Rockwell Automation 6723-PCO DATA PROCESS CONFIG OPERATIO - Manual (Page 5)

Process Configuration and Operation Software for Windows t 3
Publication 6723Ć10.1 Ć August 1996
Throughout this Quick Start, we will focus on the development of a
grain-drying application. By following this example through from
start to finish, you will be able to get a feel for the development of a
typical process control application. In the interest of clarity, we will
keep this example as simple as possible.
Grain-drying applications are used to dry grain for storage before its
use. In these applications, it is very important that the control system
have the ability to control air and temperature loops independently;
proper drying temperature must be maintained despite changes in the
ambient temperature in unheated buildings or variations in drying air
flow. Furthermore, temperature or heat must be applied to the air to
ensure that moisture is removed by the time the grain reaches the end
of the dryer, or the storage bin.
Air flow must also be maintained above a minimum level so as to
ensure complete moisture removal and avoid hot spots that could
brown the grain, but not exceed a high flow that would blow grain
off the line.
HS
103
FT
100
FE
100
FIC
100
TT
101
TE
101
TIC
101
TY
101
conveyor M
SCR
2 Regulatory Loops
Ć Flow loop (100)
Ć Temperature loop (101)
2 Analog in (4Ć20 mA)
2 Analog out (4Ć20 mA)
Conveyor control (103)
Ć Auto/Manual
Interlocks
Ć Temperature loop
FY
100
For the purposes of this application example, we can assume the
following specific control requirements:
•
Loop control must include complete Auto/Manual control (e.g.
bumpless mode transfers, anti-reset windup, alarms on PV,
setpoint ramping, etc.).
•
Process measurement and control equipment is 4-20 mA.
The temperature loop must be interlocked with air flow to prevent
browning (or, in the worst case, a fire) if the air flow is less than a
specified minimum, or if the temperature is greater than a
specified maximum.
•
Conveyor control is On/Off control, and is normally controlled
from the PLC logic.
In addition, the operator must be able to control the motors in a
Manual mode from the supervisory station.
Overview of the ForcedĆAir
GrainĆDrying Application
Example