With the progress of the times, programmable controllers gradually enter people's vision. In addition, programmable controllers bring a lot of convenience to our lives. In this article, I will explain the basic application of programmable controllers.
Initially, programmable controllers are mainly used for switching logic control. With the progress of programmable controller technology, its application areas continue to expand.
Today, programmable controllers are not only used for switching control, but also for analog and digital control, data acquisition and storage, but also monitoring the control system; can also be networked, communication, to achieve a wide range of cross-regional control and management. Programmable controllers have increasingly become an important role in the family of industrial control devices.
First, for switching control
Programmable controllers to control the switching capacity is very strong. The control of the number of points in and out, less than a dozen points, dozens of points, more than a few hundred, thousands, or even tens of thousands of points. Because it can be networked, the number of points is almost unlimited, no matter how many points can be controlled.
The logic of the control of the problem can be a variety of: combinatorial, timing; immediate, delayed; do not need to count, need to count; fixed order, random work; and so on, can be carried out.
Programmable controller hardware structure is variable, the software program is programmable, for control, very flexible. When necessary, can write more than one set, or more than one set of programs, according to the need to call. It is very adaptable to the industrial field of multi-working conditions, multi-state transformation needs.
Programmable controller for switching control examples are many, metallurgy, machinery, light industry, chemical industry, textiles, etc., almost all industrial sectors need to use it. At present, the programmable controller is the first goal, but also other controllers can not be compared with it, is that it can be easily and reliably used for switching control.
Second, for analog control
Analog, such as current, voltage, temperature, pressure, etc., its size is continuously changing. Industrial production, especially continuous production processes, often to control these physical quantities.
As an industrial control electronics, programmable controllers can not control these quantities, it is a major deficiency. To this end, the programmable controller manufacturers are in this area to carry out a lot of development. At present, not only large, medium-sized machine can be analog control, is a small machine, can also be such control.
Programmable controller for analog control, to be configured with analog and digital conversion A/D, D / A unit. These are also I/O units, but they are special I/O units.
The A/D unit converts analog data from the external circuit into digital data and sends it to the programmable controller, while the D/A unit converts digital data from the programmable controller into analog data and sends it to the external circuit.
As a special I/O unit, it still has I/O circuit anti-interference, internal and external circuit isolation, and exchanges information with input/output relays (or internal relays, which is also an area of the working memory of the programmable controller. It is also an area of the programmable controller's working memory. It can be read and written) to exchange information and so on.
The A in A/D here is mostly current, or voltage, or temperature, and the A in D/A is mostly voltage, or current. Voltage and current ranges are 0 to 5V, 0 to 10V, 4 to 20mA, and some can handle positive and negative values.
Here D, small machines are mostly 8-bit binary number, medium and large mostly 12-bit binary number.
A/D, D / A has a single circuit, there are also multi-channel. Multi-way accounted for the input and output relays more.
With A/D, D / A unit, the rest of the processing are digital, which has information processing capabilities of programmable controllers is not difficult. Medium and large programmable controllers have more processing power, not only for digital addition, subtraction, multiplication, division, but also square, interpolation, but also floating-point operations. Some also have PID instructions, the deviation system can be proportional, differential and integral operations, and then produce the corresponding output. The computer can calculate almost all of it can calculate.
In this way, the programmable controller to achieve analog control is completely possible. The unit value of control can be as small as 212 parts of the measurement range value, most of which is also sufficient.
Programmable controllers for analog control, combined A/D and D/A units, and PID or fuzzy control algorithms can be used to achieve control with high control quality.
The advantage of analog control with programmable controllers is that switching quantities can be controlled at the same time as analog control. This advantage is not available in other controllers, or the realization of control is not as convenient as programmable controllers.
Of course, if the system is purely analog, the programmable controller may not be as good as a regulator in terms of performance to price ratio. This should also be seen.
Third, for motion control
The actual physical quantities, in addition to switching, analog, and motion control. Such as the displacement of machine tool components, often expressed in digital quantities.
Motion control, the effective way is NC, that is, digital control technology. This is a computer-based control technology that was born in the United States in the 1950s. Today it is very popular and perfect. At present, the advanced countries of the metal cutting machine tools, the ratio of numerical control has more than 40% ~ 80%, some even higher.
Programmable controller is also based on computer technology, and increasingly perfect. Therefore, it can also be used for digital control.
Programmable controllers can receive counting pulses with a frequency of several k to tens of kHz. The pulse can be received in a variety of ways, and can also be received in multiple ways. Some programmable controllers also have a pulse output function, the pulse frequency can be up to tens of k. With these two functions, coupled with programmable controllers have the data processing and arithmetic capabilities, if equipped with the appropriate sensors (such as rotary encoders) or pulse servo devices (such as ring distributors, amplifiers, stepper motors), can be completely in accordance with the principle of NC to achieve a variety of control.
