Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 28)

Publication 1757-UM006A-EN-P - May 2002
1-14 The Fieldbus Communication Model
Table 1.F Bias/Gain Block Specifications
Description The Bias/Gain function block can be used for biased external feedforward control or to set several unit controllers,
such as boiler masters, from one controller output, such as a plant master. A functional schematic of the block is
shown in Figure 1.6 for reference.
Function Notes
• Supports Out of Service (OOS), Initialization Manual (IMan) Local Override (LO), Manual (Man), Automatic (Auto),
Cascade (Cas), and Remote Cascade (RCas) modes.
• The output supports the track algorithm.
• The Balance Ramp option is supported.
• The CONTROL_OPTS selection Act on IR determines whether initialization requests are to be passed on or acted
on locally by changing the BIAS value.
• If the Act on IR option is false, a status of Not Invited (NI) or Initialization Request (IR) at BKCAL_IN will be passed
to BKCAL_OUT. The BKCAL_OUT value will be calculated from the value of BKCAL_IN adjusted for SP and GAIN,
as determined by the control or process status of IN_1. When the upstream block sends an Initialization
Acknowledge (IA) status, this block will send IA status, since its output will now be nearly equal to the value of
BKCAL_IN.
• If the Act on IR option is true, a status of NI or IR at BKCAL_IN results in an adjustment to SP to balance OUT to
the value of BKCAL_IN. The IA status can be sent as soon as IR is detected. BKCAL_OUT will not request
initialization.
• The TRK_VAL input brings in an external value or uses a constant. The TRK_SCALE values convert the TRK_VAL to
a percent of output span value. If the CONTROL_OPTS Track Enable selection is true and TRK_IN_D is true, the
converted TRK_VAL replaces the output (OUT), when the block is in Automatic, Cascade, or Remote Cascade
mode. The CONTROL_OPTS Track in Manual selection must be true for this to occur in Manual mode. If the actual
mode is OOS or IMan, the track request is ignored.
• If the TRK_VAL replaces the OUT, its status becomes Locked Out with Limits set to Constant. The actual mode
goes to LO. The status of RCAS_OUT goes to Not Invited (NI), if not already there.
• If the status of TRK_IN_D is Bad, its last usable value will be maintained and acted upon. If the device restarts,
losing the last usable value, it will be set to false.
• If the status of TRK_VAL is Bad, the last usable value will be used. If there is no last usable value, the present
value of the OUT will be used.
Equation Options In Automatic mode: OUT = (IN_1 + SP) x GAIN
If IN_1 has Non-Cascade status: BKCAL_OUT = (BKCAL_IN / GAIN) - IN_1
If IN_1 has Cascade status: BKCAL_OUT = (BKCAL_IN / GAIN) - SP
Parameters
(see Appendix A for
definitions of each
parameter) ALERT_KEY
BAL_TIME
BKCAL_IN
BKCAL_OUT
BLOCK_ALM
BLOCK_ERR
CAS_IN
CONTROL_OPTS GAIN
GRANT_DENY
IN_1
MODE_BLK
OUT
OUT_HI_LIM
OUT_LO_LIM
OUT_SCALE RCAS_IN
RCAS_OUT
SHED_OPT
SP
SP_HI_LIM
SP_LO_LIM
SP_RATE_DN
SP_RATE_UP ST_REV
STATUS_OPTS
STRATEGY
TAG_DESC
TRK_IN_D
TRK_SCALE
TRK_VAL
UPDATE_EVT