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

oPeriod Meter

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

Comparison can be used to trigger:

oa programming action on thresholds

oan event on a threshold associated with an external task

NOTE: This option is only available for TM3XF• expansion modules, which support external events.

oreflex outputs.

Principle of a Comparison

The Main type can manage up to four thresholds.

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

Threshold values are defined in the configuration window and can also be adjusted in the application program by using the HSCSetParam_TM3 function block.

If Thresholdx (x= 0, 1, 2, 3) is configured and comparison is enabled (EN_Compare = 1), output pin THx of the HSCMain_TM3 function block is:

oset when counter value >= Thresholdx

oreset when counter value < Thresholdx

NOTE: When EN_Compare is set to 0 on HSCMain_TM3 function block, comparison functions are disabled, including external tasks triggered by a threshold event and Reflex outputs.

The following example for Modulo loop with two thresholds shows comparison in the HSCMain_TM3 function block:

 

 

Configuring Event Triggering in HSC Main Single or Dual Phase

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 as follows:

oUpward Cross. The event is triggered when the measured value goes above the threshold value.

oDownward Cross. The event is triggered when the measured value goes below the threshold value.

oBoth Cross. The event is triggered when the measured value goes above the threshold value and when the measured value goes below the threshold value.

Configuring Event Triggering in Period Meter Mode

Configuring an event allows to trigger an external task. You can choose to trigger an event as follows:

oBelow threshold value. The event is triggered when the measured value is lower than the threshold value.

oAbove threshold value. The event is triggered when the measured value is higher than the threshold value.

oBetween threshold values. The event is triggered when the measured value is between two threshold values.

Threshold Behavior

Using thresholds comparison status available in the task context (TH0 to TH3 output pins of the function block) is suitable for an application tolerant of the inherent lag of cycle times and asynchronism of communications, especially when using the modules over a field bus in distributed architectures.

Configuring Reflex Output

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.

Example of the reflex outputs triggered by threshold:

 

 

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

Changing the Threshold Values

Care must be exercised when threshold compares are active to avoid unintended or unexpected results from the outputs or from sudden Event task execution. If the compare function is disabled, threshold values can be modified freely. However, if the compare function is enabled, suspend at least the threshold compare function while modifying the threshold values.