Design and Implementation of HC900 Control System - Allowable Function Blocks for Process and Safety Functions
Revision 1.9 HC900 Process & Safety Controller Safety Manual 19
01/14
Pulse Output
This function block generates a pulse train of a
specified number of pulses following a start
instruction. The pulse frequency is selectable. The
output controls an output transistor on a
Pulse/Frequency/Quadrature module. The number of
pulses remaining following a start instruction is
provided on the output pin.
X
Quadrature Input
This function block measures/controls movement of
an actuated device. A digital encoder connected to
the actuated device produces two channels (A and B)
of square waves, offset 90 degrees. Quadrature
refers to the 4 logic states between these two waves.
The rising edge to rising edge (cycle) on channel A or
B indicates that one set of bars on the encoder have
passed by its optical sensor. By counting these
passing rising edges the Quadrature block measures
1) distance (or whatever engineering units are being
controlled by the device), 2) position (that is, distance
from a marker designated as zero), 3) direction
(indicated by the sequence between the two
channels; A leads B or B leads A). More precise
measurement/control is done by counting more logic
states determined by the two waves. For example,
the quadrature state of channels A and B create four
unique logic states. When these four unique logic
states are decoded, the resolution obtained is 4 times
(4X) the resolution of the encoder. So with this in
mind 250 cycles would yield 1000 quadrature states.
X
Loop Blocks
PID
Provides Proportional (P, Integral (I and Derivative
(D, (3-mode) control action based on the deviation or
error signal created by the difference between the
setpoint (SP) and the Process Variable analog input
value (PV).
X
On Off
Provide ON/OFF control. The output is either ON
(100%) or OFF (0%).
X
X
Carbon Potential
A combined Carbon Potential and PID algorithm
determines Carbon Potential of furnace atmospheres
based on a Zirconium probe input.
X
Loop Switch
Digital interface to control loops to initiate autotuning,
change control action, force bumpless transfer, and
select tuning set. It connects to a PID, TPSC, or
CARB function block.
X
Mode Switch
Digital interface to control loops to select automatic or
manual modes and/or local or remote setpoint.
Connects to PID, ON/OFF, CARB, or TPSC mode
block input.
X
X
Mode Flags
Turns ON the output that corresponds to the current
value of MODE. Turns OFF all other outputs.
X
X
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