High- and mid-range programmable controllers, but also the development of NC units, or motion units, can be realized point control. Motion unit can also realize the curve interpolation, can control the curve movement. Therefore, if the programmable controller is configured with such a unit, it is possible to use the NC method, digital control.
Newly developed motion unit, and even issued the NC technology programming language for better digital control with programmable controllers to provide a convenient.
Fourth, for data acquisition
With the development of programmable controller technology, its data storage area is getting bigger and bigger. Such as the programmable controller of the Devison company, its data storage area (DM area) can reach 9999 words. Such a large data storage area can store a large amount of data.
Data acquisition can be done with a counter, which accumulates the number of pulses collected and transfers them to the DM area at regular intervals.
Data acquisition can also be performed with an A/D unit, which converts analog quantities to digital quantities and then transfers them to the DM area at regular intervals.
The programmable controller can also be configured with a small printer to print out the data in the DM area on a regular basis.
Programmable controller can also communicate with the computer, the computer to read out the data in the DM area, and the computer then process the data. At this point, programmable controllers become the data terminal of the computer.
Power users have used programmable controllers for real-time recording of user power consumption, in order to realize different power hours, different pricing methods, to encourage users to use more power in the low point of power consumption, to achieve the purpose of rational use of electricity and power saving.
Fifth, for signal monitoring
Programmable controller self-test signals are many, many internal devices, most users do not give full play to its role.
In fact, it can be fully utilized for programmable controllers to monitor their own work, or to monitor the control object.
Here introduces a programmable controller timer as a watchdog, the control object to monitor the work of the idea.
Such as programmable controller control of a moving part of the action to see after the application of control action is not carried out, available watchdog approach to achieve monitoring. Specific practice is to apply control at the same time, so that the watchdog timer. If the action is completed within the specified time, that is, the timer has not exceeded the warning value, has received a signal of completion of the action, then the control object is working properly, no need to alarm.
If the timeout is exceeded, it means that it is not normal and can be handled accordingly.
If the control object of the important control links, are some of these watchdog "watch", that the system will be in the palm of your hand, there is a problem, what is stuck in the link is also very good to find.
There are other monitoring work can be done. For a complex control system, especially automatic control systems, monitoring and further self-diagnosis is very necessary. It can reduce system failures, faults or find, can improve the cumulative average trouble-free operation time, reduce the fault repair time, improve system reliability.
Six, for networking, communication
Programmable controller networking, communication capabilities are very strong, there are constantly new networking structure introduced.
Programmable controllers can be connected to a personal computer for communication, the computer can be used to participate in the programming and control of programmable controllers for management, so that programmable controllers with more convenient.
In order to fully utilize the role of the computer, a computer can be implemented to control and manage multiple programmable controllers, up to 32. Can also be a programmable controller and two or more computers to communicate, exchange information to achieve multi-location monitoring of the programmable controller control system.
Programmable controllers can also communicate with programmable controllers. One-to-one programmable controller communication. Several programmable controllers can communicate. Can be as many as dozens or hundreds.
Programmable controllers and intelligent instrumentation, intelligent actuators (such as inverters), can also be networked communication, exchange of data, mutual operation.
Can be linked into a remote control system, the system range can be as large as 10 kilometers or larger.
Can form a local network, not only programmable controllers, but also high-grade computers, a variety of intelligent devices can also enter the network. Available bus network, also available ring network. The network can also set the network. Network and network can also be bridged. Networking can be thousands of programmable controllers, computers, intelligent devices organized in a network.
Nodes between the network can directly or indirectly communicate, exchange information.
Networking, communication, is adapted to today's computer integrated manufacturing system (CIMS) and intelligent factory development needs. It can make industrial control from the point (Point), to the line ((Line) and then to the surface (Aero), so that the equipment level control, production line control, factory management control into a whole, and thus can create higher benefits. This infinitely bright future has been more and more clearly shown in front of our generation.
The above applications are focused on qualitatively. Quantitatively speaking, programmable controllers are large and small. Therefore, its control range can also be large, can be small. Small only control a device, or even a component, a site; large control of multiple devices, a production line, to the entire plant. It can be said that the size of the industrial control occasions, are inseparable from the programmable controller.
Generally speaking, the industrial production process can be divided into two types; continuous production process (such as the chemical industry) and non-continuous, that is, discrete production process (such as machinery manufacturing). The former production object is continuous, can not be divided into pieces; the latter for the discrete, one piece at a time. As programmable controllers have the above aspects of the application, but also, the control of the scale can be large, can be small, so the two types of production processes have their place.
In fact, programmable controllers have been widely used in various fields of industrial production. From the industry, metallurgy, machinery, chemical industry, light industry, food, building materials, etc., almost no use to it. Not only industrial production with it, some non-industrial processes, such as building automation, elevator control also use it. Agricultural environmental parameters of the greenhouse regulation, irrigation also use it.
Programmable controllers can have a wide range of applications of the above several scopes, programmable controllers are programmable controllers of their own characteristics of the decision, but also programmable controllers are the result of the continuous improvement of technology.