Digital Filter Function Block

The DigitalFilter function block is used for smoothing / filtering values. Values such as outdoor temperature, supply temperature, supply and exhaust air volume flow or brightness can be smoothed / filtered. The filter works for fast changing (duct pressure) and slow changing values (outside air temperature). This allows the stabilization of fluctuations in measured values. The output can be initialized to zero or to the first valid input value read in the first DDC cycle after power up. The function block internally remembers the last Out value which is necessary for the calculation of the new Out value in the next DDC cycle.

Figure 1: DigitalFilter Function Block

Figure 2: DigitalFilter Property Sheet

Inputs

Input Name

Description

In

The In value is the base for the output Out. The output Out follows the In considering the Filter Type and the Time parameter.

If In has a value of "null","+inf" or "-inf", then Out is set immediately to the In value irrespective of the Filter Type and the Time.

Similarly, if In changes from "null","+inf" or "-inf", to a valid value; the valid value is immediately set on Out.

Note: If a temperature value is connected at the input In, which is read in via a Ui Terminal, this value can have the value +-inf/-inf for Sensor Open/Short. The +-inf values are immediately passed to the output Out.

Numeric: 32-Bit floating Point value.

Table 1: Inputs of Digital Filter Function

Output

Output Name

Description

Out

Output filtered value.

Numeric: 32-Bit floating Point value.

Table 2: Output of Digital Filter Function

Parameters

Parameter Name

Description

Filter Type

0 = PT1 filter

Numeric: 32-Bit Numeric value: 0-32, Default: 0.

Time

Filter time constant (Sec).

Numeric: 32-Bit Integer value: 1-65535, Default: 1.

Initialise

False = Initialize the filter with first valid input value

True = Initialize the filter with value 0.

Default: False

Out Save

Master Sync Enabled: If you set it to "true" the last output will be set as output for one cycle after the controller restarts. The application can use it to return to the same state before the controller restart.

Out: To enable or disable the Out feature.

Table 3: Parameters of Digital Filter Function

Examples

Filter In =15, Out =15, Filter Type =0, Time=10Secs Initialize=1 (True). The below picture shows the value 0f 11.30 after 7 Secs of an execution.

Figure 3: Example DigitalFilter Function Block

Filter In =20, Out =20, Filter Type =0, Time=10Secs Initialize=1 (True). The below picture shows the value 0f 11.30 after 8.5 Secs of an execution.

Figure 4: Example DigitalFilter Function Block

Refer to General Description for general information about IRM N4 Function Blocks.