1 lead it PLC
is nearly 40 years development of modern industrial control technology, because it's the computer programming is flexible, and the advantages of complete functions, wide application and control of relay system is simple, easy to use, strong anti-interference ability, combine the advantages of cheap, and itself has small volume, low power consumption, stable performance, etc, thus has been widely applied in industrial production process control, known as the three pillars of modern industrial automation (
PLC, numerical control technology, industrial robots)
One of the.
for input and output points less system can need not interface extension;
When points is large, the need for input and output expansion.
PLC products from different companies, number and extension module to the system total points is limited, when extended still cannot satisfy the need have to use the network structure, both to increase the complexity of the system, and also raise the cost of the system.
aiming at the problem of a large number of switch signal input, with Japan's mitsubishi fx series PLC as an example, this paper designed a PLC switch quantity acquisition method based on the set of scan input, with the aid of input interface board, can implement multiple switch input signal into single input points of PLC, using this method, the input points more control system, can save PLC input points, improve the efficiency of PLC information collection efficiency, to reduce the cost of control system is of great significance.
2 hardware design used for industrial field often switch, button switch signal, and according to figure 1 wiring methods usually connected to the PLC input point, this method takes the com port for all public side of switch input signal, each switch or button to access a PLC input point.
Figure 1 common switch signals and access methods to solve the problem of a large number of switch signal input, the use of signal scanning principle, we design a switch quantity based on scanning the input set of PLC input sampling method, hardware structure is shown in figure 2.
Diagram 16 switch input signal, for example, the 16 switch input signal is divided into 4 groups, and four block access interface board (
Each interface board can access four-way signal, through the diode output)
Through interface board, k1, k5, k9, k13 x1 input are connected to the PLC, and so on, k2, k6, k10/19 dated, k14 x2 input are connected to the PLC, k3, k7, k11, k15 x3 input are connected to the PLC, k4, k8, k12, k16 x4 input are connected to the PLC, 16 switch input signal and only occupies four input terminal of PLC.
4 piece of interface board respectively by PLC output 4 y1 ~ y4 gate (
A line drawing)
, such as effective y1 and y2 - y4 are invalid, gate, and the interface board I was chosen as k1 ~ k4 signal was sent into the x1 x4, when effective and y1 y2, y3, y4 is invalid, k5 ~ k8 signal was sent into the x1 x4, the signal is sent to the same way in the other two groups.
In this structure, the output y replace com as public side.
this scanning each cycle 4 times, can be divided into four times to send 16 signal to the input end of the PLC, after each scan of x1 ~ x4 in program state transfer to another location.
16 input signals only occupies four inputs and four outputs, save half of the input and output points of PLC, in be used actually can also according to the need for flexible extension, obtain higher efficiency.
If each interface board up eight switch input signal, and 4 boards, a total of 32 input signal access, take up the PLC controller
of eight input, output is still four.
when the design must pay attention to the interface board in the choice of diode, must choose high quality, stability, good diode, if there is a diode damage or breakdown situation, there will be the input signal cannot be correctly into the PLC input or input disturbance.
In addition to the group number of unfavorable and overmuch input signal, in figure 2 is the four groups, if each scanning time interval is 100 ms, is one of the four scan scan cycle that is 400 ms, the input signal of 400 ms delay possible, if too many (
Such as more than 10 groups)
Signal delay occurs, resulting in a decline in the sensitivity of the system.
figure 2 based on the group of PLC scan switch input and acquisition hardware structure FIG. 3 flow chart of software
3 software design in software design to consider two main problems.
One is, a single scan gating signal timing output to gate to the corresponding interface board, the second is to timely will scan incoming data is transferred to another location.
In this kind of design method of PLC input, in each scan cycle, each group of on-off signals of a sequence into a PLC input, so it must be before the next scan data will be the last scan in the state of switch signals and transferred to the other place is saved.
figure 3 for the software flow diagram, software program designed based on these considerations,
As shown in figure 4.
Each scan interval 100 ms, 16 after switch information collected and PLC respectively into m100 approximately ~ m115 preservation, the meaning of the directive rol and ref refresh cycle shift to the left and output respectively.
figure 4 support multipoint scanning input software implementation of PLC input 4 conclusion this paper designed a PLC switch quantity acquisition method based on the set of scan input, using the signal scanning principle, can effectively solve the existing in the industrial field of a large number of switch signal input problem, this method can greatly reduce the input points of PLC, reduce the cost for control system design, system structure stability, scalability, flexibility is good, has a certain use value and popularization meaning.
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