Siemens Ladder logic input contacts and output coils allow simple logical decisions. Functions extend basic ladder logic to allow other types of control. For example, The addition of timer and counters allows event based control. A longer list of function is shown in chart below.
Combinatorial Logic
-relay contacts and coils.: these logic helps us to complete our project with our control by using relays, switches, coils, latches etc.
Events
-Timer instruction: These operate to delay the program. We simply arrange events on our desired time
-Counter instruction: These function also delays time but it operates on counting property to arrange events.
Data Handling
-Moves: We can move one data from a location to another by using Move function.
-Mathematics: We also can operate various mathematics function like addition, subtraction, multiplication, division etc.
-Conversion: we can convert our desired data in binary, octal, hexadecimal or other by using conversion function.
Numerical Logic
-Boolean operation: There are various Boolean operation by which we can operate our program.
-comparison: We can compare our results or data by using comparison instruction.
Lists
-Shift registers/Stacks: These are properties to arrange our data in memories. Register stores data and stacks stores address normally.
-Sequencers: It manages the stored data in registers in proper manner so we can use it anytime easily.
Program control
-Branching/Looping: We can make loop in our program or branch it as required by programmer.
-Immediate input/output: The real time operation is possible in plc.
-Fault/Interrupt detection: There a program is compiled and detects faults or any interruption so we can easily make correction.
Input and output
-PID: Proportional integral derivative is the controller which looks in present status of program, integrates past errors & eliminates them and Looks in future prediction of signaling, errors, conditions etc.
-Communication: The inputs can be given through communication device like we can program in SCADA and communicate to plc as input by communication device.
-High speed counters: These are very useful in plants as we required a quick output and results. It can control high speed inputs and outputs and process it function quickly.
-ASCII string functions: ASCII string code can be given as input so we can operate any program without knowing its internal program. Like a input of counter is named a string I. When any press I then it operates but operator may or may not know which switch (X0 or X1 or ….) is pressed.
Most of these functions use PLC memory locations to get values, store values and track function status. Most functions normally become active when the input is true. But some functions, such as TOF timers, can remain active when the input is off. Other functions only operate after input goes from false to true, this is known as positive edge triggered. Consider a counter that only counts when the input goes from false to true, the length of time the input is true does not change the function behavior. The negative edge trigger function would be triggered when the input goes from true to false. Most functions are not edge triggered: unless stated assume functions are not edge triggered.
Today we also discuss Data handling Move function in next blog. Study above theories so you can understand the next functions easily.
No comments:
Post a Comment