Instruction manual

Integer Compares

890USE18300 September 2003

Less-than-threshold Integer Compare Block

Summary A less-than-threshold integer compare performs a comparison between an analog

input value and a threshold value that you specify. The analog input value is

represented as an integer in the range -32 768 to +32 767. The software allows you

to assign a delta (∆), which acts as an hysteresis around the threshold value. The

block produces a Boolean result as its output.

Structure of a

Less-than-

threshold

Compare Block

A block diagram for a less-than-threshold integer compare is shown below:

The block has two inputs—an enable input and one operational input. The enable

input turns the block on or off. The operational input sends a word value to the block

that will be compared against the threshold.

The block also has two preset values (See Configuring Preset Values for a Reflex

Block, p. 27)—a threshold value against which the operational input value will be

compared and a ∆ for hysteresis around the threshold. You must specify these

presets.

The output is a Boolean 1 when the operational input value is less than threshold -

∆ and a Boolean 0 when the input is greater than or equal to threshold + ∆. The

output remains unchanged when the operational input is greater than or equal to

threshold - ∆ and less than threshold + ∆.

Enable Input A less-than-threshold compare block is enabled either by a Boolean 1 or an always

enabled constant. It can be disabled by a Boolean 0 or an always disabled constant.

If the enable input is a Boolean, it may be produced by:

a digital input from a module on the island

a digital output from the virtual module (See The Virtual Module, p. 28)

an output on the action module (See Using the Action Module as an Input to a

Block, p. 32) written to by the fieldbus master

When the enable input is a Boolean 0 or an always disabled constant, the block is

disabled—the action does not execute and the output is frozen in the state it was in

when the block became disabled. The block continues to process inputs but does

not act on them. If the block becomes enabled, it immediately begins acting on the

latest set of inputs received.

output

enable

operational input

less than threshold compare

threshold +/-

∆