selected computation is then sent to the Output connector.

The Computation property defines how the selected input samples are processed.

The available methods are:

When Computation is set to Average, the node calculates the arithmetic mean of the considered samples.

For example, with:

Number of Samples = 4

and the following values:

the resulting output is:

Output = (20 + 22 + 21 + 25) / 4 = 22

The Average method is useful when small fluctuations in the input signal should be reduced.

When Computation is set to Min, the node returns the lowest value among the considered samples.

Using the same values:

the resulting output is:

Output = 20

This method is useful when the lowest value reached during the considered interval is required.

When Computation is set to Max, the node returns the highest value among the considered samples.

Using the same values:

the resulting output is:

Output = 25

This method is useful when the highest value reached during the considered interval is required.

When Running window is disabled, the Number of Samples property defines how many input values are used for the selected computation.

For example:

For the Average method, a larger number of samples generally produces a smoother output.

For Min and Max, the configured number of samples defines how many values are considered when searching for the minimum or maximum value.

The Running window property changes the way the node selects the samples used for the computation.

When Running window is disabled, the node processes the configured Number of Samples.

When Running window is enabled, the computation is performed on the samples received within a moving time window.

The duration of the window is defined using:

• Period UoM, which defines the time unit;
• Time factor, which defines the duration expressed in the selected unit.

The available units for Period UoM are:

• Milliseconds
• Seconds
• Minutes
• Hours

For example:

the node processes the samples received during the last 1 minute.

If:

Computation = Average

the node returns the average of the samples received during the last minute.

If:

Computation = Min

the node returns the minimum value received during the last minute.

If:

Computation = Max

the node returns the maximum value received during the last minute.

The number of samples considered inside the running window is limited to:

100 samples

Consider a temperature sensor whose measured value changes slightly at every acquisition:

With:

the resulting value is:

Output = 22.0°C

Instead of propagating every small variation directly to the following logic, the Time Base Filter provides a more stable value.

Assume:

During the last minute the following values are received:

20, 22, 25, 21, 23

The resulting output is:

Output = 25

After enough time has passed for the value 25 to leave the one-minute running window, it is no longer considered in the computation.

The output is then recalculated using only the values still present inside the active time window.

The Time Base Filter is useful when analog data must be processed over multiple samples or over a time interval.

Typical applications include:

• smoothing temperature sensor values;
• reducing fluctuations in humidity or environmental measurements;
• calculating an average value over a set of samples;
• determining the minimum value reached during a time interval;
• determining the maximum value reached during a time interval;
• stabilizing analog values before comparisons or calculations;
• monitoring minimum or maximum process values over a moving time window.

The Time Base Filter can be tested using the Logic Module simulation tools.

A typical test procedure is the following:

• connect a variable analog value to the Input connector;
• select Average, Min or Max in the Computation property;
• configure the Number of Samples;
• enable Running window if required;
• configure Period UoM and Time factor when using the running window;
• start the simulation;
• provide different values to the Input connector;
• observe how the Output changes according to the selected computation;
• compare the behaviour using different numbers of samples;
• if Running window is enabled, verify that values outside the configured time window are no longer considered.

• Select Average when a smoother representative value is required.
• Select Min when the lowest value among the considered samples is required.
• Select Max when the highest value among the considered samples is required.
• With Running window disabled, use Number of Samples to define how many values contribute to the computation.
• With Running window enabled, use Period UoM and Time factor to define the duration of the moving time window.
• Available Period UoM values are Milliseconds, Seconds, Minutes and Hours.
• The running window supports a maximum of 100 samples.
• A larger sample set generally makes Average filtering more stable but less responsive to rapid changes.
• Consider the dynamics of the measured value when configuring the filter.
• Avoid excessive filtering when rapid input variations must be detected immediately.
• The Output remains an analog value and can therefore be connected directly to other analog Logic Module nodes.

• Logic Module
• Logic Module - Simulation management