1、For switching quantity control
  The ability of PLC to control the switching quantity is very strong. The number of points controlled in and out, less than a dozen points, dozens of points, more can be hundreds, thousands, or even tens of thousands of points, because it can network, the number of points is almost unlimited, no matter how many points can be controlled, the logic of the control can be a variety of issues: combination, timing, instant, delay, no counting, the need to count, fixed order, random work, etc., can be carried out.
  The hardware structure of the PLC is variable and the software program is programmable, which is very flexible when used for control. Multiple sets or groups of programs can be written when necessary and called as needed. It is very adaptable to the industrial site multiple conditions, multiple state transbbbbation needs.
  PLC for switching control is a lot of examples, bbbbllurgy, machinery, light industry, chemical industry, textile, etc., almost all industrial industries need to use it. At present, the goal of the first PLC, but also other controllers can not be compared with it, is that it can be easily and reliably used for switching control. 2, for analog control
  Analog quantities, such as current, voltage, temperature, pressure, etc., its size is continuously changing. Industrial production, especially the continuous production process, often to control these physical quantities.
  As an industrial control electronics, PLC can not control these quantities, it is a major deficiency, for which the PLC manufacturers are in this area for 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. PLC for analog control, to be configured with analog and digital conversion of the A/D, D / A unit. It is also the I/O unit, but it is a special I/O unit.
  A/D unit is the analog quantity of the external circuit, converted into digital quantity, and then sent to the PLC; D/A unit, is the digital quantity of the PLC into analog quantity, and then sent to the external circuit. As a special I/O unit, it still has the characteristics of I/O circuit anti-interference, internal and external circuit isolation, and bbbbb and output relays (or internal relays, which is also a zone of PLC working memory, can read and write) to exchange inbbbbation and so on.
  Here the A in the A/D, mostly current, or voltage, but also temperature. the A in the D / A, mostly voltage, or current. Voltage, current change range is mostly 0 ~ 5V, 0 ~ 10V, 4 ~ 20mA, some can also handle positive and negative values. Here the D, small machines are mostly 8-bit binary numbers, medium and large are mostly 12-bit binary numbers. a / d, d / a single, there are also multiple. Multiplex accounts for more bbbbb and output relays. With A/D, D / A unit, the rest of the processing are digital, which is not difficult for PLC with inbbbbation processing capabilities. Medium and large PLC processing power is stronger, not only can be digital addition, subtrbbbbbb, multiplication, division, but also open square, interpolation, but also floating point operations, some have PID instructions, can be the deviation of the system amount of proportional, differential, integral operations, and then produce the corresponding output, the computer can calculate almost all of it can calculate.
  In this way, the use of PLC to achieve analog control is entirely possible.
  PLC for analog control, and A/D, D / A combination of units together, and the use of PID or fuzzy control algorithms to achieve control, you can get a very high quality of control. The advantage of using PLC for analog control is that in the analog control at the same time, the switch can also be controlled. This advantage is that other controllers do not have, or control is not as convenient as the implementation of PLC. Of course, if the system is purely analog, the use of PLC may be in the perbbbbance to price ratio is not as good as the use of regulators.
  3, for motion control
  The actual physical quantities, in addition to switching, analog, and motion control. Such as the displacement of machine parts, often expressed in digital quantities. Motion control, an effective approach is NC, that is, digital control technology. This is a computer-based control technology born in the United States in the 1950s. Today has been very popular, and also very well. At present, advanced bbbbl cutting machine tools, the rate of NC has been more than 40% to 80%, and some even higher. PLC is also based on computer technology, and increasingly perfect. PLC can receive counting pulses, the frequency can be as high as a few k to tens of k Hz, available in a variety of ways to receive the pulse, but also multiplexed reception. Some PLC and pulse output function, pulse frequency can also reach tens of k, with these two functions, coupled with the PLC has data processing and computing capabilities, if equipped with the corresponding sensors (such as rotary encoders) or pulse servo device, it can be fully in accordance with the principle of NC to achieve a variety of control. High-grade, mid-range PLC, but also developed NC unit, or motion unit, can achieve point control. Motion units can also achieve curve interpolation, can control the curve movement.
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