Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual User Manual
Page 26
Publication 1757-UM006A-EN-P - May 2002
1-12 The Fieldbus Communication Model
Table 1.E Analog Output Specifications
Description
The Analog Output function block converts the set point (SP) value to a number that can be used by the hardware
associated with the CHANNEL selection. A functional schematic of the block is shown in Figure 1.5 for reference.
Function Notes
• Can use either the Set point (SP) value after limiting or the Process Variable (PV) value for the BKCAL_OUT value.
• Supports Out of Service (OOS), Local Override (LO), Manual (Man), Automatic (Auto), Cascade (Cas), and Remote
Cascade (RCas) modes.
• The conversion of Set point (SP) to percent of span is based on the PV_SCALE range.
• The conversion of the percent of span to a compatible value for the hardware is based on the XD_SCALE range.
• Use the Increase to Close Option in IO_OPTS to invert the span.
• Use the Cascade mode to transfer the output of another block to the Set point of the AO block.
• If the hardware, such as a valve positioner, supports a readback value, run this value backwards through the XD
scaling to act as the PV for this block. If this is not supported, READBACK is generated from OUT.
• In the Man mode, an operator can write a value to OUT. A manufacturer must put operational limits in the
Transducer, where an operator cannot access them, to permit the Man mode. If Man mode is not permitted, it must
be supported as a transition mode for exiting the OOS mode
• The SIMULATE parameter is for testing purposes only and always initializes in the disabled state.
Equation Options
Temp = (SP - EU@0%) / (EU@100% - EU@0%) [PV_SCALE]
OUT = Temp x (EU@100% - EU@0%) + EU@0% [XD_SCALE]
Temp = (READBACK - EU@0%) / (EU@100% - EU@0%) [XD_SCALE]
PV = Temp x (EU@100% - EU@0%) + EU@0% [PV_SCALE]
Parameters
(see Appendix A
for definitions of
each parameter)
ALERT_KEY
BKCAL_OUT
BLOCK_ALM
BLOCK_ERR
CAS_IN
CHANNEL
FSAFE_TIME
FSAFE_VAL
GRANT_DENY
IO_OPTS
MODE_BLK
OUT
PV
PV_SCALE
RCAS_IN
RCAS_OUT
READBACK
SHED_OPT
SIMULATE
SP
SP_HI_LIM
SP_LO_LIM
SP_RATE_DN
SP_RATE_UP
ST_REV
STATUS_OPTS
STRATEGY
TAG_DESC
UPDATE_EVT
XD_SCALE