Design and Implementation of HC900 Control System - Allowable Function Blocks for Process and Safety Functions
30 HC900 Process & Safety Controller Safety Manual Revision 1.9
01/14
System Monitor
(ASYS)
The Analog System Status Block is a function block
and is part of the Alarm/Monitor category. It provides
read access to controller status values including
those related to the Analog execution cycle. The
output may be connected to function block inputs.
The outputs may also be connected to signal tags for
operator interface monitoring. When you click on the
ASYS function block on a diagram, the "Controller
System Parameters" dialog box opens. The 50 or 60
Hz selection is used to establish the integration times
for analog to digital conversion. This is needed to
prevent aliasing the line frequency when converting
low level signals such as thermocouples. In the
United States, the line frequency is 60Hz.
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X
IO Rack Monitor
The rack monitor block is a repository for
controller/expansion rack I/O module information,
including diagnostics. The Rack function block
provides Read/Write access to I/O Rack values. This
block is always stored in the reserved block area (96
thru 100), are always in the configuration whether
visible in the FBD or not. The total number is
dependent on the controller type.
X
X
Analog Alarm
The analog alarm block accepts an analog signal as a
process variable and compares it to a user-entered
limit value (setpoint) to determine an alarm condition.
The setpoint may be entered by the user or be
another analog signal in the controller. Alarm actions
may be high, low or high deviation, low deviation or
band deviation. For deviation alarming, a second
analog signal provides the reference and setpoints
represent deviation from the reference. The alarm
output may be inverted to create a normally active
digital output. A user selection for latching until
acknowledged or automatically reset is provided. A
user-specified hysteresis value in the engineering
units of the process variable is provided. An on-delay
time value up to 240 seconds is available to prevent
momentary alarm actions. A digital disable input is
available to disable alarm actions.
X
X
Alarm Group
The Alarm Group Function Block allows you to tie
alarm groups into the Control Strategy. It provides
events for unacknowledged and active user
conditions plus remote acknowledgement of all
alarms in the group. This block is always stored in the
reserved block area (40 thru 59), are always in the
configuration whether visible in the FBD or not, and
all outputs of the block are updated every alarm scan.
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