Function Block Programming
Function block is ideal for application that use a lot of analog control
functions, in the process industry, where you will find analog for
temperature, flow, and level control etc .function block programming
has the ability to control different properties and parameters of
particular function with in a single function
Function Block
Elements
INPUT REFERENCE (IREF): supply a value from an
input device or tag
OUTPUT REFERENCE (OREF): send a value to an
output device or tag
FUNCTION BLOCK: perform an operation on an input
value or values and produce an output value or values
OUTPUT WIRE CONNECTOR (OCON) / INPUT WIRE
CONNECTOR (ICON): transfer data between function
blocks when they are:1. far apart on the same sheet 2.
on different sheets within the same routine 3. disperse
data to several points in the routine
Latching data / Order of
Execution
Latching Data: data in that IREF is latched for the
scan of the function block routine. controller updates
all IREF data at the beginning of each scan.
Order of Execution: is determined when verified or
download to controller
With sequentially blocks, the execution order moves
from input to output indicator.
Execution order is only relative to the blocks that are wired
together.
To identify which block to execute first, mark the input wire
that creates the loop (the feedback wire) with the Assume
Data Available
D2SD Example
Example
The D2SD instruction is typically used to control on-off or open-close
devices such as pumps or solenoid valves. In this example, the D2SD
instruction controls a solenoid valve adding corn syrup to a batch tank. As
long as the D2SD instruction is in Program control, the valve opens when
the AddSyrup input is set. The operator can also take Operator control of
the valve to open or close it if necessary The solenoid valve in this
example has limit switches that indicate when the valve is fully closed or
opened. These switches are wired into the FB0 and FB1 feedback inputs.
This allows the D2SD instruction to generate a FaultAlarm if the solenoid
valve does not reach the commanded state within the configured Fault
Time.
Select (SEL)
The SEL instruction uses a digital input to select one of
two inputs
The SEL instruction selects In1 or In2 based on SelectorIn.
If SelectorIn is set, the instruction sets Out = In2.
If SelectorIn is cleared, the instruction sets Out = In1.
Out becomes an input parameter for function_block_C.
Selected Summer (SSUM)
The SSUM instruction uses Boolean inputs to select
real inputs to be algebraically summed
The values of select1 and select 2 determine whether to
select analogInput1 and analog_input2, respectively.
The instruction then adds the selected inputs and places the
result in Out. Out becomes an input parameter
forfunction_block_C.
Function Block (FB)
Function Blocks are the basic elements of a control
system. Function Blocks consist of two parts; a set of
input and output parameters and an algorithm specific to
the specific type of function block. Function Block
language is designed to control “parameter areas”.
Function Block is natively suited for continuous
processes with analog values such as PID Loops
Function Block Diagram (FBD) Language
• Graphical Free-form drawing / programming environment
– Place instructions blocks and draw connections to pass parameters
– Position and organize blocks based on application to improve readability
– Floating text boxes provide application documentation (Planned for V12)
• Automatic sheet execution order determined by block
interconnections
– Eliminates program creation process
– Simplifies program modification
• Comprehensive FBD functions
are native inside the Logix5000
– Common LD blocks in FBD
– 42 new process and drive
control functions
• ActiveX faceplates for key
FBD blocks streamline HMI
development
Applications for Function Block Diagram
• Ideal for analog loop control algorithms
–
–
–
–
Graphically represents control loops
Highly visual language is easy to understand
Resembles circuit diagrams
Commonly used in Distributed Process
Systems (DCS)
• Continuous or Batch Process control
loops
• Drive control loops
– Speed, position, and tension regulation…
– Rewind, winder, and dance control…
– Provide a foundation for applications that
previously used the Reliance Automax
Process Control
– Found in many manufacturing, motion and packaging applications.
Robotic assembly, such as that found in automotive production, can be
characterized as discrete process control. Most discrete manufacturing involves the
production of discrete pieces of product, such as metal stamping.
Batch – Some applications require that specific quantities of raw materials be
combined in specific ways for particular durations to produce an intermediate or
end result. One example is the production of adhesives and glues, which normally
require the mixing of raw materials in a heated vessel for a period of time to form a
quantity of end product. Other important examples are the production of food,
beverages and medicine. Batch processes are generally used to produce a relatively
low to intermediate quantity of product per year (a few pounds to millions of
pounds).
Continuous – Often, a physical system is represented though variables that are
smooth and uninterrupted in time. The control of the water temperature in a heating
jacket, for example, is an example of continuous process control. Some important
continuous processes are the production of fuels, chemicals and plastics.
Continuous processes, in manufacturing, are used to produce very large quantities
of product per year(millions to billions of pounds).
Discrete
Control out put discreet/ analog with a number
of input /output parameter
Feedback Input based on response time
Input upper and lower range
Auto manual modes
Outputs range upper lower
Gain