Comparison Principle with a Main Type

Overview

The compare block with the Main type manages Thresholds, Reflex outputs and Events in the following modes:

oOne-shot

oModulo-loop

oFree-Large

Comparison is configured in the Configuration screen by activating at least one threshold.

Comparison can be used to trigger:

oprogramming action on thresholds

oan event on threshold associated with an external task

oreflex outputs

Principle of a Comparison

The Main type can manage up to 2 thresholds.

A threshold is a configured value that is compared to the current counting value. Thresholds are used to define up to 3 zones or to react to a value crossing.

They are defined by configuration and can also be adjusted in the application program by using the HSCSetParam function block.

If Thresholdx (x= 0, 1) is configured and comparison is enabled (EN_Compare = TRUE), output pin THx of the function block is:

oOption 1:

Counting Up – Reflex Output x is TRUE when value < TH0 (reset when value = TH0).

Counting Down – Reflex Output x is TRUE when value ≤TH0 (set when value = TH0).

oOption 2:

Counting Up – Reflex Output x is TRUE when TH0 ≤ value < TH1 (set when value= TH0 and reset when value = TH1).

Counting Down – Reflex Output x is TRUE when TH0 < value ≤ TH1 (set when value = TH1 and reset when value = TH0).

oOption 3:

Counting Up – Reflex Output x is TRUE when value ≥TH1 (set when value = TH1).

Counting Down – Reflex Output x is TRUE when value > TH1 (reset when value =TH1).

NOTE: When EN_Compare is set to FALSE on function block, comparison functions are disabled, including external tasks triggered by a threshold event and Reflex outputs.

This diagram shows the state of the Reflex Output (fast digital output) for each individual option:

 

 

Threshold Behavior

TH0 and TH1 are managed by the task and are updated at the rate of the task cycle time.

Configuring Event

Configuring an event on threshold crossing allows to trigger an external task. You can choose to trigger an event when a configured threshold is crossed downward, upward, or both ways.

When the HSC is counting:

oup, the configured External Event Task is triggered when the counting value = Threshold value + 1

odown, the configured External Event Task is triggered when the counting value = Threshold value - 1

If overflow or underflow, no External Event Task is triggered.

Reflex Output Behavior

Configuring reflex outputs allows to trigger physical reflex outputs.

These outputs are not controlled in the task context, reducing the reaction time to a minimum. This is convenient for operations that need fast execution.

Outputs used by the High Speed Counter can only be accessed through the function block. They cannot be read or written directly within the application.

NOTE: The state of the reflex outputs depends on the configuration.

Changing the Threshold Values

The TH0, TH1, Reflex0, Reflex1, Out0 and Out1 as well as physical outputs will operate with respect to the threshold values, even when the threshold values are dynamically changed as long as SuspendCompare= TRUE.

Therefore, care must be exercised when threshold compares are active to avoid unintended or unexpected results from the physical reflex outputs and HSCMain function block outputs. If the compare function is disabled, threshold values can be modified without worry of unintended outputs. However, if the compare function is enabled, you must, at least, suspend the threshold compare function while modifying the threshold values.