1. According to the wiring diagram, this is the highest guideline is not too much. First of all, before wiring must first carefully read the drawings, fully understand the intention of the designer, rather than according to the individual so-called rich experience wiring, if you find the unknown or contradictory should be the first time to contact the designer to confirm, until there is no error, wiring construction.
2. The wiring sequence should be clear, simple process with checkability. This one in practice can do very little, basically is a line to connect, box a cover to finish.
3. Learn more wiring skills, good flexibility in the use of professional tools. For example:
Q: We do PLC cabinets, terminal boards and terminals a lot of poorly handled will be loose, burrs and other phenomena, is directly stripped wire skin pressed in, or the use of pins, or sticky tin.
A: Single-core wires are directly pressed in after stripping, and multi-core wires are pressed in with cold-pressed terminals, and tin-lining is not recommended;
Q: When there are more PLC expansion modules, how is the wiring of the common and power supply terminals handled, is it directly connected in parallel to the next module through the terminals on each PLC module, or is it connected to the terminals and shorted on the terminal block?
A: We maintain the equipment in the field, we hope that the power supply in the terminals after the distribution of the short into the user points (with a line number tube or in the terminal marking to indicate where to go), so that intuitively clear, with a small impact on each other, do not want to be merged from one point to another, do not want to connect more than two wires under a terminal. For the power supply terminal row, like to use the terminal with insurance or the terminal can be disconnected between the top and bottom of the kind of short-circuit fault is very convenient to find.
01
PLC internal and external circuits
1. External circuit wiring
Figure 1 is the electrical control circuit of the contactor for motor full-voltage starting control, and the control logic is realized by AC contactor KM coil, indicator lamps HL1 and HL2, normally closed contacts FR of thermal relay, stop button SB2, start button SB1 and normally open auxiliary contacts KM of the contactor connected by wires.
After closing the QS and pressing the start button SB1, the coil KM is energized and self-locking, turning on the auxiliary contact KM of the branch where the indicator HL1 is located and the main contact in the main circuit, HL1 lights up and the motor M starts; pressing the stop button SB2, the coil KM is de-energized, the indicator HL1 goes out, and M stops rotating.
▲Figure 1 Electrical control circuit for motor full-voltage starting
Figure 2 is the external wiring diagram of a SIEMENS S7 series PLC to realize full-voltage motor starting control. The main circuit remains unchanged, the thermal relay normally closed contact FR, stop button SB2, start button SB1 and so on are connected to the input interface of the PLC as input devices, while the AC contactor KM coil, indicator light HL1, HL2 and so on are connected to the output interface of the PLC as output devices of the PLC. The control logic is realized by executing the user program written in accordance with the motor full-voltage control requirements and stored in the program memory.
▲Figure 2 PLC control wiring diagram for motor full voltage starting
2. Establishment of internal I / O image area
In the PLC memory to open up the I / O image storage area, used to store the state of the I / O signals, respectively, known as the input image register and output image register, in addition to the PLC other programmable components also have a corresponding image memory, known as the component image registers.
I / O image of the size of the area by the PLC system program to determine, for each input point of the system there is always an input image of a certain area with a corresponding, for each output point of the system also has an output image of a certain area with a corresponding, and the system's input and output point of the addressing number and I / O image of the area of the image of the register address also corresponds to the number.
When the PLC works, the state of the collected input signal is stored in the corresponding bit of the input image area, and the result of the operation is stored in the corresponding bit of the output image area. The data required by the PLC to describe the equivalent contact of the input relay or the equivalent contact of the output relay, or the equivalent coil state is taken from the I/O image area when the PLC executes the user program, and it does not have a direct relationship with the external device.
The establishment of the I/O image area makes the PLC work only with the memory of the state data stored in the address unit, and the system output is only a memory address unit to set a state data. This not only speeds up the program execution speed, but also makes the control system and the outside world to isolate, improve the system's anti-interference ability.
3. Internal equivalent circuit
Figure 3 is the PLC's internal equivalent circuit, in which the start button SB1, for example, its access interface I0.0 and the input image area of a flip-flop I0.0 is connected, when the SB1 is connected, the flip-flop I0.0 is triggered for the "1" state, and this "1" state can be used by the user program. "state can be directly quoted by the user program for the state of I0.0 contact, at this time I0.0 contact and SB1 on and off state is the same, then SB1 on, I0.0 contact state is "1", and vice versa, SB1 off, I0.0 contact state for " 0";
Because the I0.0 trigger function and relay coil the same and do not need to hardwire, so the I0.0 trigger is equivalent to a PLC internal I0.0 soft relay coil, direct reference to the I0.0 coil state of the I0.0 contact is equivalent to a normally open contact controlled by the I0.0 coil (or known as the dynamic closing contact).
▲Figure 3 Equivalent circuit inside PLC
Similarly, the stop button SB2 is connected to a soft relay coil I0.1 inside the PLC, SB2 is closed, the state of the I0.1 coil is "1", and vice versa, and the state of the relay coil I0.1 is reversed by the user program and then referenced to the state of the I0.1 contact. The state of relay coil I0.1 is inverted by the user program and quoted as the state of I0.1 contact, so I0.1 is equivalent to a normally closed contact (or dynamic break contact) controlled by I0.1 coil. The output contacts Q0.0 and Q0.1 are the physical normally open contacts of the relays inside the PLC, and once they are closed, the corresponding external KM coils and the indicator HL1 will be turned on.The PLC outputs have a common interface COM for the output power supply.
