Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 40)

Publication 1757-UM006A-EN-P - May 2002
1-26 The Fieldbus Communication Model
Function Notes
(cont.)
• The full cascade SP sub-function is used, with rate and absolute limits. Additional control options are available to
have the SP value track the PV value, when the block's actual mode is IMan, LO, Man, or ROut. Limits do not cause
SP-PV tracking.
• Use the Act on IR CONTROL_OPTS to select whether to pass initialization requests or act on them locally by
changing the SP value. If this option is OFF or to pass, 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 BKCALC_IN
divided by GAIN and IN_1. When the upstream block sends Initialization Acknowledge (IA) status, the block sends
the IA status, since its output will now be nearly identical to the value BKCAL_IN. If this option is ON or to act, a
status of NI or IR at BKCAL_IN adjusts the SP to balance the output to the value of BKCAL_IN. The IA status is sent
as soon as IR is detected. The BKCAL_OUT will not request initialization.
• Use the Balance Ramp CONTROL_OPTS to maintain the ratio SP value, when the block is in Manual (Man) mode.
An internal value follows the actual value required to maintain balance. When block mode changes to Automatic
(Auto), the internal value ramps to zero contribution in BAL_TIME seconds. If Balance Ramp option is OFF or not
used, the ratio SP value immediately changes to follow the changes to the input or output, when the block is in
Man mode.
• 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 (Auto), Cascade (Cas), or Remote
Cascade (RCas) 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 BKCAL_OUT, and 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.
• Use the Obey SP limits if Cas or RCas CONTROL_OPTS to use SP value after limiting in Cas or RCas mode.
• Use the “Use PV for BKCAL_OUT” CONTROL_OPTS to the PV value for the BKCAL_OUT value.
Equation Options If Auto mode, OUT = IN_1 (filtered) x SP x GAIN
PV = IN (filtered) / IN_1 (filtered) / GAIN
If IN_1 has non-cascade status, BKCAL_OUT = BKCAL_IN / GAIN / IN_1 (filtered)
If IN_1 has cascade status, BKCAL_OUT = BKCAL_IN / GAIN / SP
Parameters
(see Appendix A
for definitions of
each parameter) ACK_OPTION
ALARM_HYS
ALARM_SUM
ALERT_KEY
BAL_TIME
BKCAL_IN
BKCAL_OUT
BLOCK_ALM
BLOCK_ERR
CAS_IN
CONTROL_OPTS
DV_HI_ALM
DV_HI_LIM
DV_HI_PRI
DV_LO_ALM DV_LO_LIM
DV_LO_PRI
GAIN
GRANT_DENY
HI_ALM
HI_HI_ALM
HI_HI_LIM
HI_HI_PRI
HI_LIM
HI_PRI
IN
IN_1
LO_ALM
LO_LIM
LO_LO_ALM LO_LO_LIM
LO_LO_PRI
LO_PRI
MODE_BLK
OUT
OUT_HI_LIM
OUT_LO_LIM
OUT_SCALE
PV
PV_FTIME
PV_SCALE
RA_FTIME
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
Table 1.M Ratio Block Specifications