Instruction manual
Unsigned Compares
72
890USE18300 September 2003
Less-than-threshold Unsigned Compare Block
Summary A less-than-threshold unsigned compare block performs a comparison between an
analog input value and a threshold value. The input value is represented as an
integer in the range 0 to 65 535. The software lets you assign the threshold value
along with a delta (∆) value, which acts as an hysteresis for the threshold. The action
produces a Boolean result as its output.
Structure of a
Less-than-
threshold
Comparison
Block
A block diagram for a less-than-threshold unsigned 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), which you must specify—a threshold value against which the
operational input value will be compared and a ∆ for hysteresis around the threshold
value.
The output is a Boolean 1 when the operational input 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 TH - ∆ but
less than TH + ∆.
Enable Input A less-than-threshold unsigned compare block can be 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 +/-
∆