02
PLC control system
With PLC to realize the motor full-voltage starting electrical control system, the main circuit remains basically unchanged, while using PLC to replace the electrical control line.
1.PLC control system composition
Input Circuit
The function of the input circuit is to send input control signals to the PLC, and the input devices are push buttons SB1, SB2 and FR normally closed contacts. The external input control signals are fed into the corresponding input relay via the PLC, which can provide any number of normally open and normally closed contacts for programming the PLC content control circuit.
Output Circuit
The role of the output circuit is to convert the PLC output control signals into signals that can drive the KM coil and the HL1 indicator.There are a number of output relays in the PLC internal control circuit, and each output relay, in addition to the PLC internal control circuit to provide normally open and normally closed contacts for programming, also provides a normally open contact for the output circuit to connect with the output port, which is called an internal hard contact, is an internal physical normally open contact. An internal physical normally open contact. This contact drives external loads such as the KM coil and the HL1 indicator, and the KM coil in turn controls the start and stop of the motor M through the KM main contact in the main circuit. The power supply for driving the loads is provided by the external power supply, and there is a COM common terminal for the output power supply in the output port of the PLC.
Internal control circuit
The internal control circuit is formed by the user program written in accordance with the actual control requirements of the motor under control, and its function is to calculate, process and judge the status of the input and output signals in accordance with the logical relationships specified in the user program, and then obtain the corresponding output control signals to drive the output devices, such as the motor M and the indicator HL1, by means of the control signals.
The user program is written to the user program memory of the PLC by means of personal computer communication or programmer input. Modification of the user program only requires changing certain statements in the memory through the programmer and other equipment, without changing the internal wiring of the controller, thus realizing the flexibility of control.
2.PLC control ladder diagram
Ladder diagram is a kind of PLC internal equivalent into the coil of many internal relays, normally open contacts, normally closed contacts or function program block equivalent control line. Figure 5 is the PLC ladder diagram commonly used equivalent control element symbols.
▲Figure 5 Commonly used equivalent control element symbols for ladder diagrams
a) Coil b) Normally open contact c) Normally closed contact
Figure 6 is the motor full-voltage starting PLC control ladder diagram, by the FR normally closed contacts, SB2 normally closed button, KM normally open auxiliary contacts and SB1 normally open button in parallel with the unit, the KM coil and other parts corresponding to the equivalent control element symbols in series. Motor full-voltage starting control ladder in the form of similar to the contactor electrical control wiring diagram, but also with the electrical control wiring diagram there are many differences.
▲Figure 6 Motor full voltage starting control ladder diagram
The physical structure of the electrical components following the ladder diagram is different from that of the electrical components.
The coils and contacts in a PLC ladder diagram are only functionally equivalent to the coils and contacts of an electrical component. The coils and contacts in the ladder diagram are only a storage bit in the input and output memory in a physical sense, which is different from the physical structure of the electrical components.
The on/off state of the relay element in ladder diagram is different from that of the electrical element.
Ladder diagram following the electrical components of the on-off state and the corresponding memory bit of the data stored on the relevant, if the data of the memory bit is "1", the component is in the "on" state, if the bit of data for the "0 If the data in this bit is "1", the component is in the "on" state, and if the data in this bit is "0", it is in the "off" state. Different from the actual on-off state of the electrical components.
The state switching process of the relay electrical components in the ladder diagram is different from that of the electrical components.
Ladder diagram relay electrical components state switching just PLC to store the bit of state data operation, if the PLC on the normally open contacts equivalent to the storage bit data assigned to "1", the completion of the process of moving close operation, the same as on the normally closed contacts equivalent to the storage bit data assigned to "0 Similarly, if the equivalent memory bit data of a normally closed contact is assigned to "0", the dynamic break operation process can be completed, and there is no time delay in the switching operation process. The electrical components coil, contacts for dynamic closure or dynamic break switching, there must be a time delay, and generally have to go through the first after the closure of the disconnection process.
The number of contacts belonging to the relay in the ladder diagram is different from that of the electrical components.
If the PLC from the input relay I0.0 corresponding memory bit out of the bit data "0", will be deposited into another memory in a memory bit, was deposited into the memory bit becomes controlled by the I0.0 relay a normally open contact, was deposited into the data for "0 "; if the inverse operation is carried out after the bit data "0" is taken out and then deposited into a memory bit, the data deposited in the bit is "1", and the bit becomes a normally open contact controlled by the relay I0.0, and the data deposited is "0". normally closed contact.
As long as the internal memory of the PLC is sufficiently large, this bit data transfer operation can be carried out indefinitely, and each operation can produce a relay contact in the ladder diagram, which shows that the relay contacts in the ladder diagram in principle can be used indefinitely and repeatedly.
However, the coils inside the PLC can usually be referenced only once, and caution should be exercised if coils with the same address number are to be reused. Unlike PLCs, electrical components have a limited number of contacts.
The rule for drawing each line of the ladder diagram is to start from the left bus, pass through the contacts and coils (or function boxes), and terminate at the right bus. Generally, parallel units are drawn on the left side of each line, output coils are drawn on the right side, and the rest of the series components are drawn in the center.