Honeywell HC900 Reference Manual page 112

Function Blocks
CARB Carbon Potential Function Block
MDRQI = External Mode request (typically connected to the MDRQO output of a MDSW function block
that encodes discrete switch inputs).
0 = No Change
1 = Manual Mode Request
2 = Auto Mode Request
4 = Local Setpoint Request
8 = Remote Setpoint Request
BCI = Back Calculation Input Value—See ATTENTION 1.
Output
PV = Calculated Process Variable (% Carbon) for monitoring
DEWPT = Calculated Dewpoint
WSP = Working Setpoint in Engineering Units for monitoring (setpoint in use)
AL1 = Alarm 1 - Digital Signal
AL2 = Alarm 2 - Digital Signal
DIRECT = ON = Direct; OFF = Reverse
ATI = Autotune Indicator (ON = Autotune in Progress)
MODE = Loop mode status (typically connected to the Mode Flags block for encoding). Value indicates
mode as follows:
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
BCO - Back Calculation Output (for blocks used as Cascade Secondary)—See ATTENTION 2.
ATTENTION
1.
When a request to change from Auto to manual is received and:
− the request comes from the operator Interface, the request is ignored.
− the request comes from the Mode Switch (MDSW) function block, the request is retained
2.
BCO output is provided for applications where the block is used as a cascade secondary.
BCI input is provided for applications where the block is used as a cascade primary. When
the BCO output of a secondary loop is connected to the BCI input of a primary loop,
bumpless transfer is achieved when the secondary is switched into remote setpoint (i.e.,
cascade) mode. In addition, the primary loop is prevented from reset windup when the
secondary is decoupled from the process. The secondary is decoupled from the process
when it is in local setpoint mode or manual output mode, has reached a setpoint or output
limit, or is integral limiting because its BCI input. For example, see
98
RSP AUTO
RSP MAN
RSP Initialization Manual (See ATTENTION 1)
RSP Local Override (See ATTENTION 1)
LSP AUTO
LSP MAN
LSP Initialization Manual (See ATTENTION 1)
LSP Local Override (See ATTENTION 1)
and when leaving the Initialization Mode or Local Override Mode the loop will go to
manual.
HC900 Hybrid Control Designer Function Block Reference Guide
F igure 73.
H
Revision 11
2/07