Tag Archives: PLC ladder diagram

What time relay is used for Mitsubishi PLC power-off delay

Mitsubishi does not have a power-off delay to close the relay. Only the power-on delay closes the relay, but it can be implemented by a program.

as the picture shows,
When X0 is ON,
M0 reset,
M0 is disconnected in front,
T0 does not count,
When X0 becomes OFF,
M0 is set and T0 starts counting.
Time is up,
When the contact T0 is output, the function of closing the power-off delay is reached.

Mitsubishi plc programming Ladder diagram: motor is rotating for 10 seconds, inversion for 8 seconds, cycle

Ladder diagram:

Press X0, M0 is energized and self-locked.
At the same time, KT1 is turned on and Y0 is output. At this time, the motor is rotating 10S.

When the 10S time is up, T1 disconnects YO, and M1 is powered on and locked.

At the same time Y1 output, the motor is reversed.

KT28 seconds to the time, M0 reset, at this time a working cycle is over, automatically enter the next cycle.

Siemens PLC S7 300/400 master relays orders

Main control relay (Master Control Relay), abbreviated as MCR. MCR Master relay command is used to control whether normal execution of the instruction in the region, equivalent to a connect and disconnect the flow of the main switch. MCR instruction is not much used, S7-200 is no MCR instruction.

MCRA to activate the master relay instructions, MCRD to deactivate the master relays orders.

Open the master relays orders MCR< in the MCR before you save the results of logical operations on the stack RLO (MCR), close the master relays orders MCR> MCR saved out of the stack in the RLO. MCR< and MCR> used to indicate controlled temporary power cord formation and termination.

MCR instructions can be nested, MCR the MCR can be another zone. MCR stack is a LIFO stack, allowing the maximum nesting depth of 8 levels.

MCRI0.2 control, I0.2 and MCR MCR in the stack level of the same State. MCR bit is 1 when will perform Q4.0 coil MCR control area and MOVE instructions. MCR bit is 0 when Q4.0 is 0.

Siemens plc S7 300/400 ladder logic blocks in calling instructions

CALL in the ladder diagram coil can call functions (FC) or system functions (SFC), the call cannot be passed parameters. Calls can be unconditional, CALL directly connected to the vertical line on the left side of the coil, equivalent to UC in the statement table orders; can also be conditional, condition provided by the control CALL contact circuits of coils, equivalent to CC in the statement table instructions.

Logical block is called if you need to pass parameters, you can use the command to invoke the function block in the box. FB 3-70 box in Figure 10 is the function that is being invoked, DB3 is called FB 10 o’clock block of background data.

Conditions for return instructions (Return,RET) appears as a coil, left logic for conditional block conditions provided by the contact circuit to control it, RET coil cannot be connected directly on the left of the vertical power cord. If you call it is the unconditional return, at the end of the block does not require the use of RET instruction.

FX2N series PLC position control module

In machine operation, speed and accuracy are often contradictory, in order to improve machine efficiency and increase speed, parking control there is a problem. So it is necessary to control. As a simple example, motor driven mechanical home by starting location, such as at top speed to return, due to the high speed stop inertia, the deviation in the home has to be large, slow down to ensure the accuracy of positioning.

Position control systems, often adopt servo motor and stepping motor driven device. Openloop control and closedloop control can be used. For stepper motors, we can adjust the send speed to change the machine‘s working speed of the pulse. With the FX series PLC, navigate through the pulse output of the unit or module, you can achieve the position of one or more points. FX2N series are described belowpulse output module and the control module.

(1) pulse output module FX2N-1PG. FX2N-1PG pulse generator unit can complete a separate axis of orientation, this is achieved through servo or stepper motor drive amplifier provides a specified number of pulses to achieve. FX2N-1PG is only used for FX2N series, with TO/FROM instruction set various parameters, and speed read out position value. The modules take up to 8 I/O point. Output up to 100kHz the pulse train.

(2) the controller FX2N-10GM. FX2N-10GM for pulse output unit, whether it is a singleaxis positioning unit, not only can handle single-speed, and interrupts location, and can handle complicated control, multi-speed operation. FX2N-10GM can have up to 8 connections on the FX2N series PLC. Maximum output is 200kHz.

