Honeywell HC900 Safety Manual page 32

Design and Implementation of HC900 Control System - Allowable Function Blocks for Process and Safety Functions
Provides 16 digital outputs in groups of four. A
Four Selector dedicated display allows activating of only one output
Switch
per group while other outputs in the associated group
are turned off.
The Hand – Off – Auto (HOA) switch function block
permits state change requests from a Local Operator
Interface or a Remote source. The block states are:
BYPASS (external manual operation of a device),
Hand (manual operation from an operator interface),
Hand/Off/Auto
Auto (default – requests are operated automatically),
Switch
or Off (relay to be switched to Bypass, Hand, or
Auto). The HOA switch is also used with the Device
Control (DC) function block to comprise a Pump
Control algorithm which is used to manipulate the
state of a controlled device (pump).
Each sequencer supports up to 16 digital outputs that
may be either on or off in each of 50 states e.g.
PURGE, FILL, HEAT, etc, per block The sequencer
may have up to 64 sequential steps that activate
within the states of the process. Steps of the
sequencer may be configured to advance based on
time, on digital event (2 per step), or a manual
advance. A separate jog function is also provided.
The function can also configure an analog output on a
step basis. The operational sequence for the steps is
Sequencer
retained in a separate sequence file in the memory of
the controller that may be selected on-demand
through a user interface or via a recipe. ATTENTION:
If either or both NSEQ and NSTEP are connected
directly to analog variables, when that analog variable
changes (for example: via a recipe load), then the
Sequencer block will immediately use the new value
internally. If NSEQ or NSTEP is connected to any
other function type then their values are loaded into
the Sequencer only when ^SET goes through a
positive transition.
Counters/Timers
Blocks
24 HC900 Process & Safety Controller Safety Manual
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Revision 1.9
01/14