Design and Implementation of HC900 Control System - Allowable Function Blocks for Process and Safety Functions
Revision 1.9 HC900 Process & Safety Controller Safety Manual 25
01/14
Resettable Timer
The Resettable Timer block has the following
attributes: Provides increasing or decreasing timing
base on an enable input. Increasing time from 0 or
preload value. Decreasing time from preset or
preload value. Increasing time provides digital output
upon reaching preset. Decreasing time provides
digital output upon reaching zero. Reset input sets
increasing timer to zero. Reset input sets decreasing
timer to preset value. Preset value may be internal, or
remote via a dedicated input. Inc./Dec. selection is via
digital input. Toggling the reset (RST) pin resets the
current elapsed time and loads the new preset value;
therefore, if changing the preset value (remote or
local), the user must enter the new preset value, then
reset the timer for the new preset to be used during
the next time cycle. If the timer is reset prior to
entering the new preset value, the timer will use its
previous preset for its compare condition.
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Periodic Timer
Function (1 or 2) –
1. Time/Cycle: Generates a discrete output pulse at a
specified start time based on the real-time clock and
at specified time periods thereafter. Start Times =
Month, Day, Hour, Minute, Second. Cycle Periods =
Monthly, Weekly, Daily. Time Cycle Periods within a
Day = Hours (0-23) Minutes (0-59) Seconds (0-59).
Note: Once started, period repeats until reset.
2. Reset Cycle: Generates a digital output based on a
digital input and at regular intervals thereafter. Time
Start = ON to OFF transition of reset input. Cycle
Time Period = Hours (0-23) Minutes (0-59) Seconds
(0-59).
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Up/Down Counter
The output counts the number of rising edge logic
transactions on the input to the block up to a preset
value (RPRE or LPRE). When the preset value is
reached, a logic output (PREI) is enabled until a
Reset input (RST) resets the block. A Reset input
(RST) resets the block. Value may be set to increase
to the preset value or decrease from the preset value.
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Off-Delay Timer
Provides an OFF state logic output delayed by a user
specified delay time after an ON to OFF transition of
the RESET input. An OFF to ON transition of the
RESET input before the delay time has elapsed
causes the timer to reset. Transitions from OFF to ON
of the input are not delayed. If RESET is ON, then
OUT = ON. If previous RESET input is ON and
RESET is OFF, then TIMER = DELAY. If RESET is
OFF and TIMER is not 0, then time = TIMER 1. If
RESET is OFF and TIMER is 0, then OUT = OFF
(delay time is reset).
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