(3) positioning controller FX2N-20GM. A FX2N-20GM controlled twoaxis, performs linear interpolation, circular interpolation or independent twoaxis positioning control. Maximum output pulse trains of up to 200kHz (interpolation period, a maximum of 100kHz).

(4) the programmable cam switch FX2N-1RM-E-SET. In the mechanical drive control, often to diagonal position detection, different at different position in terms of conduction, shutdown signal. Used mechanical cam switches, mechanical cam switches and high precision, but easy to wear. FX2N-1RM-E-SET programmable cam switches can be used to replace mechanical cam switches for high precision angle position detection. Complementary angle sensor cable length of up to 100m. Application and other programmable cam switches, brushless resolver high accuracy angle setting and monitoring its internal EEP-ROM, no batteries, can hold up to 8 different programs. FX2N-1RM-E-SET on the FX2N, can also be used independently. FX2N maximum 3. It takes 8 I/O point.

FX2N Series PLC data communication module

PLC communication module is used to complete with other PLC intelligent control, other communication between devices or computers. Following brief introduction to FX serial communication function expansion board, adapter and communication modules.

(1) communication expansion board FX2N-232-BD. FX2N-232-BD is to connect standard PLC and other RS-232C transport device interface board, such as personal computers, bar code reader, or printer. The panels can be installed inside the FX2N extension. The maximum transmission distance is 15m, the maximum baud rate for 19200bit/s. PLC using special software for the extension plate can be running monitoring, can also be transmitted from the PC to the PLC program.

(2) communication interface module FX2N-2321F. FX2N-2321F on connect FX2N series PLC can realize RS-232C with the other fullduplex serial communications interface devices, such as personal computers, printers, bar-code reading device and so on. FX2N series FX2N-2321F modules can connect up to 8 blocks. The module using FROM/TO command to send and receive data. Maximum transmission distance is 15m, the maximum baud rate for 19200bit/s. The modules take up to 8 I/O point. Data length and serial communication baud rate can be set by a special data register.

(3) communication expansion board FX2N-485-BD. FX2N-485-BD for RS-485 communication. It can be applied to no agreement on data transfer, FX2N-485-BD at the time of the original agreement, as a way, using RS instruction in personal computers, barcode reader, printer, data transfer between. Transmitting maximum transmission distance is 50m, the maximum baud rate for 19200bit/s. Each of the FX2N series PLC expansion boards can be fitted with a FX2N-485-BD communication. In addition to using this communication expansion boards and computer communications, it can also be used to achieve two parallel between FX2N series PLC.

(4) communication expansion board FX2N-422-BD. FX2N-422-BD to RS-422 communications, can be connected on the FX2N series PLC, and as a tool for programming or control a port. This interface is available outside of the PLC connected to PLC devices, data storage unit, and human-machine interface. FX2N-422-BD can be used to connect two data storage unit (DU) or DUseries unit and a programming tool, but one can only connect a programming tool. Every basic unit can be connected to a FX2N-422-BD and cannot be used with FX2N-485-BD or FX2N-232-BD.

(5) the interface module MSLSECNET/MINI

Use MSLSECNET/MINI interface module, series PLC of FX series PLC can be used as a local control station, constitute a distributed control system.

Above on the FXseries only gives a brief introduction to the communication module, specific application again in detail in later chapters.

Siemens S7-200 PLC programming examples – Belt conveyor control

To look many PLC Ladder Diagram is better for learn plc programming. you can learn the plc programming Thoughts and ideas. here is siemens s7200 plc rpgramming examples.
(1) control requirements
Motors M1, M2, M3 three drive belt conveyor.Press the start button SB1, start the order of M1, M2, M3, the interval of 3s.Press the stop button SB2, the order of the parking for M3, M2, M1, the interval of time is 3s. Three motors M1, M2, M3 respectively through the contactor KM1, KM2, KM3 connected three-phase AC power supply, with PLC control of the coil of the contactor.

