Instruction manual
Unsigned Compares
76
890USE18300 September 2003
Greater-than-threshold Unsigned Compare Block
Summary A greater-than-threshold unsigned compare block performs a comparison between
an analog input value and a threshold value (TH). The input value is represented as
an integer in the range 0 to 65 535. The software lets you configure the TH 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
Greater-than-
threshold
Compare Block
A block diagram for a greater-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)—a threshold value against which the operational input value will be
compared and a ∆ for hysteresis around the threshold value. You must specify these
presets.
The output is a Boolean 1 when the operational input is greater than TH + ∆ and a
Boolean 0 when the input is less than or equal to the TH - ∆. The output remains
unchanged when the operational input is greater than TH - ∆ but less than or equal
to TH + ∆.
Enable Input A greater-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 +/-
∆