(2)Address allocation table for programming elements
 Programming element
I/O terminals
(program address)
Circuit devices
(PT timer value)
 input relay
start button
Stop button
 output relay
M1 Contactor
M2 Contactor
M3 Contactor
Start first period of time
Start second period of time
Parking first period of time
Parking second period of time
Auxiliary relay
Parking holding first
period of time
Parking holding second period

(3)Ladder Diagram

PLC ladder programming

Siemens S7-300 Ladder Diagram PLC Programming Example-Control Belt

This PLC programming example is plc control belt

(1) Control requirements

Electric start belt,At the beginning of the belt has two push button switches: S1 for START and S2 for STOP;At the end of the belt also has two buttons switches: the S3 for START and STOP for the S4. You can start or stop the belt from either end. In addition, when an object on the belt reaches the end, the sensor S5 make  belt stop.

(2)Programming element symbolic address

Symbol Address
Absolute address
class type
Start button
Stop start button
Tail start button
Tail stop button

(3)Ladder diagram

PLC programming ladder diagram

Siemens PLC S7-300 Ladder Diagram Programming Example-pulse generator

Siemens plc S7-300 programming the timer can also be   a pulse generator.

(1) Control Requirements

The PLC program using a timer constitute a pulse generator,With two timers generate a pulse signal frequency of the duty cycle can be set

Timing diagram of the pulse generator

(2) Ladder Diagram

PLC Ladder Diagram

When the input I0.0 is 1, the output Q0.0 is 0 or 1 alternately, a periodic pulse signal for 3s, the pulse width is 1s.

Siemens PLC S7-300 controls the motor to start up Ladder Diagram programming examples

Today we’ll make a plc ladder diagram for siemens plc s7-300 control the motor start up. plc ladder diagram  is very important to learn plc programming.
(1) Control requirements.
There are three motors M1, M2, M3, press the start button to start M1, M2 starts after delay 5s, M3 starts again after 16s.
(2) Programming element symbol address

Programming element symbol address

(3) PLC Ladder Diagram

PLC Ladder Diagram

Siemens S7-300 plc counter becomes timer programming examples

Siemens PLC programming, how to use clock memory, extended to  timer, which is plc programming examples, explains how to write ladder diagram
In the programming use CPU memory clock,Setting MB100 clock memory, the M100.0 change cycle is 0.1s.Enter the symbol for the address I0.1, I0.1 positive edge down counter C0 to set the number, if I0.0 is 1, C0 minus 1 per 0.1s. Output symbol address Q0.0.

ladder diagram

If the I0.1 is the number of positive hops down the counter C0, if I0.0 is 1, then C0 per 0.1s minus 1. When the C0 is reduced to 0, the output Q0.0 is 1. I0.1 and a positive jump along the C0 set number and make the output to 0. Thus, after the I0.0 is 1, 2S (20 x 0.1s=2s), Q0.0 is 1, and the positive I0.1 of is reset to the Q0.0.

Siemens S7-300 plc dial switch setting Heating time programming examples

here is plc program examples about siemens s7-300 plc , You can learn about Timer instruction。

(1)Control requirements.

the operator can set the heating time with a dial switch, and the operator set the value to be displayed in a second unit in a BCD format.

(2) Defining the programming element symbol address

  System components
Start button
Single digit dial switch
Tens digit dial switch
Hundreds digit dial switch
Start heating

(3) Ladder diagram

plc ladder diagram


Siemens S7-300 plc using functional blocks To realize the clock pulse generator programming examples

Now  we learn plc programming examples for  siemens s7-300 plc,here some ladder diagram program.

(1) Control requirements.

using a timer freedom to set the clock pulse generator function (pulse duty factor 1: 1)

(2) FC1 variable

FC1 variable

(3) FC1 ladder diagram program

FC1 ladder diagram program

(4) OB1 calls ladder diagram program

OB1 call Ladder diagram program


FX2N PLC programming Initial state

learn plc programming we can use  Status at the start position of the state transition diagram ,That is the initial state, the S0~ S9 can be used as the initial condition

Initial state is originally from the STOP PLC to RUN switching instantaneous action of the special auxiliary relay M8002 driver, so that the S0 set “1””.
In addition to the initial state of the state components must be in other states after the addition of STL instructions to drive, can not be separated from the state and other ways to drive.
Programming must be the initial state in the state before the other

PLC control Three phase asynchronous motor Positive inversion

this is three phase asynchronous motor positive and reverse relay contactor control operation circuit

KM1 for the motor to run the AC contactor,KM2 for the motor reverse running AC contactor,SB2 is the positive turn button,SB3 to reverse the start button,SB1 for stop button,FR for thermal protection relay.

When the SB2 is pressed,KM1 coils pull,KM1 main contact closure,The motor begins to run forward,At the same time the KM1 auxiliary normally open contacts and the KM1 coil power pull,The positive continuous operation of the motor is realized,Press the stop button until SB1;On the contrary, when the SB3 is pressed,KM2 coils pull,KM2 main contact closure,The motor begins to run in reverse,At the same time the KM2 auxiliary normally open contacts and the KM2 coil attracting, the motor reverse continuous operation,Press the stop button until SB1;KM1, KM2 coil interlock to ensure that the power is not at the same time,The research of this task uses PLC to realize the positive and reverse PLC control of the three-phase asynchronous motor.

The external hardware output circuit using KM2, KM1 normally closed contacts to the mutual lock.

Program 1,

Start – protection – stop   instructions

X002 series in forward running the branch normally closed contacts and Y001 normally closed contact, run in reverse branch X001 normally closed and Y000 series of normally closed contacts to realize the buttons and the contactor interlocking

Program 2,

Set / reset instructions

Program 3,

Stack operation  instructions


input program.

static debug     When pressed forward the start button SB2, YO bright press the stop button SB1, Y0 off;
     When you press the start button reverse SB3, Y1 bright, press the stop button SB1, Y1 off;
When you press the start button SB2 forward when, Y0 on, press the start button SB3 when reversing, Y0 off, while Y1 bright, press the stop button SB1, Y1 off

Dynamic debugging.    When you press the forward button KM1, the SB2 is closed,
Press the reverse button to start SB3, KM1 off, while KM2 closed; press the stop button SB1, KM2 off

What is a ladder diagram? Ladder diagram programming

Ladder diagram is the most used graphic programming language, it is called the first programming language of  PLC. Ladder diagram and electrical control system circuit diagram is very similar, with intuitive and easy to understand the advantages, it is easy to be mastered by the factory electrical personnel, especially suitable for switching logic control. Ladder diagram is often referred to as the circuit or program, the design of ladder diagram is called programming.
Ladder diagram programming, use the following four basic names:

1 ,Soft Relay

Some of PLC ladder diagram programming element follows the name of the relay, such as input relay,output relay, internal auxiliary relay, etc., they are not real physical relays, that are  some storage unit (soft relay), a storage unit for each soft relay and PLC memory image register. The storage unit if the “1” state, the ladder diagram of the corresponding soft relay coil energized, the normally open contact is turned on, normally closed contact is disconnected, this is the soft relay “1” or “on” state. If the memory cell is “0”, the state of the coil and contact of the corresponding soft relay is in contrast to the above, this is  soft relay is “0” or “OFF”. The use of these “soft relay” is often called to as the programming element.

2,Flow Power”

Figure, contacts 1 and 2 is switched on, there is a supposed concept of current or Power Flow), flowing from left to right, the direction and execution when a user program is consistent with the order of the logical operations.

Power flow can only flow from left to right. Using the concept of energy flow, can help us to better understand and analyze the ladder diagram.

Figure, maybe two  directions of power flow through the contacts 5 (through contact points 1, 5, 4 or contact points 3, 5, 2), which do not meet the principles of energy current can only flow from left to right

A) the wrong ladder diagram b) the correct ladder diagram

3,Bus bar

Ladder on both sides of the vertical line is called public (Bus bar) ,. In the analysis of ladder logic, in order to borrow the relay circuit analysis method, there are conceivable between the left and right side bus (left bus bar and right bus bar) a left and right positive negative DC supply voltage, the “power flow between bus bar from left to right. You can not draw right bus bar.

4,The ladder logic solution

According to the state and the logic relation of each contact in the ladder diagram, the state of the programming elements corresponding to each coil in the diagram is obtained,is called  logical solution of ladder diagram.

Ladder logic solutions were considered by from left to right, top to bottom sequence. The results of the resolver, can be immediately utilized by the logic solver behind. – Logic be based on the input image register values, rather than resolver the instantaneous state of the external input contacts